Some thecate hydroids (Cnidaria: Hydrozoa) from off New Caledonia collected during KANACONO and KANADEEP expeditions of the French Tropical Deep-Sea Benthos Program

Thirty-six species of various thecate hydroids occur in two recent, deep-water collections from off New Caledonia. Of these, nine are new, namely Solenoscyphus subtilis Galea, sp. nov., Hincksella immersa Galea, sp. nov., Synthecium rectangulatum Galea, sp. nov., Diphasia alternata Galea, sp. nov., Dynamena opposita Galea, sp. nov., Hydrallmania clavaformis Galea, sp. nov., Symplectoscyphus acutustriatus Galea, sp. nov., Symplectoscyphus elongatulus Galea, sp. nov. and Zygophylax niger Galea, sp. nov. The male and female gonothecae of Caledoniana decussata Galea, 2015, the female gonothecae of Caledoniana microgona Galea, 2015, as well as the gonothecae of both sexes of Solenoscyphus striatus Galea, 2015 are described for the fi rst time. The systematic position of the genera Solenoscyphus Galea, 2015 and Caledoniana Galea, 2015 is discussed on both morphological and molecular grounds, and both are confi dently placed within the family Staurothecidae Maronna et al., 2016. In light of the molecular data, the genera Billardia Totton, 1930 and Dictyocladium Allman, 1888 are assigned to the families Syntheciidae Marktanner-Turneretscher, 1890 and Symplectoscyphidae Maronna et al., 2016, respectively. The previously undescribed gonothecae of Hincksella neocaledonica Galea, 2015, and the male gonothecae of Sertularella tronconica Galea, 2016, were found. Thyroscyphus scorpioides Vervoort, 1993, a peculiar hydroid with putative stem nematothecae, is redescribed and assigned to the new genus Tuberocaulus Galea, gen. nov. Noteworthy new records from the study area are: Tasmanaria edentula (Bale, 1924), Hincksella sibogae Billard, 1918, Dictyocladium reticulatum (Kirchenpauer, 1884), Salacia sinuosa (Bale, 1888) and Billardia hyalina Vervoort & Watson, 2003. Most species are illustrated to facilitate their identifi cation, and the morphology of the new ones is compared to that of their related congeners.


Introduction
The hydroid fauna of New Caledonia has received increasing attention over the last three decades, owing greatly to the rich materials collected in the frame of the French Tropical Deep-Sea Benthos Program (Bo uchet et al. 2008). Several resulting studies, occasionally including specimens from additional areas of the tropical western Pacifi c, have been published to date, namely Ve rvoort (1993), An sín Agis et al. (2009,2014,2016), Peñ a Cantero & Vervoort (2010) and Galea (2015aGalea ( , 2016. Two recent expeditions have also provided hydroid material: KANACONO took place between 8-31 August 2016 around the Isle of Pines, southeast of Grande Terre, while KANADEEP was conducted between 31 August-27 September 2017 in the Coral Sea. Only a part of the hydroids gathered during these expeditions is treated here, and concerns various families of Leptothecata Corn elius, 1992, among which the Staurothecidae Maro nna et al., 2016, Syntheciidae Mark tanner-Turneretscher, 1890, Sertulariidae Lamo uroux, 1812, Sertularellidae Maronna et al., 2016, Symplectoscyphidae Maronna et al., 2016and, only superfi cially, Zygophylacidae Quel ch, 1885. Although a number of species from the area has been dealt with by Vervoort (1993) and Galea (2015aGalea ( , 2016, additional records (including new species) are provided, along with supplementing data on morphology.

Material and methods
Study methods were described in Galea (2007Galea ( , 2008. Stat ion numbers, as indicated in the text, are preceded by a two-letter prefi x referring to the sampling gear used to secure the material, either a beam trawl (CP), a rocky bottom dredge (DR) or a Warrén dredge (DW). The material, fi xed and preserved in ethanol, is deposited in the collections of the Muséum national d'histoire naturelle (MNHN) of Paris, France, and catalogue numbers are indicated as MNHN-IK-2015-followed by 3-digit numbers. Fragments, cut off from a number of specimens with suffi cient coenosarc, were used to extract DNA. The residual perisarc, mounted as permanent microscopic slides, is deposited as voucher specimens in the collections of the Muséum d'histoire naturelle of Geneva (MHNG), Switzerland; catalogue numbers, in this case, are indicated as MHNG-INVE-followed by 6-digit numbers, while the DNA isolates are identifi ed by the prefi x DNA followed by 4-digit numbers.
Molecular biological methods, as well as maximum likelihood analyses with Phyml ver. 2. 4.4. (Guindon & Gascuel 2003), were performed as described in Schuchert (2014Schuchert ( , 2016. About 600 bp of the large mitochondrial ribosomal RNA (16S) was amplifi ed using the primers SHA (ACGGAATGAACTCAAATCATGT) and SHB (TCGACTGTTTACCAAAAACATA) (Cunningham & Buss 1993) (35 cycles, profi le: 20 sec at 94°C, 45 sec at 50°C, and 120 sec at 68°C). Not all extractions gave positive PCR results. All resulting 16S sequences were deposited in the GenBank database under the accession numbers MK073078 to MK073115. The deposited set comprises also some new sequences of samples originating from outside New Caledonia that proved useful in the context of the present study. Their collection data and voucher numbers can be obtained via their accession numbers given in Fig. 20, and a search in the GenBank database. Additional 16S sequences of related taxa were retrieved from GenBank. Also, their meta-data can be obtained via the accession numbers. Two species names were not used as given in GenBank, namely: Symplectoscyphus turgidus (FJFJ550462) is referred to as Xingyurella turgida (Trask, 1857) (Song et al. 2018), while Sertularella sanmatiasensis El Beshbeeshy, Class Hydrozoa Owen, 1843Subclass Hydroidolina Collins, 2000Order Leptothecata Cornelius, 1992 Family Staurothecidae Maronna et al., 2016 Caledoniana decussata Galea, 2015 Fig . 1A ; MNHN-IK-2015-362 • a colony without gonothecae, 6.0 × 3.5 cm (height × width; the same applies to all subsequent materials and species), with one side branch; same collecting data as for preceding; MNHN-IK-2015-362 • a colony, 2.3 × 3.7 cm, with 2 side branches, carrying an immature female gonotheca; same collecting data as for preceding; MNHN-IK-2015-362 • a ca 9 × 7 cm, branched (up to 2 nd order branches), fully fertile male colony; same collecting data as for preceding; a short, distal fragment was cut off for DNA extraction, DNA1345; MNHN-IK-2015-362 • originally a 4.5 cm high colony with one side branch, the latter bearing an immature, likely female, gonotheca; same collecting data as for preceding; a 1 cm long fragment from the branch was cut off for DNA extraction, DNA1346; voucher MHNG-INVE-120780; MNHN-IK-2015-362 • a ca 11 × 12 cm, fan-shaped, fully fertile male colony; off New Caledonia, stn DW4728; 22°43′ S, 167°02′ E; 150 m; 20 Aug. 2016; KANACONO leg.; a short, distal fragment was cut off for DNA extraction, DNA1347; voucher MHNG-INVE-120781; barcode identifi er MK073079; MNHN-IK-2015-365.

Remarks
The decussate arrangement of the hydrothecae, although quite irregular within a given colony, occurs in all the material examined, a condition never met within the two other species of the genus, C. alata Galea, 2015 andC. microgona Galea, 2015. The species is monoecious and sexually dimorphic. The gonothecae arise laterally from below the hydrothecal bases. The male ones are club-shaped, ca 3200 μm long and 1170 μm wide (one gonotheca measured), tapering below into an indistinct pedicel; there is no noticeable aperture distally. The female gonothecae are large, ca 3890 μm high and 2630 μm wide in lateral view (one gonotheca measured), recalling a closed hand wearing a mitten; they are bilaterally symmetrical and contain a large, globular, inner cavity protecting at least a large, ovoid oocyte, the latter ca 925 × 590 μm; the aperture is half-moon-shaped, faces downwards, and does not appear to possess an opercular apparatus.
GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia Although the morphology of the fully-formed gonotheca of C. alata, the type species of the genus, is as yet unknown, it is assumed that the specimen depicted by Galea (2015a, Fig. 2A) is likely to adopt a similar shape to that of its counterparts produced by both C. decussata and C. microgona (see below), thus further justifying their assignment to the same genus.
The three species of Caledoniana Galea, 2015 were included provisionally in the family Sertulariidae Lamouroux, 1812 (Galea 2015a), but it is now demonstrated that, at least C. decussata and C. microgona, belong instead to the Staurothecidae Maronna et al., 2016 (see 'Molecular study' section).
As noted earlier by Galea (2015a), C. decussata shows affi nities with Staurotheca megalotheca Vervoort & Watson, 2003, especially regarding the size and the decussate arrangement of their hydrothecae. However, the gonothecae of the latter differ much from those of both C. decussata and C. microgona, in having a small, rounded, eccentric, sub-terminal aperture borne on a short neck region, unless it is proved that its gonothecae are sexually dimorphic, thus strongly resembling to the males of "Solenoscyphus" striatus Galea, 2015a (see below). Anyway, it could be reasonably assumed that S. megalotheca is a true staurothecid hydroid, although its assignment to a given genus is impossible in the absence of evidence from molecular data.
In addition, Giganthotheca maxima Vervoort & Watson, 2003(Vervoort & Watson 2003: fi g. 26E-F) has female gonothecae approaching the morphology of those met with in both C. decussata and C. microgona, suggesting not only a reasonable assignment of this species to the Staurothecidae, but also a possible genus transfer to Caledoniana. But, again, only molecular data are expected to solve the intricacies of this species group.

Remarks
The hydrothecae are closer to one another in this species than in C. decussata and, as stated by Galea (2015a), their adaxial wall is comparatively shorter, these two characters readily distinguishing them. Like the previous species, C. microgona also appears sexually dimorphic and forming monoecious colonies. Its specifi c name is obviously inappropriate, as the hydroid was originally described based on specimens provided with 'small', saccular gonothecae that were not recognized then as being male. The female gonothecae are similar to those described in C. decussata (see above), but are of comparatively larger proportions (ca 6890 μm long and 3715 μm wide, when seen laterally; one gonotheca measured).

