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

Sixteen aglaopheniid hydroids occurring in two recent, deep water collections from off New Caledonia are reported upon, of which 8 species are new, namely Cladocarpus asymmetricus sp. nov., C. partitus sp. nov., C. pennatus sp. nov., Lytocarpia fragilis sp. nov., L. pilosa sp. nov., L. pseudoctenata sp. nov., L. subtilis sp. nov. and Macrorhynchia spiralis sp. nov., the latter producing medusoid gonophores. Although not occurring in the present collections, brief notes on M. disjuncta (Pictet, 1893), including the fi rst description of its gonosome, are provided to support its specifi c separation from M. phoenicea (Busk, 1852).


Introduction
This is the second report of a developing series dealing with the hydroids collected during the KANACONO (2016) and KANADEEP (2017) expeditions of the French Tropical Deep-Sea Benthos Program.
As noted by Watson (2002), A. sinuosa is easily recognizable through the sinuous bends at intervals along the stem that mark a reversal of the orientation of cladia. Although a reversal is present in sample MNHN-IK-2015-545, the condition of the stem is little affected.

Distribution
South and SE Australia, Tasman Sea (Watson 2018), New Caledonia (present study).

Nominal species
Brief description, with emphasis on the distinctive features, and geographical distribution Cladocarpus elongatus Bedot, 1921 Colonies rather tall (up to 15 cm high), occasionally branched, fascicled; stem internodes with one frontal and a pair of axillar nematothecae, flanking the cladial apophyses, mamelon absent; cormidia with 7-8 intranodal septa, of which 2 are abaxial on proximal part; hydrothecae elongated, aperture slightly tilted forwards, margin with 11 rounded cusps, of which the median, abaxial one is the most developed; mesial nematotheca adnate for a very short portion of the basal abaxial wall of hydrotheca, laterals not overtopping the hydrothecal aperture; internal septum oblique rather than decidedly sigmoid, insertions on lateral walls of hydrotheca at different levels; phylactocarp borne on first cormidium, pinnate, branchlets with successive pairs of opposite to subopposite nematothecae; gonothecae ovoid, borne on apophyses of branchlets, male with apical, rounded, operculate aperture inclined to one side, female bigger, with broad, ovoid, lateral, subterminal aperture. Distribution: off the Atlantic coast of Morocco (Bedot 1921;Ramil et al. 1998).
Carpocladus fertilis Vervoort & Watson, 2003 Colonies rather tall (ca 12 cm high), with unbranched, fascicled stems; internodes with 1 frontal and a fronto-axillar nematotheca, apophyses alternate, without mamelons; cormidia with ca 7 intranodal septa, of which 3 are abaxial, below the hydrotheca, the remaining 4 on adaxial side of the hydrotheca; abaxial wall with median carina, forming a conspicuous dagger-shaped projection on front of median marginal cusp; aperture slightly tilted forwards, rim with 4 pairs of lateral cusps; a strong adaxial ledge projecting into hydrothecal lumen, prolonged upwards sigmoidally on lateral walls; mesial nematotheca covering basal third of abaxial hydrothecal wall, laterals just over-reaching margin; phylactocarps borne on first cormidia, each internode with a gonotheca and a forked costa comprising a hydrotheca. Distribution: Tasman Sea (Vervoort & Watson 2003).

Remarks
The relationships between several related aglaopheniid genera, viz. Cladocarpus Allman, 1874, Aglaophenopsis Fewkes, 1881, Streptocaulus Allman, 1883and Nematophorus Broch, 1918, have been discussed and interpreted by a number of authors (e.g., Ramil & Vervoort 1992a;Ansín Agís et al. 2001;Altuna et al. 2013) on the account of morphological characters alone. To these should be added other genera, such as Carpocladus Vervoort & Watson, 2003, Cladocarpoides Bogle, 1984and Wanglaophenia Vervoort & Watson, 2003, that make the case even more complex and, taken globally, it becomes evident that only a genetic study can be expected to clarify their relationships objectively.
The present hydroid, as well as Cladocarpus partitus sp. nov. and C. pennatus sp. nov. (see below), have gonosomes that do not conform accurately to any diagnosis of the abovementioned genera, displaying only some of their characters, as well as additional, distinctive ones. For this reason, these three new species are provisionally accommodated in the genus Cladocarpus, the oldest available name, pending a future phylogenetic study based on molecular markers.
A few congeners have hydrothecae resembling those of C. asymmetricus sp. nov., notably with respect to their elongated appearance and the presence of two lateral, oblique, intrathecal ridges. Their distinctive features are summarized in Table 1.
The new species is also highly distinctive in that its gonothecae are provided with nematothecae, a situation unknown in any of the Cladocarpus-like species described so far. Moreover, these nematothecae have three different morphologies and are present at different positions on the gonotheca.

Remarks
For a description of this species, refer to Schuchert (2003), who documented gonocladia bearing incipient gonothecae only, while the mature ones are still to be described. According to the present material, the plate-like intrahydrothecal septum is pierced in its center by a large, rounded foramen. The passage of the hydranth takes place in front of the septum and its body passes between the two lateral, arched perisarcal ridges.

Diagnosis
Cladocarpus with lightly fascicled, unbranched stems, whose rather long internodes bear a frontal row of 2-3 nematothecae, a lateral apophysis with a basal mamelon, as well as an anterior axillar nematotheca. Cladia relatively spaced from one another. Cormidia elongated, with up to 8 internal septa, 2 abaxial up to 6 adaxial. Hydrotheca deep, mesial nematotheca short, rim with median abaxial cusp, nearly smooth elsewhere; an internal ridge projecting forwards and slightly upwards from the lower fourth of the adaxial wall of hydrotheca, as well as an arched, two-winged septum above, leaving a slit-like, median passage for the hydranth. Phylactocarp borne on stem internode by means of a short apophysis; segmented into moderately-long internodes, each with one frontal, triangular nematotheca; gonothecae on distalmost internodes; tubular, with a main, lateral, subterminal, slit-like aperture, and an inconspicuous, secondary gutter-shaped aperture above.

