Sibogasyrinx pagodiformis, Kantor & Puillandre, 2021

Kantor, Yuri I. & Puillandre, Nicolas, 2021, Rare, deep-water and similar: revision of Sibogasyrinx (Conoidea: Cochlespiridae), European Journal of Taxonomy 773, pp. 19-60 : 51-54

Sibogasyrinx pagodiformis sp. nov. (= PSH 5)

urn:lsid:zoobank.org:act:DAA613D6-5AB6-4F89-A0AD-0C718A60307E

Figs 8F , 12A–D

Diagnosis

Shell small, reaching 29 mm in length, pagodiform, with strongly concave subsutural ramp bearing two low spiral cords and distinct subsutural nodules. Axial sculpture of distinct opisthocline ribs extending to shell base, 10–11 per whorl. Spiral sculpture of closely spaced cords on and below shoulder. Radula lacking central tooth, marginal teeth trough-shaped with thickened edges.

Etymology

The name reflects the characteristic shell shape, resembling a pagoda.

Material examined

Holotype SOLOMON ISLANDS • NW of Malaita I.; 08°28′ S, 160°32′ E; depth 1250–1402 m; SALOMONBOA 3, stn CP2789; MNHN-IM-2009-16825 .

Other material (sequenced)

VANUATU • 1 lv; E of Malekula I.; 16°00′ S, 167°38′ E; depth 1262–1285 m; SANTO 2006, stn AT139; MNHN-IM-2009-11327 .

Description

MEASUREMENTS (holotype). SL 28.8 mm, AL (with canal) 15.2 mm, AL (without canal) 9.9 mm, SW 11.9 mm.

SHELL (holotype). Moderately thick, except for fragile, partially chipped outer aperture lip; pagodiform, with moderately high spire and moderately long, narrow siphonal canal inclined to abaxially left. Protoconch missing (rendering exact an whorl count and protoconch measurements impossible), upper teleoconch whorls eroded. Teleoconch whorls rapidly increasing and strongly angled at shoulder, more than 8 remaining. Suture shallowly impressed, subsutural ramp broad, concave. A row of distinct, sharp, subsutural nodules on upper teleoconch whorls. Nodules less distinct on last three whorls and situated on short, slightly raised, prosocline axial ribs. Number of ribs on uppermost whorls indeterminate due to shell surface erosion, number of nodules per whorl increasing from 16–17 on first intact whorl to 22 on penultimate and 26 on last whorl. Subsutural ramp smooth except for nodules and two low, indistinct subsutural cords. Shoulder with pronounced, thickened, opisthocline axial ribs on all teleoconch whorls. Axial ribs on upper teleoconch whorls situated just above suture, extending to shell base on last whorl, number of ribs constant, 11–12 per whorl. Ribs intersected by closely spaced, rounded spiral cords, number increasing from 5 on uppermost remaining whorl to 10 on penultimate whorl. Last whorl with total of 38 cords, including 18 on canal. Cords narrow, their intervals 0.5–1.5 times cord width. Shell base rapidly narrowing towards narrow, moderately long siphonal canal. Aperture narrow, constricted posteriorly, with thin, moderately broad parietal callus, outer lip partially broken, convex on subsutural ramp, with rounded angle at shoulder, convex below shoulder and weakly concave at transition to canal. Anal sinus judging from growth lines shallow, subsutural, broadly arcuate. Shell flesh-coloured, with darker base, glossy. Periostracum thin, persisting in some cord intervals.

ANATOMY (n = 1; MNHN-IM-2009-11327). Female. Proboscis relatively short, straight, cylindrical. Proboscis retractors large, in two bundles attached at proboscis base. Buccal mass within proboscis, rather long, about half length of proboscis, radular sac opening on right. Venom gland very thick, not long, opening with very short constriction just posterior to nerve ring. Venom bulb moderately large, elongate.

RADULA (n = 2; MNHN-IM-2009-16825, AL 9.9 mm, IM-2009-11327, AL ca 9 mm). Relatively short, comprising 20–24 rows of teeth, 8–9 nascent. Radula length 1.1–1.6 mm (12–16% of AL without canal), tooth length 150 μm (1.7% of AL without canal). Central tooth absent. Marginal teeth trough-shaped when mature ( Fig. 8F ), with slightly thickened edges and sharp pointed tips. Teeth initially forming as a flat, elongate-oval plate, its edges gradually thickening along radular membrane and then by longitudinal folding of each tooth on 10–11 th row, counting from rear.