Distribution
Only known from off New Caledonia (Galea 2015a;present study).

Remarks
Colonies larger (up to 10 cm high and 8 cm wide) than those described originally by Galea (2015a) occur in the present collection, as exemplifi ed by material MNHN-IK-2015-364. The hydrorhiza is a rooted mass of stolonal fi bers fi rmly anchoring the colonies to their substrates. The colonies are fl accid, unable to support themselves when out of liquid; fl abellate, with indistinct main stems, except for a short, proximal portion (ca 1 cm long) above the origin from hydrorhiza, then irregularly branching, forming up to 5 th order branchlets. Stem and main branches are strongly fascicled. The branches are almost straight, except proximally, where they curve upwards immediately after their origin. The largest colony is fertile and carries female gonothecae; they originate laterally from below the hydrothecal bases at sites conspicuously marked by comparatively thinner perisarc than in the rest of the colony, forming rounded, fi lmy patches. The gonotheca is bilaterally symmetrical; broadly piriform, gradually tapering in its lower half into an indistinct pedicel; upper half globular, provided with a number of hollow spines arranged into two whorls (4-5 in the upper one, 8-9 in the lower one); one side of the gonotheca (that facing its corresponding hydrotheca) is provided with a pair of quadrangular crests forming two closelyset 'lips', leaving a slit-like passage for a few, large oocytes (badly preserved in present material); the spines, occasionally with truncated tips, have their bases prolonged downwards over the gonothecal wall as broad, prominent, rounded ridges, those from the lower whorl reaching almost the gonothecal base.  European Journal of Taxonomy 562: 1-70 (2019) The colonies are monoecious and there is a notable sexual dimorphism of the gonothecae. Indeed, material MNHN-IK-2015-368 bears male gonothecae. Similarly to the females, they arise laterally from below the hydrothecal bases, and are bilaterally symmetrical; broadly amphora-shaped, base appressed to its corresponding hydrotheca and tapering abruptly into indistinct pedicel, perisarc fi nely and denselystriated basally; slightly fl attened laterally, distally a short neck region bearing apically a small, rounded aperture; neck inclined to one side.
A peculiar morphotype of this species (Figs 2B, 32F-K) occurs in several samples, viz. MNHN-IK-2015-377 to MNHN-IK-2015-381. Its main distinguishing features rely in its more compact appearance of the colonies (compare Fig. 2B and 2A, respectively), the hydrothecae closer to one another (compare Fig. 3F and 3A), adnate for about half their length to their corresponding internodes.
In material MNHN-IK-2015-380, the female gonothecae are provided with a number of hollow, distally truncated, occasionally twin spines arranged into two whorls.
As stated earlier by Galea (2015a), this species does not resemble either S. candelabrum Galea, 2015 (type species of the genus) or S. decidualis Galea, 2015, especially in colony form, although all possess rounded, fi lmy, deciduous hydrothecal opercula. Unlike S. striatus, the last two species form regularlypinnate colonies, their perisarc is entirely smooth, and there is no conspicuous raised collar of thickened perisarc just below their hydrothecal aperture. In addition, the cladia of S. candelabrum are spirally twisted proximally, and its hydrothecae possess a conspicuous pattern of internal perisarcal thickenings. Gonothecae are only known in S. striatus, and the females -notably -resemble those of some species of Staurotheca, e.g., S. echinocarpa (Allman, 1888) ( Peña Cantero & Vervoort 2003, suggesting that the present species belongs to the family Staurothecidae. Similar female gonothecae were also described in Giganthotheca raukumarai Vervoort & Watson, 2003(Vervoort & Watson 2003: fi gs 27B-C, 28B), s uggesting that this species could be confi dently removed from the Sertulariidae and reasonably assigned to the Staurothecidae, as noted above for G. maxima. In addition, the gonothecae illustrated by these authors (Vervoort & Watson 2003: fi g. 29B, D) are undoubtedly male, and come morphologically close to those of S. striatus. However, the relationships between G. raukumarai and S. striatus are far from fully understood, a nd only a molecular evidence is expected to clarify the case.
As it will be shown in the 'Molecular study' section at the end of this report, S. decidualis does not cluster with either S. striatus or S. subtilis sp. nov. (for description, see below), suggesting that they are not congeneric. Given the morphological peculiarities of S. candelabrum, it could be justifi ably assumed that it forms a so-far monotypic genus, while S. decidualis, on one hand, and both S. striatus and S. subtilis sp. nov., on the other hand, could well belong to two undescribed genera. For this reason, when combining the genus Solenoscyphus to one of these three species, it is preceded by a question mark, pending additional data to clarify their taxonomic statuses. For additional comments, see the 'Molecular study' section.

Distribution
Only known from off New Caledonia (Galea 2015a;present study).

Etymology
From the Latin 'subtīlis', meaning 'slender', to describe the shape of its hydrothecae.

Description
Colonies fl abellate, up to 4.1 cm high and 2.3 cm wide, arising from root-like hydrorhiza fi rmly anchoring the colony to its substrate. Main stem indistinct, except for its basal 1-3 mm above origin from hydrorhiza, then branching irregularly and forming up to 2 nd order branchlets; lightly fascicled basally, grading to monosiphonic distally; division into internodes indistinct; stem and branches with similar structure: each equivalent of internode moderately-long, slightly geniculate, bearing a hydrotheca distally; 1 st internode of a side branch comparatively longer than subsequent ones; branches given off nearly perpendicularly to axis of higher order branches, but rapidly pointing upwards at geniculation introduced by 1 st hydrotheca. Hydrothecae alternate, in two parallel, coplanar rows; exceedingly long, cylindrical, adnate for ca ¼ their length to the corresponding internodes; free adaxial and abaxial walls parallel and straight; adnate adaxial wall curved, ending in basal perisarc plug; there is no complete base for the hydrotheca, but only a short lamellar projection of the perisarc on abaxial side; a conspicuous raised collar of thickened perisarc immediately below the rounded aperture; opercula not observed. Perisarc straw colored to lightly dark in older parts, fi nely and densely-striated throughout the colony. Gonothecae unknown.

Remarks
The present species comes close to S. striatus through the appearance of its colonies and their hydrothecae with striated walls and thickened apertures. Evidence from molecular data confi rms the fact that they are, indeed, congeneric (see 'Molecular study' section below). As a specifi c difference, S. subtilis sp. nov. has comparatively slenderer (hence its specifi c name) and less adnate hydrothecae (compare Fig. 3M and 3B).

Distribution
Only known from off New Caledonia (present study).

Remarks
The present material, forming pinnate colonies with lightly fascicled stems and long, tubular, weakly adnate hydrothecae, is in full agreement with the holotype described earlier by Galea (2015a). The perisarc of the colony (including that of the hydrothecae) is uniformly smooth, and the hydrothecal rim is thickened distally for only a very short distance (ca 40 μm) just below the aperture.
Despite forming regularly-pinnate colonies provided with tubular hydrothecae possessing rounded, deciduous opercula, the present species and S. candelabrum may prove to not be congeneric. The available 16S sequences place this species clearly outside the clades of Solenoscyphus and Staurothecidae ( Fig. 20 and 'Molecular study' section), but without any supported relationships to other taxa. This makes it likely that this species does not belong to the genus Solenoscyphus. However, the available 16S data do not resolve suffi ciently well the family relationships, and additional markers are needed for this purpose. Therefore, and also because no diagnostic traits are evident, we decided to leave it in the genus Solenoscyphus until a more detailed study allows fi rmer conclusions.

Distribution
Only known from off New Caledonia (Galea 2015a; present study).

Remarks
The present material likely represents a branch fragment, since no (remains of) apophyses could be seen as in a portion of stem. It was likely fertile, but all gonothecae are now lost; their attachment points are clearly visible in its proximal part, while future foramina could be noted distally as rounded, fl imsy perisarc patches below the hydrothecal bases. The hydrothecae are partly damaged (especially their margins) due to the collecting technique, and some are fi lled in with sand particles. Their morphology, combined to their dimensions (adnate wall = 1215-1290 μm long, diameter at aperture = 480-505 μm, maximum width = 515-540 μm) point, with little doubt, towards T. edentula, as described by Vervoort & Watson (2003).
On the other hand, "a low operculum of one saucer-shaped valve, much torn and usually collapsed inward" was noted in T. aegis Watson & Vervoort, 2001, the type species of the genus (Watson & Vervoort 2001: 172).
Its gonotheca shows morphological affi nities with those of species of Staurotheca, e.g., S. amphorophora Naumov & Stepanjants, 1962(Stepanjants 1979. In addition, the hydrothecal shape and the gonothecae provided with apical spines in T. pacifi ca Vervoort & Watson, 2003 (see original account), suggest possible affi nities with the Staurothecidae, as well. New molecular evidence is expected to shed light on the systematic position of the genus.

Distribution
Off northern New Zealand (Vervoort & Watson 2003) and off New Caledonia (present study).

Description
Colony erect, up to 4.5 cm high, arising from creeping, branching, tortuous stolon. Stem simple, monosiphonic, composed of a short (ca 1 cm long), proximal, smooth part, and a distal, comparatively longer hydrothecate and hydrocladiate part, the latter divided almost regularly into internodes by GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia means of transverse nodes; each internode slightly geniculate, composed of an indistinct apophysis supporting a cladium, an axillary hydrotheca associated to it, and two alternate hydrothecae above. Cladia generally alternate, coplanar, usually unbranched, divided into internodes by means of transverse nodes; up to 1.1 cm long and composed of up to ten hydrothecae internodes; fi rst internode with a long, athecate, proximal part and two alternate hydrothecae distally; remainder of hydrocladium composed of internodes with three successive, alternate hydrothecae. Hydrothecae with the same shape and size on both stem and cladia; borne on short apophyses, often renovated several times; exceedingly long, tapering imperceptibly from aperture to base, slightly asymmetrical, proximal adaxial wall slightly more convex than abaxial wall, elsewhere both straight; base with annular constriction to which the base of the hydranth attaches; rim circular, not everted; perisarc thin, smooth, transparent and easily collapsible; hydranths without caecum, with 20-22 long, fi liform tentacles. Gonothecae not observed.
Occasionally, the stem internodes bear three alternate hydrothecae (instead of only two) above the axillar hydrotheca; consequently, the cladia fl anking them are given off on the same side of the stem. Similarly, two cladia separated by an axillary stem hydrotheca were found. Aberrant, additional, 'twin' cladia are given off at the same level from the lower half of the stem, and point towards either the frontal or dorsal sides of the colony. Moreover, one distal cladium shows the beginning of secondary branching below one of its hydrothecae.

