Sinetectula gen. nov., a new genus of Pisaniidae (Gastropoda: Buccinoidea) from the tropical Indian and Pacific Oceans

The genus Sinetectula gen. nov. is proposed to accommodate Triton egregius Reeve, 1844, Buccinum cinis Reeve, 1846, Buccinum nigricostatum Reeve, 1846, Buccinum (Pollia) farinosum Gould, 1850, Pisania naevosa Martens, 1880, Pollia shepstonensis Tomlin, 1926 and one still undescribed species. These species are discussed and compared, and remarks on their biogeography are provided. The occasional appearance of a labral denticle is recorded and the morphological variability of the group is discussed. The radula of S. egregius gen. et comb. nov. is described.


Introduction
The buccinoidean family Pisaniidae Gray, 1857 comprises a diverse clade of at least 230 known living species, distributed throughout the tropic and warm-temperate marine zones. About 100 of them are found in the Indo-West Pacifi c. Although the last 20 years have witnessed the description of many genera and numerous species in the family, both living and fossil, some groups remain taxonomically homeless or have been placed in heterogeneous catch-all genera such as Engina Gray, 1839.
One particular group of pisaniids that has long been recognized as requiring its own genus is a complex of at least seven species centered on Triton egregius Reeve, 1844(Cernohorsky 1975. These species have either been assigned to Engina Gray, 1839 in the broad sense (Cernohorsky 1975: 190-191) or, in the case of Buccinum cinis Reeve, 1846, to Caducifer Dall, 1904(Keen 1958 or Monostiolum Dall, 1904(Keen 1971. These assignments have been widely seen as provisional (Cernohorsky 1975: 191;Watters & Finlay 1989: 48;Watters 2009: 266;Fraussen & Rosado 2011: 77), but no assignment has yet been proposed. The presence of phenotypic variation and overlap among the genera Engina, Monostolium and Caducifer has caused much confusion and nomenclatural instability when assigning species to these taxa. Therefore, we here propose and discuss the new genus Sinetectula gen. nov. to accommodate the aforementioned species, with the aim to provide a more stable generic classifi cation that can be used as a framework for future taxonomic and phylogenetic studies.

Material and methods
Empty shells of Pisaniidae, from the Cantharus group in particular, have been studied during visits to the collections of public institutes and those of private collectors. The present study is based on conchological morphology mainly, because molecular data are not yet available and shell characters are essential for the eventual recognition of fossil members. A specimen, with SEM photographs of its radula, was received from Yuri Kantor (IEE RAS).
Unless otherwise indicated, material from the French expeditions is deposited in the collections of the Muséum national d'histoire naturelle (MNHN), Paris, France. Apart from types, no individual catalogue numbers have been allocated, but lots are unambiguously designated and retrievable by the combination of expedition acronym and station number.
Bathymetric ranges are provided for each species, considering all the material and live-collected specimens only (when applicable), and are reported as the shallowest and deepest stations as explained by Bouchet et al. (2008).
The method of Verduin (1977) was employed to count the number of protoconch whorls.

Diagnosis
Shell small (maximum length to about 34 mm), sturdy, fusiform, basally constricted; whorls weakly convex, separated by appressed suture; sculpture cancellate, dense, consisting of narrow but high spiral cords and fi ne axial ribs, spiral cords covered with obscure axial lamellae, spiral interspaces with fi ne secondary spiral threads or traces of them; subsutural sinus present; outer-lip edge serrated, evenly convex in profi le, with fi ne lirae extending into aperture; parietal knob at the adapical end of the inner lip prominent, accentuating anal notch; columella with two adapical knobs; columellar callus expanded towards base and along siphonal canal, edge slightly fl aring, surface sculptured with tiny knobs; siphonal canal open, dorsally weakly recurved.

