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

Kantor, Yuri I., Puillandre, Nicolas, Rivasseau, Audrey & Bouchet, Philippe, 2012, 3496, Zootaxa 3496, pp. 1-64 : 41-42

Belomitra subula new species

Figures 11, 23, 24A–B

Type material: holotype MNHN 24488 (sequenced as MNHN IM200732970 ) (measurements: SL 37.3, BWL 19.6 mm, AL 14.0 mm, SW 11.0 mm), 6 paratypes MNHN 24489 (1 sequenced as MNHN IM200732971 ) .

Type locality: Solomon Islands, SW of Santa Isabel Island , 08º47.0’S, 159º37.9’E, 762–1060 m, 22 Oct. 2004 [SALOMON 2 sta. CP2182] .

Material examined: SOLOMON ISLANDS. SALOMON 1, sta. DW1773 , 08º11.0’S, 160º39.9’E, 331–397 m, 1dd; sta. DW1781 , 08º31.2’S, 160º37.7’E, 1036–1138 m, 2dd, poorly preserved; sta. CP1798, 09º21.0’S, 160º29.2’E, 513–564 m, 1 dd; sta. CP1858, 09º37.0’S, 160º41.7’E, 435–461 m, 2dd ;

SALOMON 2, sta. CP2182, 08º47.0’S, 159º37.9’E, 762–1060 m, 5 dd, 2 lv (holotype MNHN 24488 sequenced as IM200732970 , paratype MNHN 24489 sequenced as IM200732971 , 5 dd paratypes); sta. CP2197, 08º24.4’S, 159º22.5’E, 897–1057 m, 2 lv (radula and morphology examined, one specimen sequenced MNHN IM200732724 ) , 2 dd; sta. CP2241, 06º55.3’S, 156º21.2’E, 815–1000 m, 2 dd; sta. CP2247, 07º44.9’S, 156º24.7’E, 686–690 m, 1 dd; sta. CP2252, 07º28.4’S, 156º17.5’E, 1059–1109 m, 1 dd, 1 lv (specimen sequenced MNHN IM200732966 ) .

SALOMONBOA3, sta. CP2800, 08º41’S, 161º04’E, 556–864 m, 1dd.

VANUATU. BOA0, sta. CP2305, 16º37.1’S, 167º58.7’E, 604–605 m, 1 dd; sta. CP2312, 14º44.5’S, 167º08.4’E, 964–1036 m, 1 dd; sta. CP2330, 15º44.0’S, 167º01.8’E, 295–890 m, 2 dd; BOA 1, sta. CP2412, 15º44.0’S, 187º02’E, 373–800 m, 1 dd; sta. CP2452, 16º00’S, 166º41’E, 1150–1273 m, 1 dd; sta. CP2468, 16º31’S, 167º56’E, 550–565 m, 1 dd .

SOUTH-WEST PACIFIC. Tuscarora Bank. MUSORSTOM 7, sta. DW560 , 11º47’S, 178º20’W, 697–702 m, 1 lv (radula examined) .

Description (holotype, Fig. 23A–C): Shell medium-sized, solid, turriform, with high elevated spire, consisting of 10+ slightly convex teleoconch whorls. Protoconch and adapical teleoconch whorls eroded. Suture shallowly adpressed. Last whorl medium high, 0.52 of SL, evenly convex. Subsutural ramp present on all teleoconch whorls, slightly concave. Besides numerous thin growth lines, axial sculpture consisting of narrow, closely spaced, low, and weakly recurved, nearly orthocline, ribs. Ribs poorly pronounced on subsutural ramp. Number of ribs increasing from 11 on first preserved teleoconch whorl to 21 on penultimate and 27 on last whorl. Ribs becoming obsolete on shell base. Spiral sculpture of distinct, narrow, irregularly spaced, cords of uneven strength, covering entire shell surface. Interspaces between cords 1–4 times cords width. Cords better pronounced on axial ribs, where they become slightly wider and form small beads, better pronounced immediately abapically of ramp. On subsutural ramp cords much more narrow and broadly spaced. Two to three cords on subsutural ramp of adapical teleoconch whorls, 4 on penultimate whorl and 5 on last whorl. Thin indistinct spiral riblets present between cords on subsutural ramp. Four cords below ramp on teleoconch whorls and 18 on last whorl. Aperture medium high, 0.37 of SL, narrow-elongate, poorly delimitated from short and broad siphonal canal, slightly recurved to left. Outer lip thin, very slightly concave adapically and convex and evenly rounded abapically. Columella convex, with two very weak indistinct plaits, visible when shell is turned counter-clockwise. Callus narrow, of thin transparent glaze overlying parietal region. Siphonal notch very shallow, nearly obsolete. Shell colour off-white. Periostracum thin, tightly adhering, very light olive.

Operculum large, narrow leaf-shaped, with terminal abraded nucleus turned to left.

Morphology of one adult female specimen (sta. CP2197, Fig. 23H) was examined. Only anterior part of body was available for study. General arrangement of foregut is similar to that of Belomitra nesiotica . The main difference is that the proboscis was thin and narrow and folded several times within rhynchodaeum, its length is 27.5 mm (0.5 of SL and 1.2 of AL).

Radula ( Fig. 24A) strongly cuticularized, brown, long, consisting of approximately 65 rows of teeth, 6 nascent, 5.3 mm long (0.23 AL), narrow, about 210 µm in width (0.9% of AL). Lateral teeth about 180 µm in maximum length (0.8% of AL), with narrow base. Lateral teeth bicuspid, inner cusp slightly narrower than outer one. Rachidian teeth closely spaced and cusps overlaping previous row. Tooth base trapezoid, with notched broader anterior edge. Three closely spaced strong cusps (central longest) emanate from posterior edge of tooth base.

Distribution: From the Solomon Islands to Vanuatu and Tuscarora Bank in the Southwest Pacific, alive in 760–1110 m, shells in 435–1140 m ( Fig. 11).

Etymology: subula (Latin) —an awl, reflecting the overall shell shape; used as a noun in apposition.

Remarks: Belomitra subula is a large species attaining 53 mm. It is rather variable in terms of shell outline and the smaller specimens proportionally have a more constricted shell base. The holotype seems to be the only specimen that has somewhat distinct, although very weak, columellar plaits.

The specimens from Vanuatu (all dead collected) have a slightly more slender shell outline, and in the absence of molecular data we consider them conspecific with specimens from the Solomon Islands. A single subadult specimen was collected alive on Tuscarora Bank; it is very similar in shell shape and radular characters to specimens from the Solomons, and we consider them conspecific. It is the only specimen that has an intact protoconch, which is typical for the genus, globose, of 1.5 convex whorls, diameter ca 1000 µm, height 800 µm, covered with thin distinct spiral cords. Its radula is slightly smaller than in specimens from the Solomons, about 2 mm in length (0.19 of AL), width about 80 µm (0.8% of AL), very similar in teeth shape ( Fig. 24B) to specimens from the Solomons.

Belomitra subula is morphologically most similar to B. nesiotica , which is confirmed by the molecular data. It differs by having a more slender shell with less convex whorls and a lower last whorl, by the absence of a row of well-defined knobs just abapically of the suture, and by a less curved siphonal canal.