Sibogasyrinx clausura Kantor & Puillandre 2021, sp. nov.

Sibogasyrinx clausura sp. nov. (= PSH 10)

urn:lsid:zoobank.org:act: 27ED0BF0-C78A-41E1-9064-E3EB0492864A

Figs 10D–M, 11A–B

Diagnosis

Shell medium-sized, reaching 41.5 mm in length, fusiform, subsutural ramp concave on upper teleoconch whorls, weakly so on last whorl, nearly smooth (except for the axial riblets), shoulder bearing nodules on spire whorls, absent on last whorl. Spiral sculpture of weak, closely spaced cords on and below shoulder. Radula with central tooth and longitudinally folded marginal teeth with weakly thickened edges.

Etymology

Latin ‘ clausura ’ (noun in apposition), meaning ‘lockdown’, with reference to the sanitary restrictions associated with SARS-COV-2 that prevailed over much of the World when this manuscript was finalized.

Material examined

Holotype NEW CALEDONIA • Coral Sea, Coriolis Bank; 21°20′ S, 157°55′ E; depth 963–970 m; KANADEEP, stn CP4964; MNHN-IM-2013-48256.

Other material (all sequenced)

AUSTRALIA • 1 lv; New South Wales, off Byron Bay; 28°03′ S, 154°05′ E; depth 999–1013 m; R/V Investigator, cruise IN2017_ V03 _100; AMS C.519344.

NEW CALEDONIA • 1 lv; Coral Sea, Coriolis Bank; 21°21′ S, 158°00′ E; depth 978–1000 m; KANADEEP, stn CP4963; MNHN-IM-2013-48244 • 3 lv; Coral Sea, Coriolis Bank; 21°20′ S, 157°50′ E; depth 961 m; KANADEEP, stn CP4965; MNHN-IM-2013-48144, MNHN-IM-2013-48169, MNHN-IM-2013-48258 • 2 lv; Coral Sea, Coriolis Bank; 21°10′ S, 157°46′ E; depth 975–980 m; KANADEEP, stn CP4966; MNHN-IM-2013-48167, MNHN-IM-2013-48235.

SOLOMON ISLANDS • 1 lv; Sta Isabel I.; 08°47′ S, 159°38′ E; depth 762–1060 m; SALOMON 2, stn CP2182; MNHN-IM-2009-16763.

Description

MEASUREMENTS (holotype, largest specimen). SL 41.4 mm, AL (with canal) 23.0 mm, AL (without canal) 13.7 mm, SW 12.4 mm.

SHELL (holotype). Moderately thick, slightly glossy, strong except for fragile and partially broken outer aperture lip, narrowly fusiform, with high spire and moderately long, straight siphonal canal. Protoconch small, globose, of about 1.5 strongly convex, eroded whorls. Protoconch/teleoconch transition marked by strongly arcuate axial rib, corresponding to shape of growth lines, followed by 10 thinner and weaker axial ribs and rather thickened growth lines. Protoconch diameter 1.0 mm, height 0.84 mm. Spire whorls distinctly angled at shoulder, last whorl with scarcely discernible shoulder. Total teleoconch whorls just over 8. Suture shallowly impressed, subsutural ramp broad, concave, on last whorl weakly concave. Subsutural region with a row of distinct, dense, narrow, short, prosocline axial wrinkles, corresponding to upper parts of thickened growth lines, extending from suture to upper ⅓ of ramp, increasing in number from 22 on first whorl to 42 on penultimate and 50 on last whorl. Shoulder of teleoconch whorls (except last one) with a row of distinct opisthoclinely elongated nodules, extending to abapical suture and intersected by spiral cords, increasing in number from 13 on first whorl to 21 on antepenultimate and penultimate whorls. Subsutural ramp smooth except for axial wrinkles mentioned above. Spiral cords intersecting shoulder nodules beginning on 2 rd teleoconch whorls (due to corrosion of shell their number is unclear) and becoming progressively stronger, 7 on antepenultimate and 8 on penultimate whorl. Cords closely spaced with intervals about half the width of cords. On last whorl cords covering entire shell surface below indistinct shoulder, about 40 cords in total, of which 20 on canal. Cords weak, slightly wavy, very closely spaced just below suture and with intervals 0.5–1.0 times cord width on shell base and canal. Shell base gradually narrowing towards narrow, nearly straight siphonal canal. Aperture narrow, constricted posteriorly, with narrow, moderately thick parietal callus, outer lip partially broken, evenly convex and weakly concave at transition to canal. Anal sinus shallow, subsutural, broadly arcuate, confluent with large forward extension of outer lip as deduced from growth lines. Shell off-white, with slightly darker subsutural ramp, protoconch light tan. Periostracum smooth, retained between cords and ribs.

ANATOMY (n = 1; MNHN-IM-2009-16763). Male. Penis obliquely truncated at tip with short, large, conical papilla occupying entire anterior part of penis, surrounded by circular fold.Eyes present.Proboscis moderately long, conical, with expanded base. Proboscis retractors not defined, entire posterior part of proboscis base muscular. Salivary glands small, not fused, with very long ducts that run within walls of oesophagus. Buccal mass moderately large, about ⅓ of proboscis length, basal, protruding backwards beyond proboscis base, radular sac lying outside proboscis. Venom gland very large, thick and strongly convoluted, very constricted before opening into oesophagus in region of nerve ring. Muscular bulb moderately large.

RADULA (n = 1; MNHN-IM-2009-16763, AL 10.6 mm) (Fig. 11A–B). Relatively short, comprising 38 rows of teeth, 16 nascent. Radula length 1.65 mm (15.5% of AL without canal), width up to 250 μm (2.35% of AL without canal). Central tooth with basal plate, having distinct anterior and lateral borders and long, narrow, sharply-pointed cusp. Anterior margin overlapped by preceding row, posterior margin almost evenly rounded except for narrow protrusion adjoining cusp. Marginal teeth flat when formed, becoming trough-shaped with weakly thickened edges during maturation, folded longitudinally when fully formed, with both margins overlapping at tooth tip. The resulting folded tooth is moderately broad with a sharp pointed tip, border between margins appears as a narrow groove along anterior edge. Tooth folding occurs within 15–16 th row of teeth (counting from rear).

Remarks

The other specimens are very similar to the holotype in shell shape and sculpture. In some specimens there is very indistinct spiral striation on the subsutural ramp and a single very weak spiral cord may even be present.

This species is most similar to Sibogasyrinx maximei sp. nov., but differs in having more numerous and narrower subsutural axial wrinkles (50 vs 43 on last whorl and 42 vs 34 on penultimate one) and less numerous (40 vs 50) spiral cords on the last whorl, the holotypes of both species being of almost the same size. Nevertheless, S. maximei sp. nov. is only represented in our material by a single specimen and thus its intraspecific variability remains unknown. The two species are broadly sympatric in the Solomon Islands, but are clearly differentiated in our molecular analysis.

Distribution

This species occurs in the Solomon Islands, New South Wales and on the Coriolis Bank in the Coral Sea, at 762–1060 m. This bathymetric range corresponds to a single haul in the Solomon Islands, while all other specimens were collected at 960–1000 m, indicating a narrower bathymetric range for the species.