Description
Colony erect, feather shaped, delicate, ca 6.5 cm high, hydrorhiza not observed. Stem unbranched although, in the present specimen, the distal part had been partly broken off, but still remained attached, European Journal of Taxonomy 615: 1-47 (2020) and was consequently displaced laterally by a new, regenerative colony tip that has grown up vertically, giving the impression that the old apex is merely a lateral branch; stem fascicled proximally, grading to monosiphonic distally; every additional auxiliary tube adhering to the dorsal side of the preceding one, not forming a beam around the main tube, but resulting in a laterally-flattened structure (Fig. 7B); division into internodes indistinct, except for 3-4 oblique, deeply-cut nodes towards the proximal part of hydrocaulus, passing through all cauline tubes at a time. Equivalents of internodes 700-1050 µm long, 200-225 µm wide, composed of 2-3 frontal nematothecae in a row, a short lateral cladial apophysis, a reduced nematotheca (with small, rounded aperture) on an inconspicuous mamelon at its base, as well as an axillar, anterior nematotheca rather lateral to it; there is no dorsal axillar nematotheca. Stem nematothecae large, inverted-triangular, with thick perisarc, apertures distal, wide, with inwardly- Portions from proximal (A, seen frontally; B, seen laterally) and distal (C, with insertion of phylactocarp) parts of stem. Hydrotheca seen laterally (D) and frontally (E), and details of its basal (F) and distal (G) parts; mesial nematotheca (H) seen frontally (left) and apically (right); internal septa in an apical view of the hydrotheca (I). Distal end of phylactocarp with two gonothecae (J). Scale bars: A-C = 500 µm; D-G, J = 200 µm; H, I = 100 µm. Taxonomy 615: 1-47 (2020) rolled abaxial wall, giving the impression that two circular apertures are present laterally; apophyses slightly shifted onto the anterior side of the colony, the two rows of hydrocladia forming an obtuse angle. Cladia relatively spaced from one another, up to 1 cm long, unbranched, divided into up to 12 cormidia by means of transverse, though not clearly demarcated nodes (75-95 µm wide), each internode 775-865 µm long, accommodating a hydrotheca and its 3 associated nematothecae: one mesial and a pair of laterals; up to 8 intranodal projections of the perisarc, of which 2 are given off from the abaxial side below the hydrothecal base, and up to 6 arise from the dorsal wall of the hydrotheca and project for a short distance into the lumen of the internode. Hydrotheca elongated, 600-635 µm deep, laterallyflattened, ad-and abaxial walls with slight basal bulges; a septum projecting slightly upwards from the lower portion of the adaxial wall reaches up to the middle of the thecal lumen, and is provided anteriorly with a distal swelling scattered with granular projections; a second, lamellar, two-winged septum is given off upwardly from the lateral sides of the hydrotheca at a rather acute angle, then changes its orientation and slightly plunges downwards, attaching its anterior border to the abaxial wall of the theca, leaving a slit-like, median passage between its two lateral 'wings'; hydrothecal aperture 225-230 µm wide, rim with a prominent, central, well-developed, abaxial cusp, nearly smooth elsewhere. Mesial nematothecae elongated, rather broad in frontal view, adnate for most of their length, leaving a short (40-50 µm) portion free from the base of the corresponding hydrotheca; aperture broad, abaxial wall inwardly-rolled, rim crenelate at corners; mesial nematotheca of first cormidium short, guttershaped and not coalescent with the hydrothecal base. Lateral nematothecae 145-155 µm long, broadly cylindrical, reaching the level of the hydrothecal rim; adaxial wall deeply scooped out, abaxial wall crenelate to wavy. Phylactocarp mounted on a short stem apophysis arising laterally, next to a cladial apophysis, on opposite side; divided into several moderately-long (360-485 µm) internodes by means of transverse to slightly oblique nodes, each bearing a frontal nematotheca similar to those of stem, with large apical apertures and inwardly-rolled abaxial walls, giving the impression that the nematothecae are bifid; last couple of internodes additionally provided with a basally concrescent gonotheca; the latter long, tubular (ca 1630 × 400 µm), tapering below, distally with a main, broad, subterminal, slit-like aperture with flimsy, wavy rim, above which a second, short, slender, gutter-shaped aperture is to be found. Sex undeterminable.

Remarks
Although not comprehensively described and/or illustrated, especially upon an apical examination of the hydrothecae, the internal septa of Cladocarpus bicuspis (G.O. Sars, 1874) possibly share morphological affinities with those of the present species. Indeed, a transverse septum, originating from the lateroabaxial hydrothecal walls, projects nearly horizontally midway into the lumen, then plunges down so as to meet the distal, swollen border of the adaxial hydrothecal ridge (G.O. Sars 1874: pl. 2 fig. 9;Kramp 1935: fig. 71b;Cornelius 1995: fig. 47c). Frontal views of the hydrotheca illustrated in the literature (Broch 1918: fig. 48c;Schuchert 2001: fig. 114b) do not provide sufficient information on the global aspect of the abaxial projection. Besides this possible common feature, the hydrothecae of C. bicuspis are distinctive through the presence of a median, abaxial pair of marginal cusps, separated from a squared to V-shaped gap prolonged downwards, till the level of abaxial ridge, as a perisarcal thickening; additional features related to its gonosome allow a rapid separation from the present new species (Cornelius 1995).

Distribution
Known only from its type locality, off New Caledonia (present study).
GALEA H.R., Aglaopheniid hydroids from off New Caledonia Cladocarpus pennatus sp. nov. urn:lsid:zoobank.org:act:7E29B1BC-C12D-43BE-8D91-0BB238C6CDBA Figs 6C-E, 8-9; Table 2 Diagnosis Cladocarpus with large, fan-shaped colonies, with strongly fascicled stems and side branches. Nodes rather indistinct, internodes with a proximal, frontal nematotheca, a cladial apophysis with its coneshaped nematotheca, as well as a fronto-axillar nematotheca. Cladia close to one another, divided into short internodes; first internode short, with a nematotheca, but no hydrotheca; remainder of cladium with normal cormidia. Hydrothecae facing backwards with respect to the antero-posterior plane of the colony; sigmoid, variously bulging abaxially from their lower halves; mesial nematotheca conspicuous, half adnate, projecting obliquely forward and upward (shorter and strongly pointing laterally on first cormidium); hydrothecal aperture with a median, triangular cusp and 1-2 pairs of laterals, decreasing in size adaxially; an internal, adaxial septum plunging down into the hydrothecal lumen for half its width. Gonosome composed of gonothecae arising from the cladial apophyses and phylactocarps borne on the first cormidium of a cladium that has lost its proximalmost, nematothecate internode. Phylactocarps elongated, set with consecutive pairs of lateral nematothecae, an additional, median, distal row occasionally present. Gonothecae dimorphic, male tubular, with recurved distal end bearing large aperture flanked by two lobes, female comparatively smaller and fusiform.

