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

Kantor, Yuri I., Puillandre, Nicolas, Rivasseau, Audrey & Bouchet, Philippe, 2012, 3496, Zootaxa 3496, pp. 1-64 : 23-26

Belomitra decapitata new species

Figures 11, 12, 13D–E

Type material: holotype MNHN 24482 (measurements: SL 20.7 mm, BWL 14.2, AL 10.7, SW 8.4 mm) ; Paratype 1 MNHN 24483 ; Paratype 2 MNHN 24484 .

Type locality: Mid-Indian Basin west of Ninety-East Ridge, 01º41’N, 87º06’E, 4360 m, 1 Aug. 1981 [SAFARI 2 sta. CP11] .

Material examined: INDIAN OCEAN. SAFARI 1, sta. CP07, 30º47’S, 48º20’E, 4245–4400 m, 1 lv (paratype 1; radula examined); SAFARI 2, sta. CP11, 01º41’N, 87º06’E, 4360 m, 1 lv (holotype).

NEW CALEDONIA. BIOCAL, sta. CP17, 20º35’S, 167º25’E, 3680 m, 1 dd (paratype 2) .

Description (holotype, Fig. 12A–C): Shell thin but solid, turriform, with high elevated spire, consisting of 4+ convex whorls. Apical whorls decollated. Suture impressed. Subsutural ramp well pronounced, narrow, concave, delimitated by a beaded subsutural cord and a row of rounded oval beads formed by intersection of axial ribs and shoulder cord. Beside inconspicuous growth lines, axial sculpture consisting of sharp, narrow, closely spaced, and very weakly recurved, prosocline ribs, 22 on penultimate and 25 on last whorls, extending over whole height of spire whorls and becoming obsolete on shell base at onset of siphonal canal. Spiral sculpture of distinct, low, narrow cords, poorly pronounced or absent on subsutural ramp, closely spaced (interspaces less than half of cords width) on periphery of spire whorls and adapical part of last whorl, and becoming more broadly spaced on shell base and canal (interspaces reaching or slightly exceeding cords width). Aperture medium high, elongate oval. Outer lip thin, concave adapically, convex and evenly rounded abapically. Columella nearly straight, smooth, without plaits, with strong siphonal fold. Callus narrow, of thin transparent glaze overlying parietal region. Siphonal notch absent. Canal short, broad, strongly curved to left. Shell colour off-white. Periostracum thin, greenish, smooth, tightly adherent, glossy on axial ribs and mat in interspaces. Operculum leaf-shaped, with eroded terminal nucleus.

The radula of paratype 1 ( Fig. 13D–E) consisted of approximately 60 rows of teeth, 1.87 mm long (0.17 AL), narrow, about 140 µm in width (1.3% of AL). Lateral teeth about 85 µm in maximum length (0.8% of AL), with narrow base, attached to the membrane at 4–7º to longitudinal axis, with narrow base. Lateral teeth bicuspid, inner cusp longer than outer one. Rachidian teeth closely spaced, cusps overlapping previous row. Tooth base trapezoidal, with slightly notched broader anterior edge, which is better seen when tooth is not overlapped by the next row ( Fig. 13D). Three closely spaced, rather delicate, cusps (central one twice longer than lateral ones) emanate from the posterior edge of tooth base.

Distribution: The abyssal species has a very broad distribution, from the western part of the Indian Ocean to New Caledonia, alive in 3680–4400 m ( Fig. 11).

Etymology: From the Latin adjective decapitatus, meaning without head, by reference to the decollation of upper whorls in all available specimens, no doubt as a result of dissolution by deep-sea bottom water below the aragonitic compensation depth.

Remarks: The two paratypes are similar in all respects to the holotype. Belomitra decapitata is rather distinct in the combination of shape with numerous, well pronounced axial ribs, and the thin and fragile shell. It has some resemblance to Belomitra admete , the differences are discussed in the Remarks section of that species.