Remarks

The second live collected specimen has a broken shell base. In sculpture pattern it is very similar to the holotype.

The species is distinct from all congeners in having a relatively broad, pagodiform shell with a shorter canal. Conchologically the species is quite similar to Comitas paupera (Watson, 1881) , a highly variable species of uncertain generic affinity, but differing in lacking distinct spiral cords on the subsutural ramp. The lectotype and paralectotypes of the latter were illustrated by Sysoev (1996: figs 42–48). Superficially, the new species also strongly resembles a miniature copy of Leucosyrinx luzonica ( Powell, 1969) (see Kantor et al. 2018: fig. 21), but differs in the shape of the marginal radular teeth and foregut anatomy. Another species of Leucosyrinx from the Solomon Islands, Leucosyrinx sp. D , is similar to the new species in shell outline ( Fig. 13F ), differing in radular morphology.

Distribution

This species was found in the Solomon Islands and Vanuatu at 1250–1262 m.

Figures

Fig. 8. Radulae of species of Sibogasyrinx Powell, 1969. A–B. Sibogasyrinx sangeri Kantor, Fedosov & Puillandre, 2018, MNHN-IM-2009-16995 (shell seen on Fig. 7C). A. Part of radula with fully formed marginal teeth; white hollow arrow indicates overlapping edges of the tooth at its tip. B. Part of radula showing transition between unfolded (white arrow) and completely longitudinally folded (black arrow) marginal teeth (ae = anterior tooth edge; pe = posterior tooth edge). C. Sibogasyrinx filosa Ardovini, 2021, Solomon Islands, MNHN-IM-2009-16831 (shell seen Fig. 9E–F). D. Sibogasyrinx lolae sp. nov., MNHN-IM-2009-29311. E. Sibogasyrinx maximei sp. nov., holotype, MNHN-IM-2013-45883, anterior end of radula. F. Sibogasyrinx pagodiformis sp. nov., MNHN-IM-2009-11327.

Fig. 12. A–D. Sibogasyrinx pagodiformis sp. nov. A–B. Solomon Islands, holotype, MNHN- IM-2009-16825, SL 28.8 mm. C–D. Vanuatu. MNHN-IM-2009-11327, SL 24.3 mm. E–H. Sibogasyrinx elbakyanae Kantor, Puillandre & Bouchet sp. nov., holotype, Solomon Islands, MNHN-IM-2009-16834, SL 27.3 mm. H. Enlarged fragment of penultimate and antepenultimate whorls. A–G to same scale.

Fig. 13. Shells of species of Leucosyrinx Dall, 1889. A–B. Leucosyrinx verrillii (Dall, 1881), French Guiana, MNHN-IM-2013-56840, SL 25.1 mm. C. L. verrillii, French Guiana, MNHN-IM-2013-56288, SL 31.9 mm (radula seen on Fig. 11C). D–E. Leucosyrinx sp. G. D. Papua New Guinea, MNHN- IM-2009-17089, SL 32.2 mm (radula seen on Fig. 11E). E. Bismarck Sea, MNHN-IM-2013-19689, SL 47.3 mm.F. Leucosyrinx sp. D, Solomon Islands, MNHN-IM-2009-16769, SL 25 mm.G. Leucosyrinx sp. E, Madagascar, MNHN-IM-2009-16897, SL 46.1 mm. H. Leucosyrinx sp. A, Philippines, MNHN- IM-2007-42445, SL 34.1 mm. I. Leucosyrinx sp. B, Solomon Islands, MNHN IM-2009-16764, SL 29.9 mm. J. Leucosyrinx sp. C, Solomon Islands, MNHN-IM-2007-42503, SL 41.2 mm (radula seen on Fig. 11F). K. Leucosyrinx sp. F, Coral Sea, Chesterfield Plateau, MNHN-IM-2007-17846, SL 27.3 mm (radula seen on Fig. 11D). All shells to same scale.