Belomitra brachytoma ( Schepman, 1913 ) Kantor & Puillandre & Rivasseau & Bouchet, 2012

Kantor, Yuri I., Puillandre, Nicolas, Rivasseau, Audrey & Bouchet, Philippe, 2012, 3496, Zootaxa 3496, pp. 1-64 : 28-32

Belomitra brachytoma ( Schepman, 1913) comb. nov.

Figures 11, 15, 16

Surcula brachytoma Schepman, 1913: 424 , pl. 27, fig. 11.

Surcula brachytoma — van der Bijl et al. 2010: 43, pl. 27 fig. 11 [facsimile of Schepman's original plate].

Bathyclionella brachytoma — Powell 1966: 139.

Belomitra pacifica ( Dall, 1908) [part]— Bouchet and Warén 1986: 473, fig. 68 (syntype illustrated).

Type material: 2 syntypes ( Fig. 15A), formerly Zoological Museum of Amsterdam, now Naturalis, Leiden.

Type locality: Indonesia. SIBOGA, sta. 284, 08º43.1’S, 127º16.7’E, 828 m ; sta. 300, 10º48.6’S, 123º23.1’E, 918 m.

Material examined: SOLOMON ISLANDS. SALOMON 1 sta. DW1753 , 09º02.7’S, 159º49.4’E, 1001–1012 m, 1 lv; sta. DW1772 , 08º15.8’S, 160º40.4’E, 570–756 m, 5 dd; sta. DW1775 , 08º12.6’S, 160º41.7’E, 498–600 m, 1 dd; sta. DW1781 , 08º31.2’S, 160º37.7’E, 1036–1138 m, 2 dd; sta. DW1795 , 09º18.8’S, 160º22.9’E, 442–451 m, 4 dd, 1 lv (radula prepared); sta. CP1798, 09º21.0’S, 160º29.2’E, 513–564 m, 1 dd; sta. CP1805, 09º35.0’S, 160º42.7’E, 367–500 m, 4 dd; sta. CP1808, 09º45.5’S, 160º52.5’E, 611–636 m, 1 lv, 2 dd; sta. CP1858, 09º37.0’S, 160º41.7’E, 435–461 m, 2 dd + 5 juv. +4 juvs lv; sta. CP1859, 09º32.6’S, 160º37.3’E, 283–305 m, 4 lv juv. + 1 dd ;

SALOMON 2, sta. CP2181, 08º46.9’S, 159º39.8’E, 645–840 m, 3 dd; sta. CP2184, 08º16.9’S, 159º59.7’E, 464–523 m, 12 dd, 2 lv (sequenced, MNHN IM200911057 , radula prepared and MNHN IM200732672 ); sta. CP2186, 08º17.0’S, 160º00’E, 487–541 m, 19 dd; sta. CP2187, 08º17.5’S, 159º59.8’E, 482–604 m, 10 dd; sta. CP2188, 08º17.9’S, 160º01.3’E, 495–677 m, 1 dd; sta. CP2189, 08º19.6’S, 160º01.9’E, 660–854 m, 1 lv, 1 dd; sta. CP2195, 08º25.5’S, 159º26.4’E, 543–593 m, 7 dd; sta. CP2241, 06º55.3’S, 156º21.2’E, 815–1000 m, 1 dd; sta. CP2246, 07º42.6’S, 156º24.6’E, 664–682 m, 1 dd; sta. CP2252, 07º28.4’S, 156º17.5’E, 1059–1109 m, 1 dd, 1 lv (sequenced specimen MNHN IM200732967 ); sta. CP2275, 08º40.2’S, 157º42.5’E, 1100 m, 1 dd; sta. CP2277, 08º41.2’S, 157º37.4’E, 786 m, 1 dd ;

SALOMONBOA 3, sta. CP2772, 09º25'S, 160º31’E, 456–551 m, 3 dd; sta. CP2792, 08º16'S, 160º43’E, 460–550 m, 1 dd; sta. CP2848, 09º35’S, 160º47’E, 414–456 m, 4 dd; sta. CP2849, 09º36’S, 160º46’E, 448–523 m, 9 lv and 12 dd (one sequenced MNHN IM200736003 ); sta. CP2850, 09º37’S, 160º47’E, 502–621 m, 1 dd; sta. CP2857, 09º44’S, 160º49’E, 473–505 m, 2 dd; sta. CP2858, 09º40’S, 160º45’E, 650–725 m, 5 dd .