Description
Colonies erect, fan-shaped, up to 11 cm high and 8.5 cm wide, arising from rhizoid stolon composed of numerous branching, anastomosing, contiguous fibers firmly anchoring the whole structure on its substrate. Stems strongly fascicled, branched irregularly with a tendency to alternate, main stem supported dorsally by beam of auxiliary tubes, each provided with a longitudinal row of deeply-immersed, saccate nematothecae, having only their distal parts, bearing the apertures, protruding from the perisarc. There are no proximal oblique nodes passing through the fascicled stem; main tube with indistinct division into internodes, except for the distalmost parts of a colony, where the perisarc is thinner, and where weak transverse node delimit very short internodes; the latter composed of a proximal, frontal nematotheca, a laterally-directed cladial apophysis with its reduced conical nematotheca (with small, rounded aperture), and a second, frontal (axillar) nematotheca rather lateral to the apophysis; stem nematothecae elongated, with gutter-shaped apertures, occasionally inverted-triangular, with wide distal apertures and backwardly-rolled abaxial walls. Apophyses alternate along the stem, well-developed, delimited from the corresponding cladium by a deeply-cut, very oblique node; cladia close to one another, up to 7 mm long, slightly convex, proximally pointing upwards and distally downwards, the two rows coplanar; first cladial internode very short, ahydrothecate, but provided with a frontal, gutter-shaped nematotheca, ending in oblique node, separating it from the remainder of cladium, the latter comprising a regular succession of short internodes delimited by means of transverse nodes (100-115 µm wide); each internode 350-365 µm long, with a hydrotheca and its 3 associated nematothecae: one mesial and a pair of laterals; through a torsion of the cladium at its insertion on the corresponding apophysis, all hydrothecae face backwards with respect to the antero-posterior plane of the colony. Hydrothecae 260-270 µm deep, S-shaped, with thick abaxial wall, with an internal septum given off from the lower ¼ of the cavity and projecting slightly downwards so as to reach about the middle of the thecal lumen, ending distally in a perisarc plug; aperture ca 160 µm wide, rim with a central, prominent, triangular, abaxial cusp, continued laterally with 1-2 additional cusps decreasing in size adaxially. Mesial nematotheca adnate for ¾ to ½ of its length to the hydrothecal base, free part 115-125 µm long, aperture adaxial and gutter-shaped over entire length of free part; lateral nematothecae long (ca 145 µm), tubular, pointing out-and upwards, adaxial wall deeply scooped out. First cladial hydrotheca with comparatively shorter mesial nematotheca, given off from below its base, and distinctly pointing towards the dorsal side of the colony. Gonosome composed of phylactocarps, each associated with one gonotheca; gonothecae given off from the cladial apophyses just above the conical nematotheca and lateral to the distalmost internodal stem nematotheca; phylactocarps given off from cladia modified proximally as follows: the proximalmost ahydrothecate internode carrying the single, frontal nematotheca is replaced by a complete cormidium delimited by very oblique nodes; its mesial nematotheca is comparatively shorter than the subsequent ones, is given off from below the hydrothecal base, and is distinctly shifted on to the dorsal side of the colony; the second cormidium, also complete, is delimited proximally by an oblique node and distally by the first transverse node of the cladium; its mesial nematotheca is more elongated than that of the first cormidium and surpasses, for a certain distance, the hydrothecal base, but is still slightly shifted laterally; the third and subsequent cormidia are similar to those of a normal hydrocladium, with well-defined, straight mesial nematothecae. The phylactocarps are given off from the first cormidium, lateral to and above the mesial nematotheca, towards the front of the colony, by means of a short, conical apophysis delimited distally by transverse node, and having a long, guttershaped nematotheca at its base; phylactocarp composed of a double row of nematothecae, 6-10 in female colonies and up to 30 in males; in the latter, the double row is often supplemented distally GALEA H.R., Aglaopheniid hydroids from off New Caledonia

Remarks
Several Cladocarpus-like hydroids possess S-shaped hydrothecae provided with an adaxial septum, similar to those of C. pennatus sp. nov. However, there are morphological features enabling their specific separation, and these are summarized in Table 2.

Distribution
Known only from off New Caledonia (present study).

Remarks
For a description of this species, refer to Vervoort (1966) and Rees & Vervoort (1987); a quite recent synonymy is given in Vervoort & Watson (2003). In these accounts, only slightly bent hydrothecae, whose nematothecae have single apical apertures, were documented, not reaching the extreme degree of curvature ( Bifid mesial nematothecae were observed so far in specimens from Japan studied by Schuchert (2015).
In all samples examined the branching pattern is 'trifid', with either mono-(the 16 cm-high colony from sample MNHN-IK-2015-517) or lightly polysiphonic (all remaining material) stems; in addition, their hydrothecae are free from their corresponding internodes for ca ⅓ of their adaxial length, fitting the original account by Jäderholm (1903).
There is no thorough description available of the mode of branching in this species, especially at microscopic level. The original account is quite evasive ("Die Verästelung ist sehr regelmässig und characteristisch. Die nach allen Seiten gerichteten Äste sitzen fast immer zu zweien zusammen, sind sehr deutlich spiralförmig angeordnet und nach aussen gebogen" [The branching is very regular and characteristic. The branches are directed to all sides, almost always they are given off in pairs, are arranged in an obvious spiral, and are bent outwards]). However, Jäderholm (1903: pl. 14 fig. 5) provides a comprehensive illustration of the macroscopic appearance of a typical colony. According to his figure, a pair of plumes is given off at each geniculation of the stem, the successive pairs facing outwards with respect to the spiral built up by the stem.
Subsequent accounts seem to provide rather divergent data. Indeed, the material studied by Stechow (1909: 103, fig. 8) was devoid of the characteristic spiral growth pattern, the main stem giving rise, here and there, to secondary branches that further divide trichotomously. The colony studied by Billard (1918: 25, as Halicornaria sibogae) formed a helicoid sympodium ("Colonie […] ramifiée en sympode hélicoïde"), thus partly agreeing with the type, although nothing is said about its branching pattern. The account given by Vervoort (1966: 165) ("The structure of the colony is sympodially [sic]: the main axis is formed by the basal parts of successive plumes, arranged in spiral fashion, each succeeding plume rising about 8 mm from the base of the preceding plume") does not conform with the structure of the type either since, at each geniculation, only one plume, instead of two, is given off. Rees & Vervoort (1987) observed a "Sympodially built stem with helically arranged, unbranched plumes …" in their material, resembling those examined earlier by Vervoort (1966).
On the other hand, the colony illustrated by Rho & Park (1980: pl. 9 fig. 1) is undoubtedly similar to that of the type, despite their description (Rho & Park 1980: 27) providing only limited details: "Colonies large, not fascicled, spirally branched. The hydrocaulus [is] divided into regular internodes, zigzagshaped".
Finally, Vervoort & Watson (2003: 289) claim that they "have little to add to the descriptions of this characteristic species given by previous authors".
As noted above, the branching pattern met with in the present material from New Caledonia is superficially trifid, as follows: the stem is geniculate and describes a spiral; at more or less regular intervals, the main tube bifurcates at each geniculation: in the exact continuation of the long axis of the original portion before the geniculation, it is prolonged as a plume (bearing hydrocladia), while the divergent part continues, slightly inclined (with respect to the preceding longitudinal axis), as the main stem proper; from the base of the divergent portion of the stem, two (originally twin) tubes are given off: one runs downwards along the preceding portion of the stem below the geniculation (bringing polysiphony to the colony), while the other is given away upwards, forming a second plume (bearing hydrocladia) (Fig. 10A).
In this context, the specific separation between G. expansum and its closest congener, Gymnangium tubulifer (Bale, 1914), seems to rely exclusively on the appearance of the colonies resulting from their mode of branching. When describing his species, Bale (1914) referred to the structure of the colony of European Journal of Taxonomy 615: 1-47 (2020) G. vegae (Jäderholm, 1903), as did Vervoort & Watson (2003), who stated that the stem of G. tubulifer "… is geniculate and more or less spiral, composed of the proximal parts of stem elements that at each geniculation turn aside to form a branch. At the same place the proximal element splits off to form 3 ramifications of which [one] continues as the "stem", [one] as a branch pointing away from the original element, and [one] as a downwardly directed tube, covering the more proximal parts of the "stem"". This results in a colony whose distinctive appearance is depicted by Jäderholm (1903: pl. 15 fig. 1). In a molecular study by Ronowicz et al. (2017), G. expansum is shown to cluster with members of the genus Gymnangium Hincks, 1874 instead of with Taxella Allman, 1874, in spite of the colony structure showing obvious affinities with the latter. As noted by these authors, Stechow (1921) proposed a new genus, Halicetta, to accommodate G. expansum, with the following diagnosis: "hydrothecae elongated, curved but not bent, with no abaxial septum". This, however, does not differ much from characters of Taxella, even though emphasis was placed on characters of the gonosome in particular. A more comprehensive analysis is necessary to elucidate the generic affinities of Jäderholm's (1903) hydroid.

