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

Kantor, Yuri I., Puillandre, Nicolas, Rivasseau, Audrey & Bouchet, Philippe, 2012, 3496, Zootaxa 3496, pp. 1-64 : 43-44

Belomitra caudata new species

Figures 20, 24C–D, 25

Type material: Holotype MNHN 24493 (sequenced as IM200732910 ) (measurements: SL 52.5 mm, BWL 28.3 mm, AL 20.7 mm, BWL 15.6 mm), paratype MNHN 24494 (sequenced as MNHN IM200911063 ).

Type locality: Philippines, Sulu Sea , 08º51.3’N, 122º58.9’E, 2307–2323 m, 29 May 2005 [PANGLAO 2005 sta. CP2387] .

Description (holotype, Fig 25A–C): Shell large, solid, turriform, with high elevated spire, consisting of 8+ strongly convex whorls, angulated at periphery. Protoconch and adapical teleoconch whorls eroded. Suture adpressed, almost canaliculate. Last whorl medium high, 0.53 of SL, evenly convex. Subsutural ramp very broad, present on all whorls, occupying about half of whorl height, very slightly concave on adapical whorls and nearly flat on penultimate and last whorls. Besides numerous thin growth lines, axial sculpture consisting of broadly spaced, low, recurved, orthocline ribs, poorly pronounced on subsutural ramp. Number of ribs increasing from 12 on first preserved teleoconch whorl to 13 on penultimate, and 22 on last whorl. Ribs becoming obsolete on canal. Spiral sculpture of indistinct, narrow and low, irregularly spaced, cords of uneven size, covering entire shell surface, in addition to very thin spiral striation. Interspaces between cords 1 to 4 times broader than cords. On adapical teleoconch whorls, cords forming small knobs at intersections with axial ribs below subsutural ramp. Stronger cord forming larger knobs bordering abapical margin of subsutural ramp. Four to six narrow cords on subsutural ramp. Thin cord forming small distinct knobs abapically of suture, some on the intersections with axial ribs, some in interspaces between ribs; 29 such knobs on penultimate whorl. Three to four cords below ramp of spire whorls and 30 on last whorl. Cords much more closely spaced on canal. Aperture medium high, 0.39 of SL, elongate, poorly delimitated from short and broad siphonal canal, slightly recurved to left. Outer lip thin, very slightly concave, nearly straight adapically and convex and evenly rounded abapically. Columella convex, smooth. Callus narrow, of thin transparent glaze overlying parietal region. Lowest part of canal chipped, siphonal notch probably absent. Shell colour greyish. Periostracum thin, tightly adhering, very light olive.

Distribution: Only known from the type locality in the Sulu Sea ( Fig. 20).

Etymology: Latin adjective caudatus —furnished with a tail, by reference to the long siphonal canal.

Remarks: The paratype, the only known other specimen, is very similar to the holotype in shell characters, with a smoother abapical delimitation of the subsutural ramp. Operculum rather long (12 mm) but narrow (3.9 mm), with terminal abraded nucleus slightly turned to the left and numerous distinct growth lines.

Anatomy of the paratype is similar to that of Belomitra nesiotica , differing in relatively narrower osphradium that is one half of ctenidium width, and a much broader ctenidium, which occupies one third of mantle width. Proboscis sheath very thin and semi-transparent, except for the attachment of one major mid-ventral and two minor lateral proboscis retractors that fuse into a single large muscle joining the columellar muscle. Proboscis smooth, colorless, very long, folded within proboscis sheath several times. Total proboscis length about 25 mm, diameter 1 mm. Odontophore minute, about 1.5 mm in length, occupying the anteriormost portion of proboscis. Radular sac significantly exceeding odontophore length. Radula ( Fig. 24C–D) short, around 3.1 mm in length (0.18 of AL), of approximately 65 rows of teeth, 6 nascent; narrow, about 120 µm in width (0.68% of AL). Lateral teeth about 120 µm in maximum length (0.68% of AL), with narrow base. Lateral teeth bicuspid, with short stout cusps of similar length, outer one recurved. Rachidian teeth closely spaced and cusps overlapping previous row. Tooth base trapezoidal, short, with shallowly arcuate broader anterior edge. Three closely spaced strong cusps (central longest) emanating from posterior edge of tooth base.

By its rather smooth sculpture, Belomitra caudata is somewhat similar to B. gymnobela n. sp., differing in the much larger adult size and the much broader subsutural ramp that reaches shell periphery. Molecular data indicate that the two species are only distantly related.