Sibogasyrinx subula Kantor & Puillandre 2021, sp. nov.

Sibogasyrinx subula sp. nov. (= PSH 3)

urn:lsid:zoobank.org:act: 6A992BBF-7C62-4F15-BFCC-AD9F347ED379

Figs 4E–F, 6

Sibogasyrinx sp. – Bouchet et al. 2011: figs 11b, 12b–c.

Diagnosis

Shell large, reaching 57 mm in length, narrowly fusiform, with concave, nearly smooth subsutural ramp with darker subsutural band on posterior half of last whorl and strong nodules on shoulder. Spiral sculpture of distinct, closely spaced cords below subsutural ramp. Radula with central tooth and duplex marginal teeth.

Etymology

Latin ‘ subula ’ (noun in apposition), meaning ‘awl’, with reference to the general appearance of the spire.

Material examined

Holotype SOLOMON ISLANDS • SE of Sta Isabel I.; 08°17′ S, 160°00′ E; depth 482–604 m; SALOMON 2, stn CP2187; MNHN-IM-2007-42530.

Other material (all sequenced)

PAPUA NEW GUINEA • 1 lv; 05°39′ S, 153°59′ E; depth 654–660 m; BIOPAPUA, stn CP3750; MNHN-IM-2009-17048 • 1 lv; New Ireland; 02°13′ S, 150°12′ E; depth 564–743 m; KAVIENG 2014, stn CP4448; MNHN-IM-2013-58409.

SOLOMON ISLANDS • 2 lv; SE of Sta Isabel I.; 08°17′ S, 160°00′ E; depth 464–523 m; SALOMON 2, stn CP2184; MNHN-IM-2009-13567, MNHN-IM-2009-13568 • 1 lv; SW of Sta Isabel I.; 08°25′ S, 159°27′ E; depth 440–521 m; SALOMON 2, stn CP2194; MNHN-IM-2007-42533 • 1 lv; 08°41′ S, 157°38′ E; depth 814–980 m; SALOMON 2, stn CP2276; MNHN-IM-2007-42517.

VANUATU • 4 lv; 15°00′ S, 166°55′ E; depth 630–705 m; BOA1, stn CP2432; MNHN-IM-2007-17701 to IM-2007-17704.

Description

MEASUREMENTS (holotype). SL 55 mm, AL (with canal) 31 mm, AL (without canal) 17.5 mm, SW 15.6 mm.

SHELL (holotype). Moderately thick, strong except for fragile outer lip of aperture, fusiform, with high spire and long, narrow, straight siphonal canal. Protoconch small, globose, of about 1.5 strongly convex, microshagreened whorls. Protoconch/teleoconch transition marked by arcuate axial rib and appearance of definitive sculpture. Protoconch diameter 1.0 mm, height 0.79 mm. Teleoconch whorls angular at shoulder. Teleoconch comprising just under 10 whorls in total. Suture shallowly impressed, subsutural ramp broad, strongly concave. Subsutural region with a row of distinct sigmoidal nodules that correspond in shape to upper parts of thickened growth lines, about 20 on first whorl, 17–19 on second–fourth whorls, 32 on penultimate and 30 on last whorl. Subsutural ramp smooth except for subsutural row of nodules, few thickened growth lines and 3–4 very weak spiral threads on last and penultimate whorls. Shoulder with pronounced thickened and rounded nodules, weakly opisthocline on upper whorls, but more strongly inclined and confluent with growth lines on last whorl; 17 on penultimate and antepenultimate whorls and 19 on last whorl. Spiral sculpture of 4–5 moderately pronounced, narrow cords on shoulder, seen both on nodules and in their intervals, and rather distinct, weakly rounded cords below shoulder, some flattened. Single cord appears on 3rd whorl, two cords on other whorls, including penultimate one. On last whorl cords occupy entire shell below shoulder, varying in width, their intervals 1–2 times width of cords, in total 48 cords on last whorl, of which 28 on canal. Shell base gradually narrowing towards long, narrow, nearly straight siphonal canal. Aperture narrow, constricted posteriorly, with very narrow and thin parietal callus, outer lip partially broken, with rounded angle at shoulder, weakly convex below shoulder and weakly concave at transition to canal. Anal sinus moderately deep, subsutural, broadly arcuate, confluent with large forward extension of outer lip. Shell off-white, with very light yellowish subsutural band and darker subsutural band on posterior half of last whorl, protoconch light tan.

ANATOMY (n = 1, MNHN-IM-2009-13568). Head with long cylindrical tentacles, rounded on tips with closely spaced bases, eyes absent. Specimen male, with long penis with obliquely truncated tip. Seminal papilla occupies entire tip and is surrounded by circular fold. Proboscis conical, with broad base, but very narrow along most of its length. Proboscis retractors large, arranged in two bundles attached to proboscis base. Buccal mass very large and broad, nearly as long as proboscis, oesophagus forming short loop before nerve ring. Venom gland thick, medium-long and convoluted, opening dorsally into oesophagus just posterior to nerve ring. Muscular bulb very large.

RADULA (n = 3; MNHN-IM-2007-17701, MNHN-IM-2007-17703, MNHN-IM-2009-13568). All specimens with similar radular morphology, radula comprising 38–40 rows of teeth, 11–17 nascent, short, length ca 1.8 mm (11% of AL without canal). Radula width up to 310 μm (1.9% of AL without canal). Central tooth with broad, subrectangular basal plate, anteriorly overlapped by preceding tooth, borders distinct, with narrow, sharply pointed cusp. Marginal teeth with strongly thickened posterior edges, folded longitudinally (Fig. 4E–F), in all details similar to those of Sibogasyrinx cf. pyramidalis 1.

Remarks

Largest specimen attains an SL of 57.4 mm.

The other specimens are rather similar to the holotype in shell shape and sculpture. The entire subsutural ramp may be pale yellowish on the last whorl, but the subsutural zone of the posterior part of last whorl in larger specimens is always more darkly coloured than the rest of the shell. The subsutural ramp may be completely smooth or with indistinct spiral threads, the shoulder angulation on the last whorl is sometimes less distinct than in the holotype, as may be the cords below the shoulder on the penultimate whorl (up to 4).

In shell outline, the new species resembles its congener Sibogasyrinx filosa, but differs in having much less distinct spiral sculpture on the subsutural ramp, as well as in its larger size (maximal SL 57.4 mm in S. subula sp. nov. and 52 mm in S. filosa) and radular morphology. The shell shape of the new species also strongly resembles that of some species of Leucosyrinx, particularly L. verrillii (Dall, 1881) (Fig. 13A–C) and to a lesser extent the smaller specimens of Leucosyrinx sp. B and Leucosyrinx sp. G (Fig. 13D and 13I, respectively). All these species of Leucosyrinx, however, have a different radular morphology, shorter siphonal canal and, according to the molecular tree (Fig. 1) and other published Conoidea phylogenies (Puillandre et al. 2011; Abdelkrim et al. 2018), belong to a different family.

Distribution

This species is known from the Solomon Islands, Papua New Guinea and Vanuatu, and has a relatively broad bathymetric range, from 440 to 814 m.