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

Kantor, Yuri I., Puillandre, Nicolas, Rivasseau, Audrey & Bouchet, Philippe, 2012, 3496, Zootaxa 3496, pp. 1-64 : 18-20

Belomitra comitas new species

Figures 5, 8E–F, 9

Belomitra pacifica ( Dall, 1908) — Bouchet and Warén 1986 (part.): 473, fig. 70.

Type material: holotype MNHN 24477 (measurements: SL 45.1 mm, BWL 24.0, AL 18.8, SW 12.7 mm).

Type locality: North-western Madagascar, 13º01’S, 48º01’E, 1075–1110 m, 21 Jan. 1975 [ R / V Vauban sta. 135] .

Material examined: NORTH-WESTERN MADAGASCAR. R / V Vauban , sta. 135, 13º01’S, 48º01’E, 1075–1110 m, 1 lv (holotype); 17º50’S, 43º07’E, 1475–1530 m, 1 dd; MIRIKY, sta. CP3278, 15º24’S, 45º56’E, 750–780 m, 2 dd .

PHILIPPINES, EAST OF LUZON ISLAND, AURORA 2007, sta. CP2685, 14º59.6’N, 123º5.9’E, 1155–1302 m, 1 dd; sta. CP2686, 14º56.2’N, 123º9.4’E, 996–1037 m, 1 dd; sta. CP2690, 14º57.8’N, 123º2.9’E, 1071–1147 m, 10 dd; sta . CC 2704 , 15º2.7’N, 123º6.8’E, 1347–1392 m, 1 dd; sta. CP2751, 15º36’N, 121º56’E, 1456–1471 m, 1 lv ( MNHN IM200734646 ); sta . CC 2752 , 15º35.9’N, 121º57.4’E, 1436– 1387 m, 2 dd .

Description (holotype, Fig. 9A–D): Shell large, solid, turriform, with high elevated spire, consisting of 10+ strongly convex teleoconch whorls, angulated at shoulder. Last whorl high, comprising 0.53 of SL, narrow. Protoconch and first teleoconch whorls eroded. Subsutural ramp well pronounced, broad, concave. Beside growth lines, axial sculpture consisting of narrow, strong, broadly spaced, sinuous, orthocline ribs, 10 on penultimate and 12 on last whorl. Ribs weak on subsutural ramp, reaching abapical suture on spire whorls, and becoming obsolete on base and canal. Some of the growth lines are thickened and form additional axial riblets, better seen on subsutural ramp and not aligned with major axial ribs. Spiral sculpture of distinct, but low, narrow cords, delimited by flat interspaces that are half or more as broad as cords width, more uneven in width and more broadly spaced on canal. Cords absent on subsutural ramp of first 6 teleoconch whorls, except one adapical that form small rounded knobs at intersections with thickened growth lines ( Fig. 9D); cords present on ramp of last four whorls, narrow, separated by interspaces up to 3 times broader than cords. Aperture narrow, elongate. Outer lip evenly convex, except for a slight concavity corresponding to the subsutural ramp. Columella nearly straight, smooth. Callus narrow, of thin transparent glaze overlying parietal region. Siphonal notch absent. Canal short, poorly delimited from aperture, slightly curved to left. Shell colour very light olive, glossy on cords and ribs. Periostracum very thin, colorless, tightly adherent, retained in interspaces between cords.

The radula of the holotype was examined by Bouchet and Warén (1986), although the illustration was not published. It is typical for the genus. Lateral teeth with narrow base and two subequal large curved cusps. Rachidian teeth tricuspid, with large and robust cusps (central largest), emanating from anterior edge of tooth base. Posterior edge of tooth base slightly arched.

Distribution: North-western Madagascar, Philippines, alive in 1075–1110 m, shells in 750–1530 m ( Fig. 5).

Etymology: The shell outline superficially recalls Comitas, a genus of Conoidea ( Pseudomelatomidae ), and the name is used as a noun in apposition.

Remarks: Beside the holotype (illustrated by Bouchet and Warén (1986) as B. pacifica ), three other dead collected worn specimens are present from Madagascar, and all are very similar to the holotype. From other species found in the western Indian Ocean, Belomitra comitas is readily distinguished by its large, narrow shell, the large number of teleoconch whorls, well pronounced and broadly spaced axial ribs, and the presence on the subsutural ramp of small knobs that are formed by thickened growth lines rather than by the axial ribs. Despite the limited material available, the rather characteristic shell outline leaves no doubt on the distinctness of this species. The only species that slightly resembles B. comitas in shell outline is B. brachytoma . Nevertheless B. comitas can be readily distinguished by the absence of distinct knobs on the shoulder and in having tricuspid (vs multicuspid) rachidian radular teeth.

Several similar specimens were collected at 1070–1470 m in the Philippines ( Fig. 9H – L); the largest has SL 61.9 mm (protoconch and upper teleoconch whorls eroded). They show a rather high variability in shell shape, some of them being significantly broader than the specimens from Madagascar ( Fig. 9K). Pending the collection of live-taken material available for sequencing, we tentatively consider the Philippines population as conspecific with Madagascar B. comitas . The radula ( Fig. 8E–F) was examined in one of them (shell in Fig. 9L) and it was found to be similar to that of the holotype; it has 65 rows of teeth, 3 mm long (0.21 AL), narrow, about 100 µm in width (0.71% of AL). Lateral teeth about 110 µm in maximum length (0.78% of AL), with narrow base. Lateral teeth bicuspid, inner cusp slightly longer than outer one. Rachidian teeth closely spaced and significantly overlapping each other, narrow. Tooth base with strongly notched anterior edge. Three closely spaced, robust cusps, recurved in side view, central longest, emanate from the anterior edge of tooth base.

One specimen having general resemblance to B. comitas was collected in the Coral Sea in 970 m ( Fig. 9M). Based on shell shape and sculpture, we attribute it with doubts to B. comitas .