Description
Colonies erect, up to 4.3 cm high, arising from root-like hydrorhiza strongly anchoring the colony to its substrate. Stems simple, fascicled for most of their length, grading to monosiphonic distally; perisarc thick, brownish; division into internodes indistinct; equivalents of internodes with quite regular structure, composed of a proximal apophysis supporting a cladium and its associated axillar hydrotheca, two alternate hydrothecae above, and a second, distal cladial apophysis given off on opposite side, together with its associated axillar hydrotheca; occasionally three instead of only two alternate hydrothecae  GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia intervene between the proximal and distal cladial apophyses. Cladia alternate, coplanar, borne on short stem apophyses separated from their 1 st internodes by distinct oblique nodes; cladia distant of 2.5-3 mm on each side; division by nodes indistinct, but each equivalent of internode relatively short, widening abruptly distally to accommodate a hydrotheca; internodes collinear. Hydrothecae alternate, in two parallel, coplanar rows; cup-shaped, deeply immersed into their corresponding internodes, leaving only a short portion of their adaxial wall free; abaxial wall straight to slightly convex, adnate adaxial wall distinctly curved, forming large perisarc plug basally; there is no complete base for the hydrotheca, as the abaxial wall invaginates basally for only a limited extent at junction between the hydrothecal lumen and internode; aperture circular, rim smooth. Gonothecae inserted slightly laterally under the bases of cladial hydrothecae; saccular, fl attened 'dorso-ventrally', tapering basally into indistinct pedicel, distally rounded; no distinct aperture.

Remarks
This species, through its colony structure and origin of gonothecae, comes close to the type species of the genus, H. sibogae Billard, 1918. It is distinguished from it through its comparatively shorter internodes, and much immersed hydrothecae (compare Fig. 7A-E and 7K-L).
According to the present concept (Bouillon et al. 2006), the genus Hincksella Billard, 1 918 includes not only species forming pinnate colonies, but also congeners with simple, unbranched stems. Among the former category, H. alternans (Allman, 1888) gives rise to gonothecae from within the hydrothecal lumina, while H. formosa (Fewkes, 1881), the present new species, as well as H. sibogae produce external gonothecae. As for H. indiana Millard, 1967, a species with so-far undescribed gonot hecae, it could instead belong to Staurotheca Allman, 1888.
Owing to the above-mentioned features, it is likely that the genus Hincksella is polyphyletic. The 16S tree, indeed, shows that the four included species of Hincksella do not group into a common clade (see Fig. 20 and the 'Molecular study' section) and are rather scattered.

Distribution
Only known from off New Caledonia (present study).

Remarks
Unlike the holotype, some colonies in the present material are fertile. The gonothecae, of undetermined sex, are given off from within the hydrothecal lumina; broadly ovoid, ca 1420 μm long (and ca 1505 μm long including the spines, only one measured), laterally fl attened (ca 1080 μm wide on widest side, only one measured), with 9-12 transverse ridges on both fl attened sides, not meeting laterally, where two longitudinal, rounded, smooth 'ridges' are present. The small (ca 55 μm wide), rounded aperture is placed sub-apically, on a short, conical neck region, sometimes projecting outwards. The pair of apical 'horns' (distant of ca 1545 μm at their tips) is variably developed among colonies; in material MNHN-IK-2015-386, for example, they are almost indistinct, while an unequal development could be observed in sample MNHN-IK-2015-387.
In the light of the present fi ndings, it could be noted that the fully-formed gonothecae of H. neocaledonica are similar to those of H. cornuta Galea, 2015 through both their size and shape (compare Fig. 7J to Galea 2015a: fi g. 5D). However, these species can be readily distinguished on characters displayed by their trophosomes (compare Galea 2015a: fi gs 5E and 5A, respectively).
Unlike the type species of the genus, H. sibogae Billard, 1918 (see below), the present hydroid does not form rather tall colonies with fascicled stems, and its hydrothecae protrude for a long distance from the internodes. It comes close instead to Cyclonia gracilis Stechow, 1921 (now included in the synonymy of H. pusilla (Ritchie, 1910), see Galea (2010: 20) and Galea & Ferry (2015: 236)), suggesting a possible future resurrection of the genus Cyclonia Stechow, 1921 to accommodate a group of species with short, simple, monosiphonic stems, long, tubular hydrothecae, and gonothecae arising from within the hydrothecae (occasionally also from the stolon, as in H. pusilla).

Remarks
The present material agrees well with the descriptions given by Billard (1925) and Vervoort & Watson (2003), and it is characterized by the following: a) the unbranched hydrocaulus is fascicled for most of its length; b) its main tube is undivided and has a regular structure, with equivalents of internodes composed of a basal cladial apophysis and its associated axillary hydrotheca, two alternate hydrothecae above, and a second cladial apophysis (on side opposite to preceding one) with its associated axillary hydrotheca; c) hydrocladia are simple and undivided into internodes, up to 1.3 cm long, and bear up to 13 alternate hydrothecae; the fi rst internode is comparatively longer than subsequent ones and provided with a couple of proximal twists; ordinary internodes are moderately-long; d) the hydrothecae are immersed for about half their adaxial length into their corresponding internodes, and they narrow basally; their base is convex, entire, with occasional fenestrae below (as sites for the origin of gonothecae); e) the hydranth is attached to the lower third of the inner hydrothecal wall; f) the perisarc of the colonies is rather thin and easily collapsible, especially on hydrothecae.

Description
Colonies erect, bushy, up to 18 cm high, arising from root-like hydrorhiza composed of tortuous, branching and anastomosing fi bers fi rmly adhering to the substrate; usually, profuse colonies with strongly fascicled base, up to 1 cm wide, of varied length, although smaller colonies composed of many independent stems exist. Stems diverging at varied angles from their common base; composed of a smooth, basal athecate and ahydrocladiate part of varied length, and a much longer, distal part bearing both hydrothecae and hydrocladia; division into internodes not always distinct but, when present (nodes transverse), each internode composed of a pair of opposite hydrothecae proximally, followed by a pair of opposite apophyses supporting cladia and their associated axillary hydrothecae, as well as a second pair of opposite hydrothecae above; often, the hydrothecae are damaged, leaving scars in the stem, and not regenerating subsequently. Stem apophyses short, delimited from corresponding cladia by transverse constrictions of the perisarc, obvious mainly on upper parts of the colonies. Cladia given off laterally and slightly upwards in opposite, coplanar pairs; cladia distant of 3-4 mm, up to 1.8 cm long and bearing up to 18 thecate 'internodes'; division by nodes indistinct, occasionally a transverse constriction of the perisarc intervenes between successive pairs of hydrothecae; the fi rst 'internode' bears an unpaired hydrotheca facing downwards, while the 2-4 subsequent internodes display subalternate pairs of hydrothecae, changing gradually to strictly opposite distally. Often, the cladia show signs of breakage and subsequent regeneration at level of the proximal most internode; in this case, the fi rst internode, similarly to the subsequent ones, bears invariably a pair of strictly opposite hydrothecae. Hydrothecae deep, cylindrical, curved outwards, adnate to the corresponding internode for most of their length; free adaxial wall short, slightly concave, perisarc thin, gently fl aring distally; adnate adaxial wall distinctly curved, perisarc moderately thick, ending downwards into perisarc plug; abaxial wall more or less straight, distal ⅔ with distinctly thickened perisarc, often forming an internal swelling in middle, distal end slightly everted; aperture circular, rim relatively scooped in lateral view; up to three closely-set renovation could be note occasionally. Gonothecae, generally occurring in pairs, replace the (strongly) damaged stem hydrothecae in the lower halves of the colonies, arising from a hole in their adnate adaxial wall; urn-shaped, laterally fl attened and thus bilaterally symmetrical; in a frontal view of the colonies, the gonothecae show their narrowest side; fl attened sides are provided with 6-7 broad, convexly-arched ridges, the distalmost being the most prominent, grading proximally to the less conspicuous; viewed from their narrowest sides, the gonothecal ridges adopt a concave shape. Male and female gonothecae (sexes not always discernible), similar in shape. Female gonothecae with ca ten large, ovoid eggs.

Remarks
In rare instances, there can be no additional pair of hydrothecae between two successive pairs of cladia other than the axillar hydrothecae associated to the lower pair of cladia. In other cases, besides the axillary hydrothecae, only one pair (instead of two) of hydrothecae above separate two successive pairs of cladia. In one instance, a gonotheca replaced one cladium of a pair.
There is little doubt that the present material belongs to the species of Millard (1957), especially giving the following features: 1) the presence of a thick, tangled hydrorhiza, "with diameter of stolons equal to that of stem" (Millard 1957); as noted by Millard (1975), in "rich colonies the hydrorhizal tubes may rise up from the surface in a tangled bundle simulating a fascicled stem, the individual tubes anastomosing with one another and with the bases of the stems"; 2) the distinctive segmentation of the stem; 3) the presence of an unpaired proximal hydrotheca, followed by a few subopposite pairs; 4) the shape and size of hydrothecae, especially their narrow base, "widening strongly to margin, adnate for most of its length, only very slightly bent outwards […]. Margin smooth, everted […]. Diaphragm oblique, with outer edge GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia reaching sometimes as far as half-way up the abcauline wall. Perisarc thin, sometimes thickened below margin on abcauline wall" (Millard 1957: 204).
The gonothecae, were described subsequently by Millard (1980) and, in her material, they arose directly from the hydrorhiza or "from with the ends of short tubes which are probably damaged stems or hydrorhizal fi bers" (Millard 1980: 144). European Journal of Taxonomy 562: 1-70 (2019) A closely related congener (or, possibly, a mix of two species) to both S. hians and S. rectangulatum sp. nov. (see below) is the one likely erroneously assigned by Vervoort & Watson (2003) to S. protectum Jäderholm, 1903. Indeed , these authors mention a basally fascicled colony with stems up to 12 cm high (NZOI Stn I85), and the gonotheca described and illustrated in their fi g. 60F shows obvious similarities to those of the two species discussed herein. However, since there is no formal description provided by these authors, their material could not be assigned with certainty to one of the species dealt with herein. In addition, it should be stressed that S. protectum has comparatively smaller hydrothecae, and its gonothecae are radically different (Galea 2007: 77, fi g. 18E-J, table 31, as S. robustum Nutting, 1904).

