Belomtitra bouteti, Kantor & Puillandre & Rivasseau & Bouchet, 2012

Kantor, Yuri I., Puillandre, Nicolas, Rivasseau, Audrey & Bouchet, Philippe, 2012, 3496, Zootaxa 3496, pp. 1-64 : 36-39

Belomtitra bouteti new species

Figures 20, 21, 22

Type material: holotype MNHN 24478 (sequenced as MNHN IM200738535 ) (measurements: SL 32.6 mm, BWL 19.4 mm, AL 14.1 mm, SW 10.0 mm) and two paratypes MNHN 24479 (sequenced as MNHN IM200738528 and IM200738559 ) .

Type locality: French Polynesia, Society Islands , between Raiatea and Tahaa, 16º43’S, 151º26’W, 430 m, 16 October 2009 [TARASOC sta. 3436] .

Material examined: TUAMOTU ISLANDS. TARASOC, sta. DW3355 , 15º57’S, 147º08’W, 530–710 m , 1 dd; sta. DW3374 , 15º39’S, 146º54’W, 703–790 m , 5 dd; DW3387 , 14º57’S, 148º16’W, 550–600 m, 1 lv (sequenced specimen MNHN IM200738678 ) .

SOCIETY ISLANDS. TARASOC, sta. DW3419 , 16º33’S, 151º48’W, 798–830 m, 2 dd, 3 lv (sequenced specimen MNHN IM200738522 ); sta. DW3420 , 16º46’S, 151º04’W, 550 m, 4 dd; sta. DW3421 , 16º46’S, 151º04’W, 782–847 m, 3 dd; sta. DW3425 , 16º43’S, 151º03’W, 557 m, 1 dd, 1 lv (sequenced specimen MNHN IM200739158 ); DW3426 , 16º41’S, 151º03’W, 801–874 m, 1 dd; sta. DW3429 , 16º43’S, 150º38’W, 493–540 m, 2 dd; sta. DW3430 , 16º41’S, 150º59’W, 300 m, 1 dd; sta. DW3433 , 16º41’S, 151º03’W, 1013–1158 m, 2 dd; sta. DW3434 , 16º42’S, 151º03’W, 700–785 m, 2 dd, 3 lv (two sequenced specimens MNHN IM200738536 , IM200738607 ); sta. DW3435 , 16º41’S, 151º02’W, 500–612 m, 2 dd; sta. DW3436 , 16º43’S, 151º26’W, 430 m, 7 dd, 3 lv (sequenced specimens, holotype MNHN IM200738535 and paratypes MNHN IM200738528 and IM200738559 ); DW3437 , 16º41’S, 151º26’W, 440–560 m, 1 dd; sta. DW3438 , 16º41’S, 151º26’W, 638–700 m, 15 dd, 2 lv; sta. DW3439 , 16º43’S, 151º26’W, 800 m, 5 dd; sta. DW3440 , 16º40’S, 151º25’W, 650–800 m, 8 dd; sta. DW3442 , 16º41’S, 151º26’W, 515–550 m, 2 dd; sta. DW3451 , 16º53’S, 151º21’W, 440–490 m, 11 dd; sta. DW3452 , 16º51’S, 151º19’W, 600–705 m, 1 dd; sta. DW3455 , 16º52’S, 151º20’W, 430–527 m, 1 dd; sta. DW3457 , 16º45’S, 151º24’W, 520–572 m, 11 dd, 1 lv (radula prepared); sta. DW3459 , 17º28’S, 149º48’W, 485–560 m, 10 dd, 1 lv (sequenced specimen MNHN IM200738608 ); sta. DW3460 , 17º28’S, 149º50’W, 660–680 m, 5 dd; sta. DW3461 , 17º27’S, 149º49’W, 844–877 m, 2 dd; sta. DW3462 , 17º27’S, 149º50’W, 1000–1155 m, 1 dd; sta. DW3465 , 17º34’S, 149º54’W, 600–650 m, 1 dd; sta. DW3474 , 17º28’S, 149º50’W, 720 m, 8 dd, 1 lv (radula prepared); sta. DW3478 , 17º31’S, 149º45’W, 678–810 m, 1 dd; sta. DW3487 , 17º47’S, 149º21’W, 400–440 m, 2 dd; sta. DW3490 , 17º48’S, 149º23’W, 720–1000 m, 2 dd; sta. DW3499 , 17º41’S, 149º17’W, 550–700 m, 1 dd; sta. DW3500 , 17º38’S, 149º17’W, 630–680 m, 1 dd; sta. DW3504 , 17º37’S, 149º38’W, 455–650 m, 2 dd .