Etymology
Sinetectula gen. nov. is derived from the Latin 'sine', meaning 'without' in combination with 'tectula', meaning 'little roof', or, in other words, 'little homeless'. This also conjures up the contrast with the appearance of these small shelled gastropods that have, in reality, their home always with them. It also conjures up the contradiction that appears by virtue of the etymology by turning the 'little homeless' into 'not homeless', now that the name comes into existence. the parietal part of the columella, much broader and fewer spiral cords with much narrower interspaces, fewer and much broader axial ribs, and a straight or weakly convex (rather than convex) outer lip.
Species of Clivipollia Iredale, 1929 differ from Sinetectula gen. nov. in their larger protoconch consisting of 3½ to 3¾ whorls, the fewer but much more prominent and more rounded axial ribs, the absence of a parietal denticle at the adapical end of the inner lip with a weaker but usually much broader anal notch, the well-defi ned outer-lip denticles that sometimes extend as lirae into the aperture, the broad and deep notch between the anal denticle and the outer-lip denticles and the usually more vivid colour (Fraussen & Stahlschmidt 2016: 30-38).
The genus Engina differs from Sinetectula gen. nov. in its fewer but usually more prominent axial ribs, the usually stronger apertural sculpture with prominent knobs within the outer lip and radially orientated lirae on the columellar callus (instead of knobs). The radula of Engina turbinella Kiener, 1836, the type species of Engina (originally cited as Engina zonata Gray, 1839), looks similar to the radula of Sinetectula egregia gen. et comb. nov. but differs by the presence of 5 pronounced cusps on the rachidian tooth (Ponder 1972: 252, fi g. 1-10).
The American genus Parviphos Sarasua, 1984 differs from Sinetectula gen. nov. in its strongly varicate outer lip, fewer axial ribs, and the more prominent parietal tooth at the adapical end of the inner lip (Watters 2009: 265-270, fi gs 232-262).
The American genus Monostiolum differs from Sinetectula gen. nov. in its axial sculpture reduced or absent on the last whorl, the weak apertural sculpture, and the absence of lirae within the outer lip. The spiral sculpture tends to be much fi ner in Monostiolum, and the spire is typically much higher, making for a slenderer shell (Watters 2009: 259-265, fi gs 197-223).
The East African genus Micrologus Fraussen & Rosado, 2011 looks very similar in shape but differs from Sinetectula gen. nov. in its fi ner spiral sculpture with broader interspaces and a higher amount of secondary spiral cords (especially on the base and the transition to the siphonal canal), the much narrower columellar callus, the absence of knobs or lirae on the columellar callus and the absence of a serrated edge along the outer lip (Fraussen & Rosado 2011: 76-78, fi gs 1-6).
The West Pacifi c genus Cancellopollia Vermeij & Bouchet, 1998 looks similar but differs from Sinetectula gen. nov. in its smooth columellar callus, the stronger spiral sculpture without secondary spiral cords, the absence of a strong (bicarinate) subsutural cord and the stronger varix on the outer lip (Vermeij & Bouchet 1998: 479).
The genus Pisania Bivona, 1832 differs from Sinetectula gen. nov. in its much smoother, usually glossy shell wihout axial sculpture and the smoother aperture. The radula of Pisania striata (Gmelin, 1791), its type species (originally cited as Pisania striatula Bivona & Bernardi, 1832), looks similar to the radula of Sinetectula egregia gen. et comb. nov. but differs by the presence of 5 more pronounced cusps on the rachidian tooth, the slightly shorter outer cusp on the lateral teeth and the absence of a protrusion at the inner margin of its base (Cernohorsky 1971: 138, fi g. 17;Ponder 1972: 260, fi g. 1-1).
As with the variation in protoconch morphology, shape and sculpture also vary quite considerably among species of Sinetectula gen. nov. This is not unusual within Pisaniidae, or Buccinidae Rafi nesque, 1815 in the broad sense. Indeed, Sinetectula gen. nov. has a somewhat heterogenous appearance. The shape varies among the species, with an ovate shape of S. farinosa gen. et comb. nov., in contrast with the slender shape of S. egregia gen. et comb. nov. and others. The shape varies also within a single species, with slender and broad specimens occurring within, for example, S. cinis gen. et comb. nov. (according to their distribution, the broader ones from Galapagos, while the more slender ones usually from Costa Rica) and S. shepstonensis gen. et comb. nov. (the limited material we studied suggests a variation according to bathymetric distribution, if not latitudinal distribution: the slender ones from deeper water off Somalia, while the broad ones are from shallower water off Mozambique and South Africa). The convexity of the whorls is stable in all species except S. shepstonensis gen. et comb. nov., where the specimens with a broader shell have a more convex whorl compared to the slenderer specimens from deeper water. The sculpture is moderately constant within a single species. As a result, the differences between the species can be described in the strength of the spiral cords and the axial ribs as well as in their number.