Distribution
South Africa (Millard 1957) and New Caledonia (present study). Galea, sp. nov. urn:lsid:zoobank.org:act:6791A674-EFEB-4666-A21A-C83247D402F3 Figs 6G-H, 8G-K; Table 4 Diagnosis Profuse colonies comprising multiple, possibly auto-epizoic stems, forming a common, fascicled base. Above, stems monosiphonic, divided into long internodes, composed of a proximal pair of hydrothecae and a distal pair of cladial apophyses together with their associated axillary hydrothecae. Cladia with proximal, unpaired hydrotheca facing downwards, followed by additional pairs of hydrothecae adopting gradually a strictly opposite arrangement towards the distal end. Hydrothecae large, tubular, adnate for about half their adaxial length; free adaxial and abaxial walls straight and imperceptibly convergent GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia distally. Gonothecae of varied origins, urn-shaped, laterally fl attened, with 6-7 convex ridges on their broadest sides, these becoming concave on their narrowest sides; aperture on top of an apical dome.

Etymology
The specifi c name results from the fusion of two Latin words, 'rectus, -a, -um', meaning 'straight', and 'angŭlātus, -a, -um', meaning 'provided with angles', to illustrate the approximate shape of the hydrothecae in lateral view. Additional material PACIFIC OCEAN • two colonies, one comprising fi ve stems fused basally, up to 11 cm high, some bearing gonothecae on both cauli and hydrorhiza, and the other composed of two independent stems without gonothecae, arising from the same substrate, and attaining ca 7 cm in height; off New Caledonia, stn CP4985; 20°49′ S, 160°57′ E; 480-540 m; 10 Sep. 2017; KANADEEP leg.; MNHN-IK-2015-500.

Description
Colonies erect, up to 11 cm high, composed of either independent or basally-fused stems arising from tortuous, creeping, branching, anastomosing hydrorhizae. Stems unbranched, either monosiphonic or lightly fascicled basally; in the latter case, auxiliary tubes run up and down the stems, forming additional hydrorhizal fi bers. In profuse colonies, there seems to be a tendency to auto-epizoism, with new stems settling down on older ones, and forming bunches arising from a common, fascicled base. Basal parts of individual stems, above their common base, of varied length, monosiphonic, ahydrothecate and acladiate, with smooth perisarc; remainder of stem, comparatively longer, divided into regular internodes by means of transverse constrictions of the perisarc, more obvious in the upper parts; each internode long, composed of a pair of opposite hydrothecae proximally and a pair of opposite apophyses above, together with their associated axillary hydrothecae; pairs of hydrothecae widely-spaced; stem apophyses supporting the cladia distant of 4-4.5 mm; there is no very distinct node at junction between apophysis and cladium, although a slight notch in the perisarc of upper side could sometimes be noted. Most stem hydrothecae, especially those situated proximally, damaged and not regenerated subsequently. Cladia up to 17 mm long, given off at wide angle with the stem; pairs of opposite cladia coplanar; divided into irregular internodes by means of transverse nodes; proximal most internode with a long, smooth, athecate base, an unpaired hydrotheca facing downwards, followed by a distinctly subopposite pair of hydrothecae, and a distal pair of nearly opposite hydrothecae; occasionally, this internode is devoid of the second, and hence distalmost, pair of hydrothecae, the latter being confi ned to the next internode; subsequent internodes with either two or three strictly opposite pairs of hydrothecae; a fully-formed cladium comprises, besides the unpaired proximal hydrotheca, up to nine pairs of thecae. In most European Journal of Taxonomy 562: 1-70 (2019) colonies, many cladia, especially the basal ones, show signs of breakage and subsequent regeneration (a distinctive, transverse breakage line could be noted); in this case, the cladia comprise exclusively pairs of strictly opposite hydrothecae, the proximal most, unpaired one being replaced. Hydrothecae on both stems and cladia form two parallel, coplanar rows; almost tubular, adnate for slightly more than half their adaxial length to the corresponding internodes; free adaxial and abaxial walls slightly and gradually convergent towards distal end; aperture circular, rim slightly everted; hydranths with ca 18 fi liform tentacles. The gonothecae arise often in pairs from scars of damaged hydrothecae on proximal parts of the stems; occasionally, they can replace a cladium of a pair, arise from auxiliary tubes of the stem, and are also profusely given off from the hydrorhiza. Gonothecae similar in both sexes (although sexes not always recognizable with certainty), urn-shaped, bilaterally symmetrical, laterally fl attened; they show their narrowest side when the colonies are seen frontally; on their broadest sides, they are provided with 6-7 convex, rounded crests, more curved distally, and comparatively less arched basally; the narrowest sides show the same crests, but they are concave therein; distally, a dome-shaped protuberance bearing apically the aperture; ca six large, ovoid oocytes per gonotheca.

Remarks
Through its fascicled stems and distinctive gonothecae, this species comes close to S. hians (see above) and the material incorrectly assigned by Vervoort & Watson (2003) to S. protectum (see above). No other nominal species, besides S. hians and S. rectangulatum sp. nov., are known to possess fascicled stems. The differences between these two hydroids could be noted in Fig. 8. It should be noted that, as stated above, Vervoort & Watson's material possibly comprises a mix of species, of which one (NZOI P34, slide 2225) has proportionally longer hydrothecae than S. rectangulatum sp. nov., and seems therefore specifi cally different, while the other (NMNZ BS904, slides 4285) has shorter hydrothecae, and could also belong to another species.

Description
Colony arising from tortuous, branching, anastomosing hydrorhiza creeping on antipatharian host. Stems erect, up to 1 cm high, monosiphonic, unbranched or with, at most, single side branches; proximal part of varied length, though short, ahydrothecate, with smooth perisarc, and basal constriction above origin from stolon; above, remainder of stem hydrothecate, divided into a regular succession of moderatelylong internodes through oblique constrictions of the perisarc slanting in alternate directions, more conspicuous distally; each internode relatively short, widening distally, where it bears a hydrotheca. Side branches, when present, of varied length, given off laterally from below the base of a stem hydrotheca through indistinct apophysis; structure similar to that of stem, except for the fi rst internode that is comparatively longer than subsequent ones. Hydrothecae in two coplanar rows on both stems and branches, alternate, immersed for ⅓ or less into their corresponding internodes; tubular, strongly curved outwards from internode (at nearly right angle), perisarc smooth throughout; proximal abaxial wall distinctly swollen, then straight to slightly concave in middle; free adaxial wall convex, collapsed on distal half over abaxial wall, leaving two broad, lateral 'wings' forming a gutter-shaped aperture; the latter, slightly everted distally on abaxial side, rim occasionally bearing 1-2 renovations; adnate adaxial wall convex, ending basally in perisarc plug; there is no hydrothecal base; opercular apparatus not clearly discernible, but likely composed of one adaxial fl ap. Hydranths badly-preserved, though there is no evidence of an abaxial caecum; tentacle number could not be ascertained. Gonothecae not observed.

Remarks
This is a very delicate, small species, with sparingly-branched stems and strictly alternate hydrothecae, distinctly curved outwards, adnate for (at most) ⅓ of their adaxial length. There are only three congeners displaying an alternate arrangement of their hydrothecae, namely: D. inornata Nutting, 1927, D. nuttingi Stechow, 1913, and D. paarmani Nutting, 1904 However, D. inornata from the Philippine region forms rather tall (7.5 cm high), pinnate colonies, and its hydrothecae are deeply immersed, leaving only about ¼ of their adaxial wall free from the internode (Nutting 1927). In the Japanese D. nuttingi, the hydrothecae are adnate for less than half their length, and their free parts point "obliquely upwards, not bending"; in addition, their wall is provided with fi ve longitudinal ridges: two latero-adaxial, two lateral and one abaxial (Hirohito 1995). The western  (2019) Atlantic D. paarmani forms large (7.6 cm high), pinnate colonies (Nutting 1904); stem hydrothecae "are arranged in pairs basally but gradually, towards the top part of the colony, they become sub-alternate", although the cladial ones are always alternate (Vervoort 1972). The thecae are free for only ⅓ from their corresponding internodes, and curve only gently outwards (Nutting 1904).

Remarks
The mode of branching is characteristically trifi d: each stem gives rise basally to two opposite side branches that become secondary stems; each of these gives rise again, from below their basalmost pair of hydrothecae, to an opposite pair of 2 nd order branches, and the process is repeated again until 4 th order branches are obtained, as observed in material MNHN-IK-2015-401.

Distribution
Philippines, Japan, New Caledonia, Vanuatu, Fiji and Tonga (Galea 2016).  Table 6 Diagnosis Stems simple, monosiphonic, bearing pinnately-arranged hydrocladia in opposite pairs. Division into internodes irregular; each internode with a pair of indistinct apophyses supporting cladia and their associated axillary hydrothecae, as well as 0-3 pairs of hydrothecae below. Cladia divided into more or less regular internodes comprising 0-3 pairs of opposite hydrothecae. Hydrothecae tubular, deeply immersed into internode, not contiguous, aperture facing outwards, provided with two lateral, triangular cusps. Gonothecae unknown.

Description
Colony erect, 3.8 cm high, stiff when out of liquid, arising from creeping, branching hydrorhiza; stem monosiphonic, unbranched, composed of a short (3.5 mm long), athecate, basal part above the origin from stolon, and a much longer, distal thecate and cladiate part; the latter divided into irregular internodes by means of transverse constrictions of the perisarc; each internode long, composed distally of a pair of axillar hydrothecae above the insertion of two opposite cladia, as well as 0-3 pairs of hydrothecae below; hydrothecae opposite and distant from each one within a pair. No distinct stem apophyses supporting the cladia; successive pairs of cladia distant of 1.5-4 mm, depending of the number of intervening pairs of hydrothecae; cladia up to 1.3 cm long and comprising up to 16 pairs of successive hydrothecae; divided by transverse nodes, occasionally indistinct, into rather irregular internodes, generally comprising a single pair of hydrothecae distally, although 2-3 of these may occur elsewhere; fi rst, proximal most internode comparatively longer than subsequent ones. Hydrothecae in strictly opposite pairs, not contiguous, GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia though much closer to one another compared with their cauline counterparts; almost tubular, gently curving outwards, deeply immersed into the corresponding internode, leaving 1/6-1/7 of their adaxial wall free; the latter consequently short and distinctly concave; adnate adaxial wall concave; abaxial wall slightly curved outwards, especially distally; margin thickened, provided with two conspicuous, lateral, triangular cusps with rounded tips; opercular apparatus lost. Hydranths badly-preserved, presence of an abaxial gastric diverticulum could not be ascertained. Gonothecae absent. Perisarc of the colony thick and brown.

