Belomitra hypsomitra, Kantor & Puillandre & Rivasseau & Bouchet, 2012

Kantor, Yuri I., Puillandre, Nicolas, Rivasseau, Audrey & Bouchet, Philippe, 2012, 3496, Zootaxa 3496, pp. 1-64 : 49-51

Belomitra hypsomitra new species

Figures 20, 29A–F, 30B

Type material: holotype MNHN 24490 (measurements: SL 18.7 mm, BWL 8.7, AL 7.3, SW 4.7 mm) .

Type locality: Fiji, Lau Group, Yagasa I., 18º43’S, 178º23’W, 392–407 m, 12 March 1999 [BORDAU 1 sta. DW1496] .

Material examined: FIJI. BORDAU 1 , sta. DW1432 , 17º20’S, 178º44’W, 477–493 m , 4 dd; sta. DW1496 , 18º43’S, 178º23’W, 392–407 m, 1 lv (holotype) .

Description (holotype, Fig. 29A–C): Shell small, solid, very slender (SW/SL 0.25), with high elevated spire, consisting of 1.5 protoconch and 7.25 slightly convex teleoconch whorls. Protoconch smooth, globose, elevated, diameter 850 µm, height 700 µm. Protoconch-teleoconch transition marked by strong orthocline rib after which teleoconch sculpture appears. Suture shallowly adpressed. Last whorl 0.46 SL, slightly convex. No subsutural ramp. Besides inconspicuous growth lines, axial sculpture consisting of narrow, closely spaced, and very weakly recurved, nearly orthocline, ribs. Number of ribs increasing from 12 on first teleoconch whorl to 26 on penultimate, and 33 on last whorl, extending over all whorl height on spire whorls, becoming obsolete on shell base, and hardly discernible on canal. Spiral sculpture of distinct, raised, narrow, and sub-equal cords, covering the entire shell surface, 10 on penultimate and 28 on last whorl. Cords more closely spaced on shell periphery, interspaces narrower than cords width, but more broadly spaced on base of canal. One slightly more pronounced adapical cord marks an indistinct shoulder. Cords form well pronounced knobs at intersections with axial ribs, producing an overall beaded shell appearance. Aperture 0.39 of SL, narrow-elongate, gradually passing into short and broad siphonal canal, slightly recurved to left. Outer lip thin, evenly convex. Columella slightly convex, with five poorly developed plaits, adapical one smallest. Callus narrow, of thin transparent glaze overlying parietal region. Siphonal notch absent. Shell colour very light yellow with greenish tint. Periostracum poorly developed, present in interspaces between cords and ribs, but eroded on knobs.

Holotype is an adult male, with medium long, simple penis, tapering towards tip and without defined papilla. The radula ( Fig. 30B) consists of approximately 80 rows of teeth, 7 nascent, and 10–11 anteriormost ones strongly damaged. Radula 1.44 mm long (0.19 AL), narrow, about 75 µm in width (1.02% of AL). Lateral teeth about 65 µm in maximum length (0.89% of AL), with narrow base, attached to the membrane at an angle of 7–12º to the longitudinal axis. Lateral teeth bicuspid, inner cusp more than twice as long as the outer one. Rachidian teeth closely spaced and cusps overlapping previous row; tooth base nearly triangular, with broader anterior edge which is hardly discernible from membrane; three closely spaced, rather delicate, cusps, central one twice as long as the lateral ones, emanating from posterior edge of tooth base.

Distribution: Known from two stations off Fiji, alive in 392–407 m, shells to 477 m ( Fig. 20).

Etymology: From the Greek hypselos, meaning high, and suffix - mitra, by reference to the high, mitriform shell shape.

Remarks: The other specimens of the species are very similar in shell outline, and differ only in having less pronounced knobs at the intersections of spiral cords and axial ribs.

Belomitra hypsomitra is most similar to B. brachymitra . The differences are discussed in the Remarks section of the latter species. B. hypsomitra also has somewhat similar sculpture pattern to B. radula , but differs in having a more slender shell, a beaded shell surface, better pronounced columellar plaits, and in the nearly complete absence of a subsutural ramp.

Through its very slender shell, sculpture, and relatively well developed columellar plaits, Belomitra hypsomitra superficially resembles representatives of the family Costellariidae . Nevertheless the radula leaves no doubt about its taxonomic position.

Three of five specimens were drilled by an unknown predator, with up to 7 holes in the one shell ( Fig. 29E–F).