Distribution
Sinetectula gen. nov. is known from the tropical Indo-West Pacifi c, from eastern Africa in the west to the American West Coast in the east. Yet, we have not detected any specimens or species from the Atlantic. Sinetectula gen. nov. joins the related genus Clivipollia in having representatives in both the Indo-West Pacifi c and tropical eastern Pacifi c. Shasky (1987: 30), and referred to by Skoglund (1992:  Sinetectula gen. nov. is so far not known from the fossil record. In the case of S. cinis gen. et comb. nov. and S. nigricostata gen. et comb. nov. it is likely that they, or their immediate ancestors, arrived in the eastern Pacifi c from the west no later than the Early Pleistocene (Vermeij 1987). (Reeve, 1844)

Remarks
Sinetectula egregia gen. et comb. nov. is recognisable by its characteristic colour pattern consisting of small dark brown spots situated in the space between the spiral cords where they cross the axial ribs. Occasionally, these spots are also present in the axial interspaces. These spots produce, when seen without magnifi cation and, depending on their arrangement, a combination of moderately broad spiral bands (1 on the spire whorls and 2 on the body whorl) or dark axial blotches. This in combination with a rather rough sculpture dominated by 2 strong primary spiral cords on the spire whorls, gives the spire whorls a rather angular appearance. The colour on the spiral cords (white or pale) and spiral interspaces (usually darker) may inverse after crossing the prelabral varix, where, nearing the edge of the aperture, the spiral cords may become darker while the interspaces become paler or white (see Fig. 2C).  The serrated edge of the outer lip deserves some closer study and is worth an extensive description. The protruding cusps are preceded by spiral interspaces while the notches are in the extension of the spiral cords. Specimens with an inversed pattern, as described in the previous paragraph, cause the optical illusion that the white spiral cords produce the white cusps (in reality it are the darker interspaces that lead the way to the white cusps).
The serrated edge shows quite some variation among the species as well as within some individuals. The spiral cords alternate between strong and slightly weaker: the original (primary) spiral cords already present on the upper spire whorls are slightly stronger than the (secondary) spiral cords that took shape along the antepenultimate whorl. As a consequence, the notch preceded by a stronger primary spiral cord is often slightly deeper than the notch preceded by a slightly weaker secondary spiral cord. This is more materialised along the basal (abapical) part of the lip (slightly above the transition from base to siphonal canal). As a result, the serrations may be arranged in pairs, causing a somewhat bilirate appearance.
The 12 th or 13 th cusp (counting from the suture) is often fl anked by deeper and slightly broader notches and, as a result, accentuated (see Fig. 1B, G). We haven't detected any specimen where this accentuated cusp is also more protruding and surpassing the other cusps.