Remarks
According to Galea & Ferry (2015 : 230-231, ta ble 2), only two nominal species of Dynamena described so far form pinnate colonies with opposite cladia, namely D. anceps (Fraser, 1938) and D. japonica Stechow, 1920. Through the court esy of D. Geiger of the Santa Barbara Museum of Natural History (SBMNH), CA, USA, one of us (H.R.G.) was able to see several macrophotographs of the lecto-and one of the paralectotypes of D. anceps, demonstrating that it is a much slenderer species, with hydrothecae free from their corresponding internodes for a much longer portion than in D. opposite sp. nov.

Distribution
Only known from off New Caledonia (present study).
Genus Geminella Billard, 1925 Geminella ceramensis (Billard, 1925) Geminella ceramensis -   Table 7 Diagnosis Stems helicoidal, giving raise laterally to secondary branches with pinnate arrangement of cladia. Nodes mostly indistinct, but equivalents of internodes comprising a proximal apophysis (supporting a cladium) and its associated axillar hydrotheca, two alternate hydrothecae above, and a second, distal apophysis together with its axillar hydrotheca. Stem hydrothecae relatively distant, shifted on to the anterior side, small, deeply-immersed into internodes; cladial hydrothecae closely-set, large, adnate for less than half their adaxial length, strongly projecting outwards in opposite directions. Gonothecae borne below the bases of axillar stem hydrothecae; exceedingly long, club-shaped, aperture distal, rounded, borne on recurved (at right angle) apex of gonotheca.

Description
The holotype comprises the apical part of a fertile colony; its lightly fascicled stem was obviously branched in open spiral throughout the colony, but only the three distalmost secondary branches subsist, each of which displays a pinnate arrangement of its hydrocladia. The paratype is equally devoid of its very proximal part comprising the hydrorhiza, but possesses a much longer (9 mm) proximal portion of its stem above the origin from stolon; the main tube, accompanied by a couple of accessory counterparts, is repeatedly divided (by transverse nodes) into short segments, each of which bears a hydrotheca and, occasionally, a lateral apophysis immediately below (its associated hydrotheca thus becoming axillar), carrying the stump of a branch. Remainder of stem gives rise to four side branches arranged helicoidally and having pinnately-inserted hydrocladia. Branches, given off in either anti-clockwise (holotype) or clockwise (paratype) manner, composed of a short, quadrangular segment, a succession of 3-4 alternate hydrothecae, and a much longer, regular, hydrocladiate part. The latter, displaying a mostly indistinct GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia  (2019) division into internodes, is composed of a short, lateral apophysis, an axillar hydrotheca associated to it, two alternate hydrothecae above, and a second lateral cladial apophysis on opposite side, together with its corresponding axillary hydrotheca; cladia alternate along the branch. Apophyses short, each supporting a cladium, from which they are separated through straight nodes; the two rows of apophyses not coplanar, but shifted upwards; cladia divided into thecate internodes through transverse constrictions of the perisarc; there is a short, quadrangular segment proximally; each internode with generally two, occasionally three, hydrothecae, although 1 st internode bearing usually an increased number of hydrothecae, reaching as many as six. Two types of hydrothecae occur within the colony: cauline and cladial, differing much in their morphology. Cauline hydrothecae relatively distant from each other, small, slender, deeply immersed into internodes, with only a short free adaxial part left; tubular, with thick perisarc, free part curved outwards, rim rounded, slightly everted, occasionally renovated once, with no trace of opercular apparatus. Cauline hydrothecae and cauline apophyses distinctly shifted on to the 'anterior' side of the stem. Cladial hydrothecae large, tubular, adnate for less than half their length to their corresponding internodes; successive hydrothecae closely-set, free parts strongly projecting outwards in opposite directions; perisarc thin, fi nely and densely striated; aperture tricuspidate, with an adaxial and two latero-abaxial cusps; abaxial cusps separated by a shallow embayment, while deep, rounded embayments occur between the adaxial and latero-abaxial cusps; opercular apparatus composed of three triangular valves: two latero-adaxial, and a much wider abaxial one; hydranths with 10-12 fi liform tentacles; no caecum. Gonothecae given off from below the hydrothecal bases of cauline axillar hydrothecae; club-shaped, exceedingly long, perisarc fi nely and densely-striated especially on upper half, becoming smooth basally, apex of gonotheca curved abruptly outwards and there carrying a large, rounded aperture; sex could not be ascertained. None of the nominal species mentioned above displays such strongly bimorphic hydrothecae and forms such exceedingly elongate, club-shaped gonothecae as H. clavaformis sp. nov. Indeed, the gonothecae of the poorly-known H. distans and H. plumulifera were described by Nutting (1904) and Jäderholm (1896), respectively, while those of the well-known H. falcata are dealt with, among others, by Cornelius (1995). All are short, broadly ovoid, tapering basally, with a round, distal aperture on top of a short neck region. Only specimens of H. franciscana without gonothecae are known to date.
Unlike its congeners, the new species possesses an opercular apparatus composed of three triangular fl aps meeting centrally to form a low pyramidal roof. Vervoort (1993: 185) debated on the composition of this structure (presence of either a single adaxial fl ap, or of a larger adaxial and a smaller abaxial one, according to the statements of different authors), and concluded that two fl aps occurred in the Atlantic material at his disposal.
Despite these morphological peculiarities, the present species is provisionally accommodated within the genus Hydrallmania Hincks, 1868, on the account of its mode of branching and the unilateral arrangement of the side branches and hydrothecae, pending the availability of additional material suitable for molecular analyses expected to confi dently clarify its correct systematic position.

Distribution
Only known from off New Caledonia (present study).

Remarks
Unlike stated by Watson (2000), the gonothecae in the present material are pro vided with a short, tubular pedicel.

Remarks
Colonies of reticulate appearance, formed through anastomoses of terminal tendrils on neighboring branchlets, are met with in material MNHN-IK-2015-440. Tendrils may also settle down on main stems, forming accessory tubes. Abortive branchlets, given off from below the hydrothecal bases, may never develop hydrothecate internodes, transforming directly into tendrils that reach other hydrothecal bases, uniting laterally neighboring side branches, as illustrated by material MNHN-IK-2015-409. Despite the abundance of the material available both earlier (Vervoort 1993) and in the present collections, the gonothecae of this species have yet to be discovered.

Distribution
New Caledonia, Norfolk Ridge and Solomon Islands (Galea 2016

Remarks
The colonies are fl abellate, with no defi nite main stem, as this branches many times, fi rst branching occurring a short distance after its origin from stolon. The stem and side branches are strongly fascicled, tending gradually to monosiphonic distally. The hydrothecae are provided with 14-16 transverse ridges, while Galea (2016) reported hydrothecae with 19-21 ridges in material from New Caledonia examined so far. The gonothecae, ca 2790 μm long and 1570 μm wide (only one measured), display 6-8 broad transverse ridges; in one colony with three gonothecae, there are 4-6 apical spines surrounding the aperture; in two other colonies, each with but one gonotheca, seven and eight spines could be found, respectively, demonstrating that in the New Caledonian population, at least, their number is inconstant, and ranges from four to eight.
GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia Galea (2016) pointed out morphological and morphometrical differences in materials studied by various authors, notably the condition of the stem, the number of hydrothecal ridges, and the size of gonothecae. The latter, in the present material, are the largest ever reported in this species, while Vervoort & Watson (2003) found 1720-1935 μm long and 1230-1280 μm wide gonothecae, although even smaller ones occurred in material studied by Hirohito (1995) (750-800 × 550-700 μm).
A more comprehensive study, based on materials of different origins, is needed to understand the variations reported so far in the literature.

Remarks
In material MNHN-IK-2015-426, the perisarc of the colony may be wavy to wrinkled in places, and the corrugations of the hydrothecae are more conspicuous, encompassing also their abaxial wall.
The hydrothecae in sample MNHN-IK-2015-419 display seven internal projections of the perisarc: four latero-adaxial, of which the two adaxial-most are the most prominent, one large abaxial, and two smaller latero-abaxial (Fig. 14D). Its gonothecae are believed to be male, owing their shape and size (ca 1680 μm long and 505 μm wide, only one measured), compared to those from the holotype (see Galea 2016); they are given off laterally from the middle of the internode on side opposite to hydrotheca but, soon after, they are shifted on to the anterior/posterior side of the colony; club-shaped, with slightly undulated walls, aperture distal, rounded, small (ca 100 μm wide), borne on rather short and narrow neck region.

Remarks
The gonothecae of this distinctive species are still to be discovered.

Remarks
The present material agrees in nearly all details with the description given by Vervoort & Watson (2003) of this species. However, some colonies have their stems and the basal part of their lower branches lightly but distinctly fascicled. In addition, examination of many gonothecae (from different colonies) seen in apical view showed that the external ridges are not always spirally arranged, as stated by Vervoort & Watson (2003), but they also form concentric ridges that are perfectly transverse in lateral view. All gonothecae agreed with the supposedly female ones described by these authors, but had up to 14 ridges in material MNHN-IK-2015-405 and up to 20 in material MNHN-IK-2015-406, although any  (2019) other morphological difference could be noted (e.g., a slenderer appearance, as in the supposedly males described by these authors).
The 16S data (see Fig 20 and the 'Molecular study' section) strongly suggest that this species belongs to the Symplectoscyphidae, and not the Sertularidae in the sense of Maronna et al. (2016).

Etymology
The specifi c name combines two Latin words 'ăcūtus, -a, -um', meaning 'sharp', and 'strĭātus, -a, -um', meaning 'provided with striae', to describe the particulars of the transverse ridges of the outer hydrothecal wall.

