Belomitra paschalis ( Thiele, 1925 ) Kantor & Puillandre & Rivasseau & Bouchet, 2012

Kantor, Yuri I., Puillandre, Nicolas, Rivasseau, Audrey & Bouchet, Philippe, 2012, 3496, Zootaxa 3496, pp. 1-64 : 17-18

Belomitra paschalis ( Thiele, 1925) comb. nov.

Figures 5, 7, 8A–D

Mangelia paschalis Thiele 1925: 244 , pl. 26, fig. 23.

Bathyclionella paschalis ( Thiele, 1925) — Powell 1966: 139.

Belomitra pacifica ( Dall, 1908) . Bouchet and Warén 1976: 473 (in part), fig. 69 (holotype of Mangelia paschalis illustrated).

Holotype: ZMB /Moll—109461 ( Fig. 7 A).

Type locality: Tanzania, Zanzibar Channel , 5°27'9"S, 39°18'8"E, 463 m [ Valdivia , sta. 245] .

Material examined: MOZAMBIQUE. MAINBAZA, sta. CP3138, 25º13’S, 35º21’E, 700–707 m, 4 dd, 1 lv (sequenced MNHN IM200918853 ); CP3140 , 23º33’S, 36º02’E, 886–898 m, 1 dd, 1 lv; sta. CP3141, 23º33’S, 35º55’E, 648–698 m, 6 dd; sta. CP3148, 21º32’S, 35º47’E, 768–787 m, 1 dd, 1 lv (sequenced MNHN IM200918854 ); sta. CC3152 , 19º34’S, 36º45’E, 443–445 m, 1 dd; sta. CC3153 , 19º35’S, 36º46’E, 518–524 m, 5 dd; sta. CC3154 , 19º36’S, 36º47’E, 636 m, 4 dd, 1 lv (sequenced MNHN IM200918855 ); sta. CC3155 , 19º38’S, 36º49’E, 825–827 m, 3 dd; sta. CC3166 , 24º22’S, 35º42’E, 708–715 m, 2 dd, 1 lv; sta. CC3171 , 25º59’S, 34º42’E, 771–776 m, 1 lv; sta. CC3172 , 25º59’S, 34º35’E, 630–638 m, 1 lv (sequenced MNHN IM200918856 ) .

Description: Shell medium-sized, turriform, with moderately elevated spire, consisting of up to 5 convex teleoconch whorls. Last whorl high, 0.62–0.66 SL. Protoconch comparatively large, diameter ca 1200 µm, height ca 1000 µm, bulbous, consists of 1.5 whorls, covered with inconspicuous micropits. Suture narrow, deeply impressed. Subsutural ramp well pronounced, narrow, concave, delimitated on shoulder by row of sharp knobs formed by thickened axial ribs. Another row of knobs below suture. Axial sculpture, besides inconspicuous growth lines, of sharp, narrow, closely spaced, sinuous and nearly prosocline ribs, 15–20 on last whorl and 13–17 on penultimate one. Ribs usually less pronounced on ramp, running from suture to suture on spire whorls and becoming obsolete on shell base. Spiral sculpture of distinct, low, narrow cords, covering entire shell surface. Cords varying in size and irregularly spaced, more pronounced and broadly spaced on canal. On intersection with axial ribs cords become broader and form small rounded knobs. Aperture medium high, elongate oval, poorly differentiated from canal. Outer lip thin, concave adapically and convex and evenly rounded abapically. Columella nearly straight, smooth. Callus narrow, of thin transparent glaze overlying parietal region. Siphonal notch absent. Canal short, broad, curved abaxially. Shell colour off white. Periostracum indistinct and transparent. Operculum small, leaf-shaped, with terminal oval nucleus, strongly curved to left.

Radula ( Fig. 8A–D) very similar in the two specimens examined, long and narrow, of about 70 (specimen with SL 10.1 mm — Fig. 7F) to 85 rows of teeth (specimen with SL 15.0 mm— Fig. 7G), 15–18 nascent, from 1.5 to 2.1 mm long (0.28 of AL and 0.14–0.15 of SL), only about 50–70 µm wide (0.93%–0.94% of AL). Lateral teeth about 45–65 µm in maximum length, with narrow base, bicuspid, inner cusp slightly longer than outer one. Rachidian teeth closely spaced and cusps slightly overlaping previous row; tooth base nearly rectangular, with narrow and rather deep triangular notch on anterior edge. Three closely spaced rather delicate cusps (central longest), emanating from posterior edge of tooth base.

Distribution: East Africa, from Zanzibar to Mozambique Channel, alive in 636–886 m, shells in 445–886 m ( Fig. 5).

Remarks: These collections represent the first time that Belomitra paschalis has been collected since its original description. It is common off southern Mozambique, more than 20 degrees south of the type locality. Bouchet and Warén (1986) were the first to allocate the species to Belomitra , but synonymized it with Belomitra pacifica ( Dall, 1908) . The large material accumulated in the last couple of decades demonstrates the separate specific status of B. paschalis , which is readily distinguished from any others in the western Indian Ocean by its small size (less than 15 mm, usually less than 10 mm) and characteristic, relatively short shell with strongly angulated shoulder and row of broadly spaced sharp knobs on shoulder. It has a slight resemblance only to Belomitra minutula n. sp., that differs from it by its even smaller size (shell attaining only 8.5 mm in length), and by having strongly unequal cusps on the lateral teeth (vs nearly equal cusps in B. paschalis ).

A specimen of B. paschalis from MAINBAZA sta. CC3172 ( Fig. 7G) was slightly different from the others, being about 1.5 times larger and having more smooth axial ribs; it also lacks an operculum, although it is not clear whether it was not lost due to trauma. However, molecular analysis indicates that it is conspecific with other, more typical specimens from the same cruise, and its radula also does not differ significantly.