Distribution
Scattered records from the tropical and subtropical Indian and Pacific Oceans, from Zanzibar to Japan (Vervoort & Watson 2003

Remarks
For a recent description of this well-known species, refer to Di Camillo et al. (2011), who also provided an extensive synonymy.

Distribution
Widespread in tropical parts of the Indian Ocean, from Africa to Indonesia, and the northeastern South Pacific (Di Camillo et al. 2001).

Diagnosis
Lytocarpia with moderately tall, delicate colonies, with lightly fascicled, unbranched stems, divided into rather long internodes, each comprising 2-3 frontal nematothecae in a row, a lateral apophysis supporting a cladium with its conical nematotheca, and a couple of axillar nematothecae flanking the apophysis on each side of the stem. Cladia fairly close to one another, cormidia moderately long, with 6 intranodal septa, hydrotheca occupying distal ¾. Hydrotheca distinctly S-shaped, swollen basally, mesial nematotheca adnate for most of its length, free part projecting nearly upwards, and provided with large aperture behind an inwardly-rolled abaxial wall; lateral nematothecae tubular, with adaxially scooped walls, overtopping hydrothecal aperture. Rim with rounded-triangular median cusp, edges with two low, triangular cusps prolonged adaxially by a mere undulation. Gonosome an open corbula, distally on cladia, each internode with a costa and an axillar nematotheca; costae with a basal hydrotheca and a short appendage comprising 3-4 pairs of laterally-placed nematothecae; gonothecae lenticular.

Etymology
From the Latin 'frăgĭlis', meaning 'frail', with reference to the delicate appearance of its colonies.

Description
Colony erect, of a delicate appearance, comprising a single plume, originally taller than the 7.5 cmhigh fragment left after the breakage and subsequent loss of its distal part; arising from a rhizoid stolon firmly attached to hard substrate. Stem unbranched, lightly fascicled, grading to monosiphonic distally; GALEA H.R., Aglaopheniid hydroids from off New Caledonia main tube composed of a long (3.5 cm) proximal part devoid of hydrocladia but bearing large, saccate nematothecae in a single, frontal row, and a shorter part bearing cladia; both parts are separated by a short intervening prosegment with one frontal nematotheca, delimited at both ends by very oblique, deeply-cut nodes. Upper part divided, sporadically, into long segments by means of a few oblique nodes; segments further divided into regular, moderately long (680-840 µm) internodes delimited by transverse nodes (150-170 µm wide), inconspicuous wherever the perisarc is thick, but becoming obvious in youngest parts; each internode with 2-3 frontal nematothecae in a single row, a short cladial apophysis with its basal, simple nematotheca mounted on an inconspicuous mamelon, a nematotheca lateral to the apophysis (axillar, in front of stem), as well as an axillar nematotheca on dorsal side of the stem. Frontal nematothecae large, saccate, with wide aperture behind, sometimes giving the impression that one or two lateral apertures are present, due to their inwardly-rolled abaxial walls. Cladia alternate, fairly close to one another on each row, up to 1.3 cm long, composed of up to 18 cormidia. The latter moderately long (705-715 µm long, 65-70 µm wide at node), accommodating a hydrotheca in their distal ¾, and its 3 associated nematothecae: one mesial and a pair of laterals; 6 intranodal projections of the perisarc: 4 given off from the adaxial wall of the hydrotheca, while the remaining 2 from the abaxial perisarc of the internode. Hydrotheca 475-485 µm deep, S-shaped in lateral view, lower half distinctly swollen when seen frontally; mesial nematotheca adnate for most of its length, leaving a short, free, bifid portion reaching the middle of the theca; aperture wide, abaxial wall inwardly-rolled; lateral nematothecae conical, with gutter-shaped apertures in their adaxial wall; hydrothecal aperture 230-240 µm wide, rim with a prominent, rounded, abaxial cusp, lateral edges with two pairs of low, triangular cusps, prolonged adaxially by a mere undulation of the margin. Gonosome an open corbula on the modified distal portion of a cladium, after a sequence of 3-6 normal cormidia proximally; rachis divided into short internodes by means of transverse nodes; each internode with a costa (there is no distinct apophysis supporting it; costae alternate) and a large, saccate nematotheca (with gutter-shaped aperture) lateral to it; unlike the subsequent ones, the first internode of the corbula possesses an axillar nematotheca at junction between the insertion of costa and the internode; costae composed of a modified hydrotheca that retains its lateral nematothecae at their normal place, while the mesial one (with single, gutter-shaped aperture in this case) is placed a certain distance below the hydrothecal base, so as to allow the formation of a rib composed of about 3-4 pairs of nematothecae arranged along its length; except for hydrothecae of the 1 st or 2 nd rib, those placed more distally in the corbula possess an extra, gutter-shaped nematotheca on their dorsal side (compare Fig. 11J and 11K). The gonothecae, lenticular in shape, are inserted at the bases of costae, close to the large internodal nematotheca; perisarc flimsy.

Remarks
The hydrothecae of L. fragilis sp. nov. are mainly characterized by the notable bulging (both abaxially and laterally) of their lower halves, recalling the thecae of L. brevirostris (Busk, 1852) and L. tridentata (Versluys, 1899). The former is equally present in the material dealt with herein ( Fig. 11A) and is readily distinguished from the new species through its hydrothecae occupying the entire length of the cormidium, the lack of lateral swelling in their lower half, a mesial nematotheca provided with a single, gutter-shaped aperture as well as a hydrothecal rim bearing three pairs of large, triangular cusps, in addition to the median, abaxial one. Hydrothecae of L. tridentata share the same distinctive characters as those listed in L. brevirostris, but their rim is set with a pair of low, broad, triangular, lateral cusps, in addition to the median one (Migotto 1996).
As noted above in the description, the mesial nematotheca of L. fragilis sp. nov. has a wide apical aperture, partly camouflaged by a backwardly-rolled abaxial wall (Fig. 11I) that creates laterally two circular passages, giving the impression -upon a frontal view of the hydrotheca -that the nematotheca is bifid (Fig. 11H). Nematothecae having a similar aperture have been described in L. bathyalis Ryland & Gibbons, 1991(original account, Ryland & Gibbons 1991 fig. 14d-e) but, in this species, the nematotheca is adnate to the entire length of the abaxial wall of the hydrotheca, leaving only a short portion free that surpasses the rim. Conversely, a true bifid mesial nematotheca is to be found in L. furcata (Vervoort, 1941) (original account Vervoort 1941).