Description
Colonies arising from creeping, branching, anastomosing hydrorhiza. Stems erect, monosiphonic, up to 2.5 cm high, composed of a basal, smooth, ahydrothecate part, 3-7 mm long above origin from GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia stolon, and a much longer, distal, hydrothecate part above; the latter divided into regular internodes by means of almost indistinct oblique nodes slanting in alternate directions; branching sparse, with up to three coplanar side branches given off laterally and irregularly from below the bases of some stem hydrothecae, on one or both sides of the stem; branches with similar structure to that of the stem. Internodes relatively short, distinctly geniculate, each bearing distally a hydrotheca; the latter alternate GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia in position, the two rows being coplanar. Hydrothecae moderately-long, conical, adnate for ⅓ or less to the corresponding internodes; surface conspicuously ridged; ridges well-developed, projecting apically almost as free frills; there are 7-8 complete ridges encircling the hydrotheca distally, and up to 8-10 on the abaxial wall, the basalmost ones incomplete; there are seven intrathecal, submarginal projections of the perisarc, visible in the lower stem hydrothecae, but disappearing towards distal parts of the colony: two latero-adaxial, one abaxial, and two latero-abaxial. Gonotheca borne on stems and/or branches, given off laterally in middle of internode on side opposite to hydrotheca; large, piriform, transversely-ridged (12-14 ridges), tapering abruptly basally into indistinct pedicel, distally walls merging progressively; aperture apical, small, rounded, on short neck region with broadly polygonal perimeter, occasionally forming 3 indistinct projections of perisarc.

Remarks
The prominent ridges on the outer walls of the hydrothecae are distinctive. Only a few congeners are provided with transverse undulations or ridges (see Table 9 for comparison), but in none their development reaches the extent met with in S. acutustriatus sp. nov.
The internal, submarginal cusps are variably present among the hydrothecae belonging to the same stem (e.g., MNHN-IK-2015-460), and are even absent in stems of some colonies (e.g., MNHN-IK-2015-446). Only a few congeners have been shown to possess such structures, and their main distinguishing features are summarized in Table 10.
The systematic position of this species is discussed in the 'Molecular study' section.

Remarks
A small species, with minute hydrothecae resembling those of S. ralphae Vervoort, 1993 through their shape and size (compare Fig. 17F with Galea 2016: fi g 10Q-T). Unlike S. commensalis that forms irregularly-branched colonies (up to 2 nd order branches observed), the latter builds regularly-pinnate colonies. In addition, their respective gonothecae are different [compare Fig. 17G with Galea 2016: fi g. 10U-V).

Description
Colony erect, 5.1 cm high, arising from creeping hydrorhiza. Stem monosiphonic, fl accid, unable to support itself when out of liquid; basal 1.6 cm ahydrothecate, with smooth perisarc; remainder of stem divided into regular internodes by means of indistinct oblique nodes slanting in alternate directions; internodes distinctly geniculate, long, each bearing distally a hydrotheca; branching sparse, irregular: only two side branches, neither branching further, occur in the present specimen; they are given off laterally and in opposite directions, from below the bases of two distant stem hydrothecae, and are coplanar. Hydrothecae long, slightly conical, adnate for ⅓ or less to their corresponding internodes; abaxial wall straight for most of its length, imperceptibly convex distally; free adaxial wall slightly sigmoid, convex for most of its length, then concave towards aperture; aperture three-cusped, adaxial cusp slightly produced, latero-abaxial cusps less prominent, with rounded tips, separated by wide, shallow embayments; operculum composed of three triangular fl aps meeting centrally to form a pyramidal roof; 8 internal, submarginal projections of the perisarc: one minute adaxial, two pairs of latero-adaxial, one large abaxial, and two latero-abaxial. Gonothecae not observed.

Remarks
The present material fi ts the description and illustrations given by Vervoort (1993) of S. paulensis. It is mainly characterized by 1) its rootlike hydrorhiza, fi rmly adhering the colony to a hard substrate; 2) the stem is unbranched but fascicled, tending to monosiphonic distally; 3) the internodes are weakly indicated, and composed of a minute apophysis (supporting a cladium) together with its associated axillar hydrotheca, as well as two alternate hydrothecae above; 4) the cladia are given off regularly in an alternate manner; unbranched, up to 3 cm long, composed of up to 26 hydrothecate internodes separated by weak oblique nodes; 5) the gonothecae are laterally fl attened, with undulated walls; aperture rounded atop of a neck region borne on a terminal, slightly depressed plateau; likely female, containing 1-2 large, ovoid bodies. El Beshbeeshy (2011) created S. vervoorti for material studied earlier by both Vervoort (1972, as S. paulensis) and Stepanjants (1979, as Sertularella paulensis), on the account of 1) wider internodes and nodes; 2) hydrothecae circular in cross section and isodiametric throughout; 3) hydrothecal aperture everted, rim provided with pointed cusps. However, in light of the reexamination of the lectotype of S. paulensis by Vervoort (1993: fi g. 43A-D) and the comparative measurements given in Table 11, this doesn't seem justifi ed. Indeed, Vervoort (1993: 263) clearly stated that the "Valdivia material is in perfect agreement with specimens described by Vervoort (1972: 180-183, fi gs 60b, 61)".

Remarks
In view of the present material, always fertile, it can be now stated that the gonothecae are sexually dimorphic, as suspected earlier by Galea (2016). Female gonothecae are longer and larger, and possess a larger number of transverse ridges, and a comparatively wider terminal funnel.

Description
Colony arising from a root-like, ramifi ed hydrorhiza fi rmly anchoring it to its substrate. Stem simple, 6.5 cm high, fascicled over its proximal 2 cm; divided by weakly-indicated transverse nodes, each internode composed of an indistinct apophysis (supporting a cladium) with its associated axillary hydrotheca, and two alternate hydrothecae above. Cladia generally alternate, but there can be exceptions especially when one, three or four hydrothecae (instead of only two) occur above an axillar hydrotheca. Cladia given off slightly laterally from below the bases of stem hydrothecae, and distinctly shifted on to the 'anterior' side of the colony; up to 1.8 cm long and carrying up to 15 hydrothecate internodes separated by distinct oblique nodes; generally unbranched, though one cladium bears three short, secondary branchlets of up to six hydrothecate internodes. Hydrothecae alternate, large, tubular, adnate for about 2/ 7 to the corresponding internodes; free adaxial wall long, convex proximally, concave distally; adnate adaxial wall slightly curved, ending basally in conspicuous perisarc plug; there is no hydrothecal base, the abaxial wall being a continuation of the internode; aperture circular in frontal view, rim everted on adaxial side, provided with three broad, low, triangular cusps separated by shallow embayments; opercular apparatus composed of three triangular fl aps meeting centrally to form a pyramidal roof. A single gonotheca arises from below the base of a cladial hydrotheca, but it is incomplete, having only its basal, vasiform part already formed.

Remarks
The present material comes close to that assigned by Billard (1925) to Symplectoscyphus tropicus (Hartlaub, 1901), although it is of slightly bigger proportions, and doesn't have fully-formed gonothecae so as to facilitate their comparison. In addition, it is not clear whether this record and that of Billard belong to the same species as the material of Clarke (1894), especially since there are no available measurements for the latter. However, the gonothecae illustrated by both Billard and Clarke appear very similar in shape, supporting a possible conspecifi city. Hartlaub (1901) noted the secondary homonymy between Sertularia variabilis (Clarke, 1894) and Sertularella variabilis Bale, 1888, and renamed the former Sertularella tropica. Both Clarke's and Bale's hydroids should be correctly assigned to the tricuspidate genus Symplectoscyphus. In addition, the latter is now considered as a junior synonym of Symplectoscyphus indivisus (Bale, 1882) (Vervoort & Watson 2003).

Diagnosis
Stems unbranched, strongly fascicled basally, arched downwards distally, and there giving rise to a row of cladia arranged unilaterally; division into internodes indistinct; each equivalent of internode with short, lateral apophysis supporting a cladium, an axillar nematotheca and second nematotheca on opposite side and slightly above; cladia divided into moderately-long internodes, each bearing a hydrotheca distally; the two rows of hydrothecae forming a sharp angle; hydrothecae long, tubular,  (Hartlaub, 1901), in μm.

Present study
Billard (

Remarks
The genus Tuberocaulus gen. nov. is monotypic so far and comprises Tuberocaulus scorpioides (Vervoort, 1993) gen. et comb. nov. This species was originally placed in Thyroscyphus Allman, 1877 on account of the attachment of the hydranth to the inner hydrothecal wall (whose surface is lined by "a sheath of tissue" = mantle) "by means of a circular fold". However, unlike Thyroscyphus, the hydrotheca of this species is given off from the internode, and it is not borne on a distinct apophysis; additionally, it has a well-defi ned (though short) adnate adaxial wall, as well as a base (see description above).
The fascicled condition of the stem and its peculiar appearance, the presence of what appears to be stem nematothecae, as well as the unilateral arrangement of cladia and their hydrothecae, are not features shared by the genus of Allman (1877).
The systematic position of T. scorpioides could not be ascertained on morphological grounds alone. Indeed, its long, tubular, tricuspidate hydrothecae superfi cially recall those of Parascyphus simplex (Lamouroux, 1816), but in that species, the thecae are borne on distinct stem apophyses, their 'bases' are represented by an internal annular thickening of the perisarc, and the marginal cusps adopt a different position (one adaxial and two latero-abaxial cusps, see Galea et al. 2014).
Being fused to the corresponding internodes, the hydrothecae of T. scorpioides are reminiscent of those met with in members of the Sertulariida Maronna et al., 2016(with only Gonaxia Vervoort, 1993 showing the same position of the marginal cusps), although nematothecae have never been reported in any genus belonging to it.
The relationship of Tuberoscyphus gen. nov. to the other Leptothecata families remains to be investigated by molecular phylogenies. In the absence of such studies for the time being, the genus is left provisionally in the Thyroscyphidae.