The protoconch is paucispiral, consisting of 1¼ whorl with a rather fl attened shape (see Fig. 1D-E, O). The number of protoconch whorls is remarkably constant among all material we studied, with the exception of a single specimen from Sulawesi (KF 4854) that has 1¾ protoconch whorls (see Fig. 1L). This shell is identical to other shells, including the shape of its protoconch, apart from the fact that the last protoconch whorl continues turning another half whorl. We counted the number of spiral cords according to the method of Verduin (1977). Other methods, for example following the suture in between the protoconch whorls, may be responsible for the 2 protoconch whorls counted in Phos amoenus by Schwengel (1950: 81). The slightly eroded apex of dead-collected but otherwise fresh looking specimens (for example KF 2164 from Guam) may have the sculpture along the fi rst teleoconch whorl smoothened in such a subtle way that the protoconch appears larger and with more whorls.
In some specimens, the adapical apertural knob, inside the apertural lip, may be situated slightly more adapically than the parietal knob on the columella, resulting in a somewhat skewed anal notch, rather than having both anal knobs aligned.
For the description of the radula, we refer to the diagnosis under Sinetectula gen. nov. above.
Sinetectula naevosa gen. et comb. nov. differs from S. egregia gen. et comb. nov. by its larger protoconch (0.9 mm long and 0.9 mm in diameter (KF 5029) vs 0.6 to 0.7 mm long and 0.7 to 0.8 mm in diameter in S. egregia gen. et comb. nov.), the slightly higher number of protoconch whorls (1½ instead of usually 1¼), the upper spire whorls that are higher and increase in size more quickly, resulting in a slenderer spire (whereas in S. naevosa gen. et comb. nov. the transition from 3 rd to 4 th whorl falls within the fi rst 5 mm of the teleoconch length, in S. egregia gen. et comb. nov. this occurs from the 4 th to 5 th whorl that falls within these fi rst 5 mm). The spiral sculpture of S. naevosa gen. et comb. nov. is fi ner, starting with 3 fi ner primary spiral cords on the fi rst teleoconch whorls (instead of 2 dominant ones), resulting in a more convex shape of the upper spire whorls. The secondary spiral cords, to the contrary, are slightly stronger when situated in the center between the primary spiral interspaces in S. naevosa gen. et comb. nov. but lower in number (1 to 3 vs 4 or 5 in S. egregia gen. et comb. nov.). By contrast, the number of secondary spiral cords on the subsutural slope is higher in number in S. naevosa gen. et comb. nov. The axial ribs are weaker but slightly higher in number, especially on the spire whorls.
Sinetectula farinosa gen. et comb. nov. differs from S. egregia gen. et comb. nov. by its higher number of protoconch whorls, the much broader shape with shorter spire and slightly more convex whorls, the more cancellate sculpture with stronger spiral cords and axial ribs that are covered by pronounced incremental lamellae, sharper denticles on the columella and fewer (5 to 8) but stronger knobs inside the outer lip. (Reeve, 1846)

Distribution
Sinetectula cinis gen. et comb. nov. is restricted to the central eastern Pacifi c. We studied specimens from Costa Rica and Galápagos. López-Pérez (2013) recorded the species from Mexico. We have not studied the material from Mexico preserved in SBMNH or the material from Colombia preserved in UV.