Distribution
Known only from its type locality, off New Caledonia (present study).

Description
Colony erect, with lightly fascicled stem irregularly branched, up to the 4 th order, so as to form an arborescent structure. Stem and branches divided into short internodes by means of transverse nodes. Proximal portion of branches devoid of cladia, but with a frontally-placed nematotheca on each internode. Subsequent internodes bearing alternate cladia, each accommodating a short apophysis and 3 nematothecae: one proximal, below the apophysis, one lateral next to it (axillar), and one conical at the base of the apophysis. Nematothecae on proximal internodes of side branches, as well as the inferior and axillar ones, inverted-triangular in general outline, basally adnate and rounded, distally free and there with a broad aperture with inwardly-curved adaxial wall, giving the impression that two lateral apertures are present. Conical nematotheca fairly developed, with rounded, apical aperture. Cladia close to one another, divided into short cormidia by means of transverse nodes, each cormidium comprising a hydrotheca and its 3 associated nematothecae: one mesial and a pair of laterals. Two intranodal septa are present: one basal, prolonged on opposite side into the hydrothecal lumen as a transverse to slightly upwardly-directed intrathecal septum, and one distal, at base of the lateral nematothecae. Mesial nematotheca arched, long, tubular, adnate for ⅔ of its length, free part almost reaching the hydrothecal rim; a short, spout-like apical aperture, as well as an ovoid one near junction with abaxial hydrothecal wall. Lateral nematothecae rather short, merely surpassing the hydrothecal rim, with circular aperture apically, and large, ovoid foramen adaxially. Hydrothecal rim with 7 cusps: median, abaxial one with thickened perisarc forming a small triangular anterior projection, and 3 pairs of laterals. First cusp narrow and triangular, second (middle) cusp often split in middle, and third (posterior) wide and broadly rectangular. Terminal stolonization often present on tips of branches. Corbula open, up to 9 mm long, replacing normal cladium, composed proximally of a normal cormidium, followed by a short internode bearing a mesial nematotheca, and a succession of up to 70 internodes bearing alternate costae; nodes oblique. Costal internodes short, bearing an arched costa and 4 nematothecae: 3 on ventral (internal) side, and one dorsally (external). Ventral nematothecae: one at base of the costa, another one lateral to it (both elongated and with gutter-shaped apertures), as well as a short, conical nematotheca at the base of the insertion of costa. Dorsal nematotheca conical, with rounded apical aperture and a large, rounded, adaxial foramen. Gonothecae lenticular, with flimsy, transparent perisarc, borne on base of costa by means of short, indistinct pedicel. Gonophores not seen.

Remarks
As indicated by the specific name, living colonies of this species are characteristically dark colored, due to a black pigment found in the coenosarc. This, however, has been lost in the present alcohol-preserved specimen, but its morphological features match those described earlier (see synonymy).

Diagnosis
Lytocarpia forming robust, rigid, unbranched colonies with strongly fascicled stems. Division into internodes indistinct, but each module with a proximal, frontal nematotheca, a cladial apophysis with its conical nematotheca and a pseudophylactocarp, as well as a fronto-axillar nematotheca. Pseudophylactocarps composed of a long succession of internodes bearing a mesial and two lateral nematothecae. Cladia close to one another, composed of short internodes, each accommodating a strongly S-shaped hydrotheca and its 3 gutter-shaped nematothecae; mesial one half adnate, projecting obliquely upwards, overtopping hydrothecal rim; the latter with strong median triangular cusp and 3 lateral pairs of wider and lower cusps. Corbulae on modified cladia, after a sequence of two normal cormidia; rachis geniculate, repetitive units with a costa and a spout-like nematotheca lateral to it; each costa with a proximal nematotheca, a hydrotheca with a posterior nematotheca and a downwardlydisplaced mesial nematotheca, so as to give rise to a sequence of internodes, each with a complement of 3 nematothecae. Gonothecae lenticular, flimsy, inserted at the base of costae.

Etymology
From the Latin 'pĭlōsus, -a, -um', meaning 'hairy', with reference to the hirsute aspect of its colonies, due to the profuse occurrence of pseudophylactocarps.

Description
Colony erect, of strongly-built appearance, comprising a single plume arising from a well-developed, much branched hydrorhizal mass. Stem unbranched, strongly fascicled, proximal part (2.5 cm long) devoid of hydrocladia, and provided with two deeply-incised, oblique nodes passing through all (main and accessory) tubes at a time. Main tube with thick perisarc, without evident division into internodes, but comprising a regular succession of modules composed of a proximal, frontal nematotheca, a lateral apophysis supporting a cladium, bearing a conical nematotheca (with small, rounded, apical aperture) near its base, as well as a fronto-axillar nematotheca; stem nematothecae large, saccate, adnate for more than half their length, adaxial wall strongly emarginated. Exceedingly long and lax pseudophylactocarps are regularly given off from the cladial apophyses, projecting onto the side opposite to corresponding cladium, freely rippling with the water currents; pseudophylactocarps composed of a succession of elongated (390-405 µm long) internodes comprising triplets of nematothecae, one proximal and mesial in position, and two other distal and laterally-displaced; proximalmost internode comparatively shorter, retaining only its mesial nematotheca. Cladia close to one another, arched backwards, up to 1.8 cm long, divided into relatively short (385-435 µm) internodes by means of transverse nodes, each internode accommodating a hydrotheca with its three associated nematothecae (all gutter-shaped): one mesial and a pair of laterals. Hydrotheca strongly S-shaped, with an internal septum given off from the proximal portion of its adaxial wall, the end of which reaches almost the middle of the lumen; mesial nematotheca about half adnate, projecting out-and upwards, and overtopping the hydrothecal margin; aperture 180-185 µm wide, rim provided with a prominent, rounded, central, abaxial cusp, followed laterally by 3 pairs of low, wide, rather inconspicuous, triangular cusps; lateral nematothecae almost tubular, strongly projecting forwards and slightly upwards. Corbulae on highly modified hydrocladia, arising after a couple of normal cormidia; corbula up to 17 mm long, open, tubular, rachis decidedly geniculate, not divided into distinct internodes; each equivalent of internode with a costa and a spout-shaped nematotheca lateral European Journal of Taxonomy 615: 1-47 (2020) to it; up to 34 costae per side of gonotheca; costa composed of a proximal, short, tubular part provided with a nematotheca, followed by a hydrotheca whose mesial nematotheca was displaced far below its base, so as to accommodate the insertion of a succession of highly modified hydrothecae not retaining their cavities, but represented only by their respective nematothecae; basal hydrotheca provided with an additional, posterior nematotheca; first modified hydrotheca in the row comparatively longer than the GALEA H.R., Aglaopheniid hydroids from off New Caledonia subsequent ones, and provided with two mesial nematothecae; all nematothecae on costa spout-shaped. Gonothecae lenticular, with flimsy perisarc, insert near the base of each costa.