Description
Colony erect, 6.5 cm high, relatively stiff when out of liquid, arising from much branched, rhizoid hydrorhiza fi rmly attached to the substrate. Stem simple, strongly fascicled proximally, grading to monosiphonic 4 cm after its origin from stolon. Main tube composed of a long, straight, proximal part devoid of cladia and having irregularly wrinkled to smooth perisarc, and a comparatively shorter, distal part bearing hydrocladia, distinctively curved downwards. Proximal part undivided, except for a distal, short, quadrangular segment separating it from the distal hydrocladiate part through two broad, conspicuous transverse nodes; basal and quadrangular segments provided distally with large, prominent nematothecae with distinct, apical, rounded aperture (Fig. 18A, arrowheads). Hydrocladiate part divided into internodes through transverse constrictions of the perisarc, distinct basally, becoming obsolete distally. Each internode comprises a short, lateral apophysis (supporting a cladium), an axillar nematotheca, as well as a second, lateral nematotheca in middle of opposite site; all apophyses given off on same side of the stem. The two rows of stem nematothecae distinctly shifted on to the 'anterior' side of the colony in the lower portion of the hydrocladiate part of the stem, becoming gradually almost coplanar distally; similarly, the cladia adopt a more lateral arrangement along the stem towards its distal end. Axillar nematothecae tubular on proximal portion of the hydrocladiate part of the stem, becoming mere mamelons distally; no distinct aperture could be noted on any of them. Nematothecae in opposite row comparatively less prominent, resembling mamelons in shape, provided occasionally with slit-like aperture in axil formed with the corresponding stem internode (Fig. 18A, C, arrowheads). Cladia distant of 1-1.5 mm, up to 2 cm long, divided into up to 18 thecate internodes by means of transverse nodes; proximal most internode comparatively longer than subsequent ones; internodes moderately long, each provided with a hydrotheca distally. Hydrothecae alternate but conspicuously shifted on to the upper side of cladia, the two rows forming a very acute angle; long, tubular, lower halves gradually tapering GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia basally, adnate to the internode for a minute portion of their adaxial wall; distally, a large, circular aperture surrounded by three prominent, pointed, triangular cusps (one abaxial, two latero-adaxial) separated by large, deep, rounded embayments; rim thickened; a perisarc plug extending downwards the adnate adaxial wall of hydrotheca at junction with its base; a rounded fenestra below the base, as attachment site for the gonotheca. Hydranths large, attached to lower ¼ of inner hydrothecal wall, provided with ca 16-20 fi liform tentacles. Gonothecae club-shaped, with large, semi-circular, subterminal aperture, in a rounded depression in the gonothecal wall on side facing the hydrotheca. Perisarc of both hydro-and gonothecae almost fi lmy and easily collapsible, explaining why so many of those are partially or totally broken. Vervoort (1993) noted "perisarcal protuberance[s]" in the axil formed by the cladia with the stem, but not on the opposite side of the stem internodes, and did not comment on their signifi cance. These structures, occasionally showing distinct apical apertures, or apertures in the axil formed with the stem internodes, are thought to be nematothecae, although an accumulation of nematocysts could not be confi rmed in this material with badly-preserved coenosarc.

Distribution
Only known from off New Caledonia (Vervoort 1993;present study

Diagnosis
Colonies fl abellate, with much branched, heavily-fascicled stems. Division into internodes indistinct, but equivalents of internodes with a proximal cladial apophysis and its associated axillary hydrotheca, two alternate hydrothecae above, and a second cladial apophysis, given off on side opposite to the preceding one; hydrothecae long, tubular, with slightly everted, circular margin, tapering in lower third into long, proximally annulated pedicel. No nematothecae on the hydrothecal apophyses. Gonothecae aggregated into long masses of coppinia around the side branches, but neither fused, nor appressed against each other; long, tubular, walls slightly wrinkled, basally tapering into minute pedicel, distally truncate.

Description
Colonies fl abellate, up to 10.5 cm high, arising from root-like hydrorhiza, fi rmly attached to the substrate. Main stem branched irregularly, with up to 5 th order side branches; stem and branches heavily fascicled for most of their length, grading to monosiphonic distally; stems up to 3 mm thick basally. Perisarc dark in fascicled parts, brownish in monosiphonic ones. Stem divided into indistinct internodes with the following sequence: a prominent, proximal apophysis (supporting a cladium) and its associated axillary hydrotheca (itself borne on a short, distinct apophysis), followed by two alternate hydrothecae above (each borne on a short stem apophysis), and a second, distal, apophysis (supporting following cladium), together with its associated hydrotheca (itself borne on a stem apophysis). Cladia alternate, monosiphonic, divided through generally indistinct, slightly oblique nodes into moderately-long internodes bearing distally a short apophysis supporting a hydrotheca; apophyses alternate, coplanar; cladia with up to 13 hydrothecate internodes; fi rst internode with a couple of spiral twists basally. Hydrothecae borne on relatively long pedicels, invariably annulated basally (usually two, but up to four annuli observed), but also distally (0-4 annuli), occasionally in middle. Hydrotheca cup-shaped, elongated, proximal ⅓ tapering gradually below, distal ⅔ tubular; aperture circular, rim slightly but distinctly everted, margin smooth; perisarc thin and smooth; hydrotheca delimited basally from pedicel by thin diaphragm. Hydranths with ca 16 fi liform tentacles, with no caecum. Nematothecae absent throughout. Gonothecae grouped in certain parts of the colonies, but independent from each other (neither contiguous, nor fused), arising from accessory tubes of the side branches; long, tubular, slightly curved in middle part, tapering below, distally truncate, walls undulated, perisarc rather thick and dark brown. No nematophorous ramuli amongst the gonothecae.
[…] In frontal aspect each gonangium is a little narrowed in near the distal end and then widens outwards forming a conspicuous round projection or shoulder at each side of the top where the gonangium reaches its maximum width. These shoulders are produced slightly downwards into truncated processes, each of which ends in a small circular aperture directly facing towards the proximal extremity of the gonangium" (Briggs 1922) Z. convallaria (Allman, 1877) "Hydrothecae usually borne on one side of hydrocaulus, facing a plane perpendicular to the plane of the branches […] "bending near distal end to varied extent, occasionally at a right angle […]. Nematothecae present on tubes of stem and branches, on apophysis or on rare occasions on the internodes" (Hirohito 1995). Gonothecae independent from each other, "anchor-shaped, apex with two downwardly directed fl ukes, at the of which is an opening. Protective ramules with some nematothecae occasionally present" (Rees & Vervoort 1987) Z. elongata Ramil & Vervoort, 1992 "Hydrothecae […] directed frontally, tubular, placed on pedicel of considerable length […]. Adcauline hydrothecal wall distinctly convex and abcauline wall concave, giving hydrotheca a characteristic, curved appearance.
[…] Nematothecae inserting on apophyses, one on each side of hydrothecae, on base of side-branches (hydrocladia) and dispersed on axis and secondary tubules.
[…] Gonothecae separate, without adnate walls, ovoid, apically with bifurcate process, bifurcations ending in gonothecal apertures, two for each gonotheca" (Ramil & Vervoort 1992) Z. infundibulum Millard, 1958 "The two rows of hydrothecae on stem and branches not in the same plane, but shifted on to the anterior surface and forming a sharp angle (about 15-40°) between them". Hydrotheca "elongated, curving upwards in the distal part, with abcauline wall convex, and adcauline wall convex in proximal two-thirds and concave in distal third.
[…] One nematotheca on the apophysis next to each hydrothecal pedicel" (Millard 1958). "Gonothecae not adpressed, narrow at base and widening distally, then divided into two outwardly curved necks bearing the terminal apertures. Protective tubular structures numerous, arising amongst the gonothecae and rising above them, completely obscuring them and forming a bristly coat to the coppinia; each branching irregularly and bearing many nematothecae similar to those of the trophosome" (Millard 1980 (Vervoort & Watson 2003).
The differences to Z. niger sp. nov. of the congeners displaying both hydrothecae borne on long pedicels and separate, loosely-aggregated gonothecae, are summarized in Table 14.
[…] Nematothecae inserting on apophyses, one on each side of the hydrothecal pedicel.
[…] Gonothecae ovoid, aggregated though not adnate, at distal extremity with two or three short, tubular processes, pointing obliquely upwards, each with one terminal aperture" (Ramil & Vervoort 1992) Z. levinseni (Saemundsson, 1911) "apophyses alternately directed obliquely left and right and frontally, on which insert the hydrothecae that consequently are also frontally directed and are not placed in the same plane […]. Hydrotheca on fairly long pedicel […] tubular, slightly asymmetric as adcauline wall is slightly convex and abcauline wall slightly concave.
[…] Nematothecae inserting on apophyses, usually one on each side of hydrothecal pedicel […]. Coppiniae […] composed of dense aggregations of individual, non-adnate gonothecae. Each gonotheca ovoid, slightly laterally compressed, distally produced into a pair of laterally curved tubes" (Ramil & Vervoort 1992) Z. pinnata (G.O. Sars, 1874) Hydrothecae "bell-shaped to tubular, rather deep, tapering in lower third, often with slight asymmetric bulge imparting pseudo-bilateral symmetry; always roughly straight on outer side […]; pedicel continuing tapered outline of hydrotheca, varied in length, sometimes with annulus, and many with rather deep fold on adjacent side just above axil. No nematophores or nematothecae" (Cornelius 1995). Coppinia "composed of closely packed, but not coalesced, gonothecae without protective nematophorous ramuli. Gonothecae elongate, sac-shaped bodies, apically with 2-4 circular openings at end of short funnel" (Rees & Vervoort 1987) Z. sibogae Billard, 1919 Hydrothecae shifted on frontally, distinctively curved in middle, "with deep constriction on adcauline side"; "nematothecae present on peripheral tubes, singly on each lateral side of each apophysis, on rare occasions on hydrothecal pedicel"; gonothecae "pouch-like, bearing one or two long tubes at the distal end; tubes facing to various directions" (Hirohito 1995). "Gonothecae loosely aggregated in coppinia on stem, gonothecae not adnate, shape very irregular sac-shaped […], with 1-3 openings on tubular extensions. Coppinia comprise also protective branches, branched, forming canopy over gonothecae, with nematothecae" (Schuchert 2015) Z. stechowi (Jäderholm, 1919) Trophosome poorly described by Jäderholm (1919). Hydrothecae alternate, coplanar, borne on moderately-long, wrinkled to occasionally ringed pedicels; hydrothecae long, almost tubular, tapering basally. Gonothecae not contiguous to each other, without nematophorous tubules, slender, T-shaped, distally with two opposite apertures (Hirohito 1995) Z. unilateralis Totton, 1930 "Hydrothecae more or less unilateral […] relatively longer than pedicels"; curved, apertures "facing both upwards and outwards, so that those of one side are at right angles to those of the other "; nematothecae "one on the outer side of each stem or branch apophysis at base of hydrothecal pedicel" (Totton 1930). "Though the gonothecae touch they are not compressed but have open spaces in between, from which abundant nematophorous ramules project. Each gonotheca sac-shaped, swollen and more or less oval to round in outline. Apex with 3 laterally projecting, short funnels, slightly fl ared at the rim, openings directed variously" (Rees & Vervoort 1987) (2019) The trophosome of Z. tottoni Rees & Vervoort, 1987, a species from off Oman with a so far unknown gonosome, shows a few similarities to that of Z. niger sp. nov., notably the mode of branching of its stems, the shape of its hydrothecae, and the presence of rather long hydrothecal pedicels. However, the latter does not possess proximally the distinctive basal annuli, its hydrothecae are comparatively shorter and narrower, and there is one nematotheca on frontal side of each apophysis supporting a hydrotheca (Rees & Vervoort 1987).