SOUTH-WEST PACIFIC. Combe Bank. MUSORSTOM 7, sta. DW540 , 12º27’S, 177º28’W, 600 m, 1 dd .

Description (holotype, Fig. 21A–D): Shell medium-sized, solid, elongate, fusiform, with elevated spire, consisting of ca. 1.5 protoconch and 8.5 moderately convex teleoconch whorls, slightly angulated at shoulder. Protoconch eroded in holotype and paratypes. Protoconch-teleoconch transition marked by weak opisthocline rib. Suture deeply impressed. Last whorl high, 0.59 of SL, weakly and evenly convex. Subsutural ramp present on all teleoconch whorls, narrow, narrower and more strongly concave on adapical whorls, where it appears as a deep and narrow groove, and more weakly concave and broader on last whorl. Besides numerous thin growth lines, axial sculpture consisting of narrow, closely spaced, and nearly straight, slightly opisthocline ribs. Ribs obsolete on subsutural ramp of adapical teleoconch whorls, and very weakly pronounced on penultimate and last whorls. Number of ribs 12 on first teleoconch whorl, 12 on penultimate one and 19 on last whorl. Ribs more pronounced on spire whorls where they extend abapically to suture, becoming obsolete on shell base and canal, and very weak on posterior half of last whorl. Row of rounded knobs abapically adjacent to suture, some knobs aligned with axial ribs, some situated in interspaces between ribs. Spiral sculpture of rather low and indistinct, narrow, irregularly spaced cords covering entire shell surface. Interspaces between cords one to two times cords width. Cords better pronounced on axial ribs, where they become slightly wider and form indistinct beads. Cords absent on subsutural ramp of adapical 4 teleoconch whorls, 3–4 weak cords on ramp of abapical whorls. 8–9 cords below ramp of adapical teleoconch whorls, 11 on penultimate whorl, 29 on last whorl. Aperture medium high, 0.43 of SL, narrowelongate, poorly delimitated from short and broad, nearly straight, siphonal canal. Outer lip thin, very slightly concave adapically and slightly convex and evenly rounded abapically. Columella nearly straight, with 3 weak plaits ( Fig. 21D). Callus narrow, of thin transparent glaze overlying the parietal region. Siphonal notch absent. Shell colour off-white. Periostracum thin, yellowish, persisting between axial ribs.

Anatomy of holotype (male) essentially similar to that of B. nesiotica . Differences are the longer and more slender cephalic tentacles, thinner anterior oesophagus, and very poorly developed valve of Leiblein.

Radula of holotype ( Fig. 22A–B) medium long, consisting of 70 rows of teeth, about 10 nascent, 3 mm long (0.21 AL), narrow, about 145 µm in width (1,02% of AL). Lateral teeth about 100 µm in maximum length (0.71% of AL), with narrow base. Lateral teeth bicuspid, cusps nearly equal in length. Rachidian teeth closely spaced, cusps overlapping previous row. Tooth base trapezoidal, with arcuate broader anterior edge. Three closely spaced strong cusps (central longest) emanate from posterior edge of tooth base.

Distribution: From Society and Tuamotu Islands ( French Polynesia) to perhaps northeast of Fiji (Combe Bank; see Remarks below), alive in 430–830 m, shells in 300–1158 m ( Fig. 20).

Etymology: the species is named after Michel Boutet, of Papara, Tahiti, co-author of the current reference checklist of the marine molluscs of French Polynesia ( Tröndlé & Boutet 2009), and who generously offered to sort all the bottom samples from the TARASOC cruise for micromolluscs.

Remarks: Paratypes are overall similar to the holotype in shell outline, although more slender. The number and prominence of columellar plaits is very variable—from complete absence, e.g. in paratype MNHN IM200738528, to 3 well developed plaits in holotype and even to 6 well pronounced plaits in paratype MNHN IM200738559 ( Fig. 21F). The radula of two additional specimens ( Fig. 22C, D) was in all details similar to the holotype. Belomitra bouteti is readily distinguished from congeners by its rather narrow shell with rather obsolete, indistinct spiral sculpture. It is co-occuring in many hauls with B. nesiotica n. sp. and is distinguished by its narrower shell, much less pronounced sculpture, weak columellar plication and nearly straight siphonal canal.

An empty shell from Combe Bank, off Wallis and Futuna in the south-west Pacific, lacks columellar plaits and has a broader shell. We attribute it with some doubt to B. bouteti .