Remarks
Sinetectula cinis gen. et comb. nov. merits special attention because of the presence of a distinct labral tooth. The tooth, fi rst noted by Vermeij (2001: 464, 475, 497), is the eighth (counting from the suture) of 13 outer-lip serrations (without counting along the siphonal canal) formed as an enlarged and protruding space between external spiral cords. A single specimen (KF 2123) has an additional weak tooth formed by the seventh outer-lip serration (see Fig. 3D).
Only Sinetectula nigricostata gen. et comb. nov. has, occasionally, a similar labral tooth, but no comparable labral tooth is found among members of such related genera as Bailya M. Smith, 1944, Caducifer, Clivipollia, Dianthiphos Watters, 2009, Jeannea Iredale, 1912, Monostiolum, Parabailya Watters & Finlay, 1989, Parviphos or Speccapollia Fraussen & Stahlschmidt, 2016 At a maximum length of 34.5 mm (Simon Aiken: pers. com. 2020), S. cinis gen. et comb. nov. is also the largest member of this genus. This exceptional size could be related to the high planktonic productivity of the waters around the Galápagos Islands. Other species of the genus are smaller and they usually live in reef environments where planktonic productivity tends to be low.
We follow Keen (1958Keen ( : 398, 1971 and consider Caducifer? thaleia to be a subjective junior synonym of S. cinis gen. et comb. nov. The type specimen (ANSP 81972), from Cocos Island, has a damaged outer lip and therefore does not show a labral tooth; but specimens from Cocos Island (SBMNH) with an intact outer lip do express a labral tooth. Specimens from Costa Rica are not obviously different from typical S. cinis gen. et comb. nov. from the Galápagos Islands, apart from the usually somewhat slenderer shape.
Sinetectula shepstonensis gen. et comb. nov., a species from eastern Africa with an almost identical sculpture, differs from S. cinis gen. et comb. nov. in its more equally sculptured outer lip without labral denticle, the slightly fi ner spiral sculpture with fi ne secondary spiral cords, the more convex whorls and the weakly constricted base resulting in a slightly narrower siphonal canal. Sinetectula nigricostata gen. et comb. nov. is the second member of the genus that has an apparent labral denticle. It differs from S. cinis gen. et comb. nov. in its convex whorls, the broader shape with a shorter spire, the fi ner spiral sculpture, the stronger axial ribs that are lower in number, the weak or absent incremental lamellae, the constricted base with longer siphonal canal, the pattern consisting of fi ne spiral lines and the smaller adult size.

Remarks
Sinetectula farinosa gen. et comb. nov. is recognisable by its broad, ovate shell in combination with a rather cancellate sculpture.
The furrowed edge of the labral lip is typical of the genus, very similar in shape to S. egregia, with a similar tendency to arrange the cusps in pairs, but the slightly deeper basal notches accentuate the basal cusp much less (see Fig. 4B, F).
The protoconch is multispiral, consisting of 2 to 2½ whorls, the last whorl with a tiny suprasutural spiral keel (see Fig. 4D).
Sinetectula egregia gen. et comb. nov. differs from S. farinosa gen. et comb. nov. by its lower number of protoconch whorls (1 vs 2 to 2½), the slender shape with a higher spire, the weaker sculpture with fi ner spiral cords and fi ner axial ribs, the weaker denticles on the columella and the higher number (usually 12) but weaker knobs inside the outer lip.

Type locality
Mauritius.

Distribution
Sinetectula naevosa gen. et comb. nov. is an overlooked species, the few records we found being under former combinations of S. egregia gen. et comb. nov. from along the eastern African coast. The species is known from Mauritius (type locality) and we could confi rm records from South Africa in the south and Somalia in the north. Further study may reveal a much wider range.