Remarks
Hydrothecae of L. pilosa sp. nov. are morphologically similar to those of L. brevirostris (Busk, 1852) and L. tridentata with respect to their sigmoid shape in lateral view. However, in none of these the hydrothecae are produced abaxially (in their lower halves) to a similar extent, and their apertures are less tilted frontally. In addition, the new species is a much more robust hydroid, with a thick and strongly fascicled stem, with longer and densely-set cladia, and with profuse, defensive structures, the pseudophylactocarps.

Distribution
Known only from the type locality, off New Caledonia (present study).

Diagnosis
Species of Lytocarpia with tall, slender, pinnate colonies of delicate appearance. Stems unbranched, slightly fascicled, with long internodes provided with a frontal row of 4-10 nematothecae, a lateral apophysis supporting a cladium and its conical nematotheca, as well as with a fronto-axillar nematotheca. Cladia fairly distant from one another, shifted on to the anterior side of the colony. Cormidia short, with up to 7 intranodal ridges; hydrothecae strongly S-shaped, with ad-and abaxial ridges projecting far into their lumina; mesial nematotheca adnate for ¾ its length, free part projecting upwards, not reaching hydrothecal margin; the latter with strong, median, abaxial cusps and edges with 3 pairs of additional cusps, the 2 nd being comparatively more developed. Corbula on distal end of a hydrocladium, after a sequence of 5-18 normal cormidia; rachis geniculate, segments with a costal apophysis and a nematotheca lateral to it; costae forked, with a hydrotheca (devoid of its lateral nematothecae) in middle and appendages with successive pairs of opposite to subopposite nematothecae; gonothecae lenticular, flimsy, arising from the base of costal apophyses.

Description
Undamaged colonies reaching more than 14 cm high; erect, slender and of delicate appearance, unable to support themselves when out of liquid, though perisarc rather thick throughout the colony; hydrorhiza not seen; stems lightly fascicled, composed of several superimposed auxiliary tubes, each adhering to the dorsal side of the preceding one, not forming a beam around the main tube, but rather resulting in a laterally-flattened structure; a notable deeply-cut, oblique node some distance above the origin from hydrorhiza, passing through all cauline tubes at a time; occasional oblique nodes sporadically along the remainder of stem; division into additional internodes not always distinct, though transverse nodes (170-180 µm wide) are more noticeable in the younger parts of the stem, where the perisarc is thinner; each internode 2-4 mm long, comprising a frontal row of 4-10 saccate nematothecae (with gutter-shaped, adaxial apertures), a short (ca 60 µm) cladial apophysis above carrying basally a conical nematotheca (with small, rounded, apical aperture), as well as an elbow nematotheca (also with guttershaped aperture) lateral to the insertion of apophysis on the internode (fronto-axillar). Basalmost cladia broken off, but arrangement alternate along the longest portion of the stem; up to 3.7 cm long, the two rows shifted on to the anterior side of the colony so as to form an acute angle; cladia fairly distant from one another in each row; divided into rather short (585-600 µm) internodes by means of transverse nodes (145-150 µm wide), each comprising a hydrotheca and its three associated nematothecae: one mesial and a pair of laterals; hydrotheca 525-540 µm deep, strongly S-shaped, with 2 internal septa, one adaxial arising a short distance above the base, and one abaxial given off a certain distance below the aperture from the abaxial wall, both septa protruding at least into the middle of the hydrothecal lumen; internodes with a number of incomplete internal septa: 2 abaxial and up to 5 on their adaxial side; mesial nematotheca long, tubular, adnate for more than ¾ its length, leaving only a short (100-115 µm) portion free, provided with a gutter-shaped aperture along its whole free length; lateral nematothecae tubular, 215-220 µm long, aperture with rim deeply-scooped adaxially; hydrothecal margin with a prominent, rounded, abaxial cusp, continued on each side by three broad, triangular cusps, the second being the most developed. Gonosome an open corbula borne on a hydrocladium after a sequence of 5-18 normal cormidia; rachis slightly geniculate, divided into very short internodes (by means of transverse nodes), each bearing a costal apophysis and an elbow nematotheca lateral to it; costa separated from apophysis by transverse node; costa forked, with a basal hydrotheca (lateral nematothecae lost) in middle; mesial nematotheca situated far below the hydrothecal base, so as to accommodate the insertion of the 'anterior' arm, comprising 5-6 pairs of opposite to subopposite nematothecae; a nematotheca on the back of the hydrotheca, above which is inserted the 'posterior' arm, comprising 7-8 opposite to subopposite nematothecae; proximalmost costa of a corbula with the mesial nematotheca immediately below the hydrothecal base, not giving rise to the "anterior" arm set with nematothecae; all nematothecae elongated, with deeply-scooped adaxial margins. Gonothecae lenticular, with flimsy perisarc, arising from the base of the costal apophyses.

Remarks
None of the nominal species of Lytocarpia described so far (Schuchert 2019) possesses simultaneously two (ab-and adaxial) strongly-developed internal septa, creating such a distinctive, S-shaped appearance of their hydrothecae, as L. pseudoctenata sp. nov.
The new species shows striking resemblances with Aglaophenia ctenata (Totton, 1930) with respect to the morphology of both hydrothecae and some components of the gonosome. Indeed, hydrothecae of both are borne on short internodes, are strongly S-shaped and possess two intrathecal ridges, one GALEA H.R., Aglaopheniid hydroids from off New Caledonia abaxial, the other adaxial, projecting halfway across their lumina (compare Fig. 15B with Totton (1930: fig. 69a)). However, the hydrothecal apertures of A. ctenata appear more tilted forward (Totton 1930: fig. 69a;Ralph 1961: fig. 9b;Vervoort & Watson 2003: fig. 62e, g-i). Although both species possess similarly long cladia, those of A. ctenata are 'tightly packed' (compare image 'a' from the frontispiece of Vervoort & Watson (2003) with Fig. 12G herein). Its stem internodes possess "one terminal apophysis with a pair of opposite nematothecae at their base and one or two nematothecae on the proximal part European Journal of Taxonomy 615: 1-47 (2020) […]. No mamelon has been observed […]" (Vervoort & Watson 2003). As with the gonohydrocladium of L. pseudoctenata sp. nov., that of A. ctenata also appears bifid (Vervoort & Watson 2003: fig. 62j), but there is no hydrotheca associated with it, and the number and position of the nematothecae are also slightly different.

Distribution
Known only from off New Caledonia (present study).