INDONESIA. KARUBAR, sta. CP53, 08º18’S, 131º41’E, 1026–1053 m, 1 lv (radula prepared) .

PHILIPPINES. MUSORSTOM 2, sta. CP55, 13º54’N, 119º58’E, 865 m, 5 dd, 1 lv (radula prepared) .

TAIWAN. TAIWAN 2000, sta. CP32, 22º01.7’N, 120º16.4’E, 904 m, 1 dd, 1 lv (radula prepared) .

Description: Shell medium-sized to large, turriform, with high, elevated spire, consisting of up to 10 convex teleoconch whorls angulated at shoulder. Last whorl medium high, 0.48–0.58 SL. Protoconch (usually eroded), not large, diameter about 850 µm, height ca 800 µm, bulbous, of 1.5 whorls, covered with fine spiral striations. Suture narrow, shallowly impressed. Subsutural ramp well pronounced, narrow, concave, delimitated on shoulder by row of defined rounded knobs, formed by thickened axial ribs. Another row of knobs just below suture. Besides inconspicuous growth lines, axial sculpture of sharp, narrow, rather widely spaced, nearly straight orthocline ribs, 11–16 on last whorl and 11–14 on penultimate one. Ribs usually less pronounced to complete absent on ramp, becoming obsolete on shell base. Spiral sculpture very variable, of low, broad, closely spaced cords, covering entire shell surface, sometimes indistinct. Cords varying in size and irregularly spaced, better pronounced on canal, more convex and broader spaced. When intersecting axial ribs, cords forming rounded knobs, from very small to large and rounded. Often fine spiral striation seen at least on some parts of shell. Aperture medium high, narrow, elongate. 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, from broad to constricted, curved to left, usually poorly differentiated from aperture. Shell colour off white to light creamy. Periostracum smooth, tightly adhering to shell, yellowish. Operculum medium-sized, leaf-shaped, with terminal oval nucleus, usually abraded.

Radulae ( Fig. 16) were studied in five specimens from different parts of the range ( Table 2). Generally radula is small (constituting from 0.08 to 0.22 of AL), consisting of 30–72 rows of teeth. Rachidian teeth multicuspid, broad, their lateral edges merging into subradular membrane without visible border. Number of cusps varies along the same radular membrane, sometimes in consecutive rows. In addition to main cusps there are often smaller secondary ones, and the main cusps may be subdivided into two. Radula of a specimen from Indonesia ( Fig. 16E) was extremely short compared to others and consisted of only 30 rows of teeth. It may be abnormal, but we do not have any other live collected specimen from that geographical area. Lateral teeth were similar in all specimens, with inner cusp much longer than the outer one. Anatomy of studied specimens was very similar to that of Belomitra nesiotica (see below).

Distribution: From Taiwan to Indonesia, the Philippines and Solomon Islands, alive in 430–1010 m, shells in 365–1140 m ( Fig. 11).

Remarks: Belomitra brachytoma is one of the largest species among Belomitra , reaching at least 50 mm in length in our material. It is highly variable in terms of shell outline, relative height of last whorl and aperture, and especially in sculpture. The spiral cords can vary from well pronounced to nearly obsolete and hardly discernible; knobs formed at intersection with the axial ribs also vary from very small to large and rounded; finally also the relative width of axial cords is quite variable. This variation is not geographical, and our material from the Solomons is representative of the range of the shell variability observed across the whole distribution area; the conspecificity of such specimens is backed by molecular data. The characteristic radula also confirms that we are dealing with a single, variable, and broadly distributed species, both geographically and bathymetrically (confirmed by molecular sequences of specimens from 464 and 1100 m). Because of its extensive variation in shell characters, Belomitra brachytoma can be confused with several others. In the Solomons some specimens resemble Belomitra subula , but differ in their more slender shell and less convex last whorl. The two species are readily distinguished by molecular data as well as the radula: B. brachytoma has multicuspid central teeth, while B. subula has tricuspid ones.