Distribution
Only known from off New Caledonia (present study).

Molecular study
For 30 samples described in this study it was possible to obtain about 600 bp of the mitochondrial 16S gene sequence that could be compared in a maximum likelihood tree (Fig. 20). All sequences were initially compared to all GenBank sequences using BlastN (Johnson et al. 2008). This allowed to control whether each new sequence was, indeed, of hydrozoan origin, and concomitantly identifi ed closelyrelated sequences that proved important for subsequent comparisons. A total of 90 sequences were thus aligned and used to determine the optimal probabilistic model of sequence evolution, as well as to make the phylogenetic analyses. The optimal substitution model suggested was GTR+I+G. There was no need to remove regions with uncertain alignments, as there were few such regions, and their exclusion did not alter the results signifi cantly. The resulting maximum likelihood tree has numerous unresolved basal nodes, but several families appear in well supported clades (> 70% bootstrap support: Syntheciidae, Symplectoscyphidae, Lafoeidae, Sertularellidae, Staurothecidae, and Zygophylacidae). The family Sertulariidae sensu Maronna et al. (2016) appears also as clade, but with insuffi cient bootstrap support (58%).
Taxonomically noteworthy results are as follows: -two species of Caledoniana and two of Solenoscyphus are more closely-related to the Staurothecidae than to Sertulariidae. Only Solenoscyphus decidualis mapped outside the Solenoscyphus and Staurothecidae clades, but without any supported relationship to other taxa; -Billardia hyalina and B. subrufa (Jäderholm, 1904) (FN424117) are deeply embedded in the well supported Syntheciidae clade; -the four Hincksella species dealt with herein do not group into a common clade, but are scattered over the whole tree. The type species of the genus (H. sibogae; see Totton 1930) associates with Zygophylax, but the node support is not signifi cant; -Dictyocladium reticulatum clusters with the Symplectoscyphidae; -Symplectoscyphus acutustriatus s p. nov. is deeply embedded in the clade Sertularellidae and not in Symplectoscyphidae, the parent taxon of the genus Symplectoscyphus.

Discussion
The principal utility of DNA barcodes (Hebert et al. 2003;Hebert & Gregory 2005), as produced in this study, is to permit a more objective discussion of species identifi cations and also to provide the essential database for future species community analyses via metabarcoding (e.g., Ji et al. 2013;McInnes et al. 2017). Additionally, and if suffi ciently long, they often also permit to obtain phylogenetic trees and to study the evolutionary relationships between clades (Fig. 20). While standard animal barcode sequences are based on COI sequences, this marker proved to be diffi cult or impossible to amplify for some hydrozoan families (Schuchert 2014). The 16S gene has thus gained much more acceptance as a barcode marker for Hydrozoa (Schuchert 2016, and references therein). The 16S marker is a rapidly evolving marker and, as such, not so well suitable for phylogenies at or above the family level. However, well supported clades in a 16S based phylogeny (i.e., bootstrap support > 70%) have so far been confi rmed GALEA H.R. & SCHUCHERT P., Some thecate hydroids from off New Caledonia when additional markers, like 18S or 28S, were included (e.g., Leclère et al. 2009;Maronna et al. 2016). Therefore, the well supported family clades in the present analysis (Fig. 20) are most likely robust enough to be confi rmed by a deeper analysis (study in progress).
The genera Caledoniana and two Solenoscyphus species clearly belong to the Staurothecidae, a family recently separated from the Sertulariidae by Maronna et al. (2016). Morphological features also suggest this reclassifi cation (see above the Taxonomy section). However, some uncertainty remains, as the type species of both genera were not included in the analysis. Moreover, Solenoscyphus decidualis mapped outside the Staurothecidae clade (Fig. 20), but without any supported relationship to other taxa. This does not necessarily mean that S. decidualis is not a member of the Staurothecidae, and more likely refl ects the lack of resolving power of the 16S marker at this taxonomic level. Additional markers are needed to settle down the question. However, considering the long distances of S. decidualis with respect to its congeners, it is almost certain that the former must be classifi ed in a separate, new genus. Until a more comprehensive study becomes available, we prefer to keep the combination Solenoscyphus decidualis for the sake of nomenclatural stability.
According to Maronna et al. (2016), the genus Billardia cannot be placed with certainty within the Leptothecata and it was classifi ed as a "rogue taxon". However, we suspect that this was due to either a misidentifi cation or a sequencing error of one of their samples (KT266603, Billardia subrufa). This sequence clusters with the Symplectoscyphidae (own unpublished results, not shown). Another 16S sequence of the same species available in GenBank (FN424117) has about 13% divergence from KT266603, a value which is clearly too high for intraspecifi c variation. Moreover, the former sample maps within the family Syntheciidae in our analysis. Due to this ambiguity, the sequence KT266603 was not used in the analysis shown in Fig. 20.
Our sequence of Billardia hyalina and that of B. subrufa (FN424117) are deeply embedded in the well supported Syntheciidae clade (Fig. 20). This confi rms the opinion of Cornelius (1982), that Billardia is part of the Syntheciidae.
The four species of Hincksella dealt with herein do not group into a common clade, but are scattered over the whole tree. The type species of the genus (H. sibogae; see Totton, 1930) associates with Zygophylax, but the node support is not signifi cant. An analysis with additional markers is thus needed to resolve accurately their relationships. The genus Hincksella is nevertheless almost certainly polyphyletic. At the species level, however, the data prove that the three species treated here are obviously distinct. In addition, it will be likely necessary in the future to split Hincksella again, and re-validate one of its actual synonyms, Cyclonia Stechow, 1921. The latter was proposed for hydroids recalling Hincksella possessing tubular, largely protruding hydrothecae, similar to those present in H. neocaledonica. The type species of Cyclonia is Cyclonia gracilis Stechow, 1921 (by monotypy), a West-Indian species, now considered as conspecifi c with the Indo-Pacifi c Hincksella pusilla (Ritchie, 1910) (Galea 2010: 20;Galea & Ferry 2015: 236). However, before Cyclonia is resurrected, the type material of its type species must be re-examined and illustrated. Ideally, also 16S sequences from new Caribbean specimens should be obtained and compared to the sequences of Hincksella given herein. Dictyocladium is a rare genus that has not been included in any molecular phylogeny so far. After the splitting of the Sertulariidae in several separate families by Maronna et al. (2016), it was unclear to which family it should belong. Currently, the WoRMS database (Schuchert, 2018) includes it in the family Sertulariidae. In the present dataset, Dictyocladium reticulatum shows a well-supported relationship with the Symplectoscyphidae. The type species of the genus Dictyocladium is Dictyocladium dichotomum Allman, 1888, a junior synonym of D. reticulatum (Kirchenpauer, 1884) (Vervoort & Watson 2003). Our sample is thus representative for the genus. Dictyocladium and Symplectoscyphus have both hydrothecal margins with three cusps at the same position (one adaxial, two latero-abaxial). It seems therefore justifi ed to trasfer the genus Dictyocladium from the family Sertulariidae to the Symplectoscyphidae.
The traditional scope and the relationships of the genus Symplectoscyphus, and its parent taxon Symplectoscyphidae, seem to be more intricate than given in Maronna et al. (2016). Recently, Song et al. (2018), using DNA data, showed that some species of Symplectoscyphus, characterized by gonothecae with spiny processes instead of transverse ridges, do not belong to the Symplectoscyphidae, but to the Sertularellidae, this despite their hydrothecae having three instead of four marginal cusps. For those species, the genus Xingyurella Song et al., 2018 has been created.
We confi rmed the same for an additional species usually attributable morphologically to Symplectoscyphus. While three Symplectoscyphus for which we have new sequence information (S. commensalis, S. ralphae and S. paulensis) unambiguously map within the Symplectoscyphidae (Fig. 20), a fourth, Symplectoscyphus acutustriatus sp. nov., is deeply embedded in the family Sertularellidae. As the species shows no affi nities with the Xingyurella clade, it cannot be simply reclassifi ed as a congener. This apparent confl ict of morphological classifi cation and molecular relationships cannot be confi dently resolved for the time being, and needs a more detailed analysis. It can also not be excluded that some error in the molecular work has occurred, e.g., amplifi cation of a nuclear copy of the 16S gene. However, morphologically speaking, a noteworthy observation is that the hydrothecae of both Xingyurella and S. acutustriatus sp. nov. are Sertularella-like, i.e., conical in shape, not tubular as in most species confi dently assigned to Symplectoscyphus. This character, even taken alone, demonstrates obvious morphological affi nities with the Sertularellidae, instead of the Symplectoscyphidae. It is also interesting to note that the species to which S. acutustriatus sp. nov. is compared in Table 9 display similar conical hydrothecae; in addition, they possess barrel-shaped, transversely-ringed gonothecae, with no distinct apical funnel bearing the aperture, the latter being occasionally surrounded by a few projections of the perisarc, also recalling hydroids of the genus Sertularella. Pending a corroboration of the results with additional markers, we prefer to use the combination Symplectoscyphus acutustriatus sp. nov.