Remarks
The present material agrees well with descriptions of Lytocarpia spiralis (Totton, 1930) by Ralph (1961) and Vervoort & Watson (2003) but, since it is devoid of its gonosome and the condition of the hydrothecal rim could not be assessed properly, it is assigned with a query to it.

Distribution
Previously known from waters around New Zealand (Vervoort & Watson 2003); New Caledonia (present study).

Diagnosis
Species of Lytocarpia with tall, exceedingly slender, pinnate colonies of a very delicate appearance, with lightly fascicled, unbranched stems. Division into internodes indistinct; a row of 8-17 frontal nematothecae between two successive cladial apophyses, the latter with a basal, simple, conical nematotheca, and a fronto-axillar nematotheca. Cladia widely-spaced from one another; cormidia quite long, with up to 11 intranodal septa, accommodating an elongate hydrotheca and its 3 associated nematothecae; free part of mesial nematotheca gutter shaped, borne on a prominent, basal, abaxial bulge of the hydrotheca; an adaxial, intrathecal septum projecting slightly upwards and over halfway into the hydrothecal lumen; rim with prominent, median, abaxial cusps, edges wavy. Corbula on distal end of cladium; rachis indistinctly divided; each segment with a lateral costa and a nematotheca near to its insertion point; costae with a hydrotheca with its full complement of nematothecae, as well as an additional one on dorsal side of internode; mesial nematotheca far below hydrothecal base, so as to give rise to an appendage set with lateral nematothecae.

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

Description
Colony erect, unable to support itself outside liquid, exceedingly slender and delicate; arising from branched, rhizoid stolon anchoring it in sandy bottom. Stem unbranched, lightly fascicled proximally, monosiphonic for most of its length; a deeply-cut, oblique node a certain distance above its origin from hydrorhiza; below the node, a succession of large, saccate nematothecae in a row along the main tube; above the node, the stem bears widely-spaced (2.5-3 mm apart), alternate cladia, the latter borne on short (ca 70 µm) apophyses given off laterally and towards the 'front' of the colony, the two rows of cladia forming an acute angle; division into internodes (nodes transverse, 160-170 µm wide) inconspicuous on stem, but equivalents of internodes comprising a row of 8-17 frontal, saccate nematothecae, a lateral apophysis above them, a simple, conical nematotheca (with small, rounded, apical aperture) on the basal part of the apophysis, as well as fronto-axillar nematotheca, rather lateral to the apophysis, having the distal part shifted on to the opposite direction; all stem nematothecae, except that borne on the mamelon, with large, adaxial, gutter-shaped apertures. Cladia up to 1.8 cm long, composed of up to 21 cormidia, not distinctly demarcated by transverse nodes; each cormidium 810-860 µm long, 100-105 µm wide at node, with a hydrotheca placed some distance after its proximal node, and three associated nematothecae: one mesial and a pair of laterals; 10-11 internodal projections of the perisarc, all but two given off from the adaxial wall of the hydrotheca; hydrothecae exceedingly long (680-705 µm), slightly conical, with a basal abaxial bulge, on the top of which is mounted the free portion of the mesial nematotheca; the latter long, cylindrical, slightly concave in general outline, adnate for about ⅔ of its length, free part 120-130 µm long, with gutter-shaped aperture all the way down to the junction with the lower abaxial wall of hydrotheca, apical rim distinctly crenulated; lateral nematothecae moderately long (170-175 µm), broadly tubular, reaching the hydrothecal margin, aperture scooped out on adaxial side, abaxial rim distinctly crenulated; hydrothecal aperture 225-235 µm wide, rim with a prominent abaxial cusp with crenulated apex, ridges rather wavy, without distinct cusps; an internal septum is given off from the lower part of the adaxial wall of the theca and projects for ⅔ into the lumen. Gonosome an open corbula borne on distal ends of cladia, after a succession of 6-10 normal cormidia; corbula up to 8 mm long, tubular, with straight rachis, not distinctly divided into internodes; segments short, with an indistinct lateral apophysis bearing a costa and a saccate nematotheca (with gutter-shaped aperture) lateral to it; gonothecae lenticular, with flimsy perisarc, borne near the insertion of the costa on the rachis; costae up to 20-21 per side of the gonotheca, comprising a hydrotheca with a complete set of nematothecae, in addition to which there is an extra nematotheca on the dorsal side of the internode; mesial nematotheca far below the hydrothecal base, leaving room for the insertion of a long appendage carrying 7-11 variously arranged nematothecae on both sides. GALEA H.R., Aglaopheniid hydroids from off New Caledonia  Fig. 17. A-B. Lytocarpia cf. spiralis (Totton, 1930)

Distribution
Known only from off New Caledonia (present study).

Remarks
For a recent description of this well-known species, refer to Di Camillo et al. (2009), who also provide an extensive synonymy. Schuchert (2003) noted striking resemblances between the hydrothecae of Aglaophenia disjuncta Pictet, 1893, a hydroid with a so far unknown gonosome, and those of the present species, and questioned their possible conspecificity. A few well-preserved, fertile specimens, undoubtedly assignable to Pictet's species, occur in material from off Vanuatu gathered during the MUSORSTOM 8 Expedition. Their appearance (Fig. 16D) immediately distinguishes them from typical colonies of M. phoenicea (Fig. 16C), in being more delicate, with a less rigid and straw-colored perisarc, with more distant and comparatively longer cladia, with longer cormidia and slightly larger hydrothecae.
Stems of the species described by Pictet (1893) are lightly fascicled and scarcely branched, as for instance with one branch occurring in the tallest (6.5 cm high) specimen available. The stem and side branches are transversely divided into moderately long internodes, each bearing a cladial apophysis and 3 nematothecae, two large and one reduced: one at the base of the apophysis, a second axillar, and a short, conical theca on a mamelon (Fig. 18B). The large nematothecae are half adnate to the internode and possess a small, rounded aperture projecting laterally, as well as a large, broadly ovoid GALEA H.R., Aglaopheniid hydroids from off New Caledonia aperture behind. The proximal parts of the stem and branches are devoid of cladia, bear a row of large nematothecae with a conical distal half and have one of their apertures pointing upwards, while the other is comparatively larger and situated behind. The characteristic shape of the hydrothecae is depicted in Fig. 18C. The gonosome is typical of Macrorhynchia, and replaces a normal cladium, not forming pseudo-corbulae, but isolated phylactocarps; the proximalmost internode is a normal cormidium, on the distal part of which is inserted a long appendage with pinnate appearance resuting from the presence of (often) opposite pairs of exceedingly long nematothecae with two apertures: one small, apical, the other ovoid, at the base of the nematotheca. Occasionally, a few additional nematothecae in a row are to be found on the outer side of the phylactocarp. The gonothecae are large and lenticular, with flimsy perisarc, and are borne near the base of the appendage, amongst the proximalmost nematothecae.