Remarks
We studied a limited number of specimens of Sinetectula naevosa gen. et comb. nov. and, therefore, we are not able to discuss the variability within the species. These shells conform to the original description, especially the characteristic number of spiral cords and axial ribs as well as the well-defi ned anal notch.
The shells differ from Sinetectula egregia gen. et comb. nov. by the larger protoconch (0.9 mm long and 0.9 mm in diameter (KF 5029) vs 0.6 to 0.7 mm long and 0.7 to 0.8 mm in diameter in S. egregia gen. et comb. nov.), in combination with a smaller teleoconch size, the slightly higher number of protoconch whorls (1½, instead of usually 1¼), the upper spire whorls that are higher and increase in size more quickly, resulting in a slenderer spire. Whereas in S. naevosa gen. et comb. nov. the transition from 3 rd to 4 th whorl falls within the fi rst 5 mm of the teleoconch length, in S. egregia gen. et comb. nov. it is the transition from 4 th to 5 th whorl that falls within these fi rst 5 mm. The spiral sculpture of S. naevosa gen. et comb. nov. is fi ner, starting with 3 fi ner primary spiral cords along the fi rst teleoconch whorls (instead of 2 dominant ones), resulting in a more convex shape of the upper spire whorls. The secondary spiral cords, to the contrary, are slightly stronger when situated in the center between the primary spiral interspaces in S. naevosa gen. et comb. nov. but lower in number (1 to 3 vs 4 or 5 in S. egregia gen. et comb. nov.). Also, the axial ribs in S. egregia gen. et comb. nov. are weaker and lower in number. The brown pattern of S. naevosa gen. et comb. nov. appears to be more evenly arranged along slightly narrower spiral bands than is the case in S. egregia gen. et comb. nov.  (Reeve, 1846) Fig. 7D). The labral denticle is usually situated at the 7 th (vs 8 th in S. cinis gen. et comb. nov.) spiral interspace. Depending on the strength of the secondary spiral cords, the fi rst interspace may be counted double in the case that it is divided by a secondary spiral cord that has become as strong as the primary spiral cords, thus with the labral denticle appearing in the 8 th interspace.

Sinetectula nigricostata
Sinetectula cinis gen. et comb. nov. differs from S. nigricostata gen. et comb. nov. in its laterally more fl attened spire (instead of convex whorls), the broader spiral cords, the weaker axial ribs that are higher in number, the stretched base (instead of constricted) with a shorter siphonal canal, a less defi ned pattern of lines, and the slightly larger adult size. Sinetectula shepstonensis (Tomlin, 1926)

Type locality
"Beach End near Port Shepstone".

Remarks
Sinetectula shepstonensis gen. et comb. nov. shares all characteristics with S. cinis gen. et comb. nov., apart from the presence of a labral denticle. Specimens from deep water (see Fig. 9C-G) are more slender, with a laterally more fl attened spire very similar to S. cinis gen. et comb. nov.; shallow water specimens have slightly more convex whorls. One of the specimens has the apex in rather good condition without too much erosion and shows a conical, rather high, multispiral protoconch consisting of 3 whorls with a small tip.
Sinetectula cinis gen. et comb. nov. is almost identical in sculpture but differs from S. shepstonensis gen. et comb. nov. in its rougher sculptured edge of the outer lip with a labral denticle, the slightly stronger spiral sculpture in combination with much weaker secondary spiral cords, the laterally weakly fl attened whorls (instead of convex), the slightly stretched base (instead of constricted) resulting in a slightly broader siphonal canal and a much darker colour.
Sinetectula nigricostata gen. et comb. nov. looks similar to but differs from S. shepstonensis gen. et comb. nov. in its slightly more convex whorls, the slightly fi ner spiral sculpture, the stronger axial ribs that are lower in number, the constricted base with longer siphonal canal and a much darker pattern consisting of fi ne spiral lines.

Discussion
The species that we accommodate within Sinetectula gen. nov. may look quite heterogeneous with respect to shape and colour pattern, and not all species look representative for the genus. This was already refl ected in their former, provisional placements in a number of different genera. To our advantage, S. egregia gen. et comb. nov. and S. farinosa gen. et comb. nov. form a well recognizable duo, but with a contrasting shape and protoconch, corresponding to what we may expect from variability within the group. In addition, the single shell of Sinetectula sp. non descr. from Indonesia combines features of S. egregia gen. et comb. nov. with S. nigricostata gen. et comb. nov., in line with our hypothesis that Sinetectula gen. nov. is a monophyletic group. Unfortunately, we couldn't trace any fossil record of Sinetectula gen. nov. to reveal the phylogentic pattern in time.
Further study will provide a defi nitive answer as to wether also Tritonidea castanea from the Persian Gulf and Pisania townsendi from Pakistan belong to Sinetectula gen. nov.
When at least six known species stay unrecognised as a group, then it is entirely possible that more than one species has escaped our attention. We therefore expect that additional species will become detected.