Distribution
Widespread in the tropical parts of the Indian and southern Pacific oceans (Di Camillo et al. 2009).   Table 3 Diagnosis Species of Macrorhynchia with a distinctly spirally-twisted stem, giving rise at each bend to a side branch that branches soon again, forming a bifid ramification. Stem and side branches strongly fascicled.
Internodes short, with a proximal frontal nematotheca, a cladial apophysis above with its simple, conical nematotheca and a fronto-axillar nematotheca; cauline nematothecae saccate, with deeply scooped adaxial walls. Cladia alternate, fairly close to one another; cormidia moderately long, hydrotheca cupshaped, rather deep, aperture slightly sloping frontally, rim with 9 triangular cusps with rounded tips, of which the median, abaxial one is the most prominent; a slightly sigmoid, adaxial, intrathecal septum given off softly obliquely, reaching almost to abaxial wall; mesial nematotheca with short, spoutlike aperture, not reaching middle level of hydrotheca; lateral nematothecae barrel-shaped, with rim scooped out adaxially. Pseudophylactocarps, composed of chains of atrophied hydrothecae, borne on proximal parts of branches. Phylactocarp borne on a modified cladium, after 1-2 normal cormidia; first (occasionally second) segment, an atrophied hydrotheca, with its mesial nematotheca displaced more distally, and a short, lateral projection (on one side) bearing a couple of nematothecae similar to the laterals; gonotheca lenticular, flimsy, on top of atrophied hydrotheca, between the lateral nematothecae; gonophore, a medusoid.

Etymology
From the Latin 'spīra', meaning 'spiral', with reference to the distinctive shape of the stem.

Description
Colonies erect, sympodially built, with fascicled stems and side branches, grading to monosiphonic distally. Stem straight basally for a varied length, then bends at irregular intervals adopting a spiral arrangement. At each bend, a side branch arises as a rectilinear prolongation of the preceding portion of the stem, and usually ramifies once a short distance from its origin, both branches bearing hydrocladia for most of their length; proximally, a linear succession of saccate nematothecae with large apical foramina. Division into internodes indistinct wherever the perisarc is thick, but becomes evident towards the distal parts of the branches; internodes relatively short (400-420 µm long, 245-250 µm wide at node), with a large, proximal nematotheca, a cladial apophysis above, a fronto-axillar nematotheca, and a simple, conical nematotheca (with small, rounded, apical aperture) on the basal part of apophysis; nematothecae saccate, adnate for most of their length, having apically a large aperture whose rim is lowered adaxially. Cladia alternate, up to 14 mm long, composed of short cormidia (475-490 µm long, 95-100 µm wide at node), each accommodating a hydrotheca and its three nematothecae: one mesial and a pair of laterals. Hydrotheca cup-shaped, rather deep (390-400 µm), abaxial wall 215-240 µm long, straight for most of GALEA H.R., Aglaopheniid hydroids from off New Caledonia its length, gently expanding towards aperture; the latter 205-215 µm wide, slightly sloping frontally; rim with 9 rounded cusps, the uneven, abaxial one being the most prominent, and slightly inwardlycurved, the 4 pairs on the edges being comparatively broader and of varied development; an internal  (Nutting, 1900) Mesial nematotheca adnate for most of its length to the abaxial wall of hydrotheca, distal tip reaching the hydrothecal aperture. Gonosome described by Galea (2013). Distribution: tropical western Atlantic (Calder 1997). (Nutting, 1900) Mesial nematotheca adnate for most of its length to the abaxial wall of hydrotheca, distal tip reaching the hydrothecal aperture. Gonosome described by Ansín Agís et al. (2001). Distribution: tropical western Atlantic, Cape Verde Islands (Calder 2013).

M. mulderi
M. racemifera (Allman, 1883) Poorly known species, with mesial nematotheca adnate for most of its length to the abaxial wall of hydrotheca, distal tip overtopping the hydrothecal aperture. Gonosome described in the original account. Distribution: off Bahia, Brazil (Allman 1883). (Fewkes, 1881) Poorly known species, with mesial nematotheca adnate for most of its length to the abaxial wall of hydrotheca, distal tip overtopping the hydrothecal aperture. Distribution: tropical western Atlantic (Calder 1997). (Fewkes, 1881) Poorly known species, with mesial nematotheca adnate for almost the whole length of the abaxial wall of hydrotheca. Gonosome unknown. Distribution: Montserrat (Fewkes 1881). (Nutting, 1905) Poorly known species, with rather deep hydrothecae, with nearly horizontal aperture; rim with median, abaxial cusps and 3 pairs of laterals; mesial nematotheca becoming free in middle of hydrotheca, laterals tubular and narrow, distinctly overtopping the hydrothecal rim; phylactocarps with normal cormidium proximally, followed by a few short internodes carrying abortive (closed) hydrothecae that retain only their normal complement of nematothecae; no pseudophylactocarps. Distribution: Hawai'i (Nutting 1905). Table 3. Nominal species of Macrorhynchia Kirchenpauer, 1872 with saccate hydrothecae and adaxial but no abaxial, intrathecal septa, similar to those of Macrorhynchia spiralis sp. nov., and their morphological differences to the new species.

M. similis
GALEA H.R., Aglaopheniid hydroids from off New Caledonia septum, of a slightly sigmoid appearance, is given off softly obliquely from the lower part of the adaxial thecal wall, penetrating deep into the lumen, almost reaching the abaxial wall; mesial nematotheca fused to the abaxial wall of hydrotheca for most of its length, leaving distally a short (45-60 µm long), spout-shaped aperture, not reaching the middle of the hydrotheca; lateral nematothecae broadly barrelshaped, 110-120 µm long and ca 50 µm wide at aperture, rim scooped out on adaxial side. Fertile colonies produce two distinct structures: one not associated to the gonosome, the other being part of it. The former are pseudophylactocarps, composed of a chain of modified hydrothecae devoid of lumina, but retaining their complement of nematothecae (the latter are all tubular, with a rounded distal aperture and an ovoid, proximal, adaxial one); they are abundantly borne on small, alternate apophyses arising regularly and slightly laterally to the nematothecae of the proximal (acladiate) portion of branches, and encircle their long axis; no gonothecae have been observed associated with the pseudophylactocarps. The gonosome proper is borne on the distal parts of distally-modified cladia that retain proximally 1 (occasionally up to 4) normal cormidia, followed by 1-2 elongated internodes representing atrophied hydrothecae (devoid of lumina) that retain their normal complement of nematothecae, in addition to which a pair of nematothecae (similar to the laterals) is mounted on a conspicuous lateral, subterminal projection. There is some variation in the structure of the proximal part of the fertile cladium: the proximalmost hydrotheca (when only one is present) may be suppressed and replaced by one or two short internodes, the proximalmost bearing one nematotheca, the second three (one mesial and a pair of laterals). Gonothecae lenticular, 1150-1380 µm long and 750-795 µm wide, with flimsy perisarc, inserted between the pair of lateral nematothecae of the distalmost, atrophied hydrotheca; the gonophore is a medusoid, composed of a central spadix encircled by a single layer of large oocytes (the holotype is a female colony), and bearing apically a belt of refringent corpuscles.