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

Kantor, Yuri I., Puillandre, Nicolas, Rivasseau, Audrey & Bouchet, Philippe, 2012, 3496, Zootaxa 3496, pp. 1-64 : 32-36

Belomitra nesiotica new species

Figures 17, 18, 19, 20

Type material: Holotype ( Fig. 17A–C) MNHN 24491 (sequenced as MNHN IM200738503 ) (measurements: SL 33.8 mm, BWL 20.4 mm, AL 15.6 mm, SW 12.4 mm) and paratype ( Fig. 17D–E) MNHN 24492 (sequenced as MNHN IM200738517 ).

Type locality: French Polynesia, Society Islands , off Huahine, 16º42’S, 151º03’W, 700–785 m, 15 October 2009 [TARASOC sta. DW3434 ] .

Material examined: FIJI. Bligh Water. MUSORSTOM 10, sta. CP1314, 17º16.1’S, 178º14.8’E, 656–660 m, 1 dd; sta. CP1330, 17º09.5’S, 177º56.3’E, 567–699 m, 1 dd; sta. CP1342, 16º46’S, 177º39’E, 650–701 m, 1 lv; Lau Islands . BORDAU 1 . sta. DW1459 , 17º18’S, 179º33’W, 820–863 m, 1 dd subadult .

TONGA. BORDAU 2 . sta. DW 1553, 20º42’S, 174º54’W, 650–676 m, 6 dd; sta. CP1565, 20º58’S, 175º53’W, 483–531 m, 1 dd.

SOCIETY ISLANDS. TARASOC, sta. DW3413 , 16º34’S, 151º46’W, 385–486 m, 10 dd; sta. DW3415 , 16º34’S, 151º47’W, 614–730 m, 1 lv (sequenced specimen MNHN IM200738692 ); sta. DW3416 , 16º35’S, 151º44’W, 914 m, 4 dd; sta. DW3417 , 16º35’S, 151º44’W, 1013–1060 m, 1 dd; sta. DW3418 , 580– 618 m, 1 dd, 1 lv (appr. coordinates: 16º30, 151º44’W, Bora Bora); sta. DW3419 , 16º33’S, 151º48’W, 798–830 m, 2 dd, 1 lv (sequenced specimen MNHN IM200738567 ); sta. DW3420 , 16º46’S, 151º04’W, 550 m, 3 dd; sta. DW3421 , 16º46’S, 151º04’W, 782–847 m, 1 dd; sta. DW3426 , 16º41’S, 151º03’W, 801–874 m, 7 dd; sta. DW3433 , 16º41’S, 151º03’W, 1013–1158 m, 10 dd; sta. DW3434 , 16º42’S, 151º03’W, 700–785 m, 1 dd, 2 lv (two sequenced specimens MNHN IM200738503 , MNHN IM200738517 , holotype and paratype); sta. DW3436 , 16º43’S, 151º26’W, 430 m, 3 dd; sta. DW3438 , 16º41’S, 151º36’W, 638–700 m, 2 dd; sta. DW3440 , 16º40’S, 151º25’W, 650–800 m, 8 dd; sta. DW3442 , 16º41’S, 151º26’W, 515–550 m, 2 dd; sta. DW3447 , 16º42’S, 151º31’W, 620–700 m, 5 dd; sta. DW3450 , 16º40’S, 151º32’W, 705–755 m, 3 dd; sta. DW3451 , 16º53’S, 151º21’W, 440–490 m, 8 dd; sta. DW3457 , 16º45’S, 151º24’W, 520–572 m,15 dd; sta. DW3433 , 17º28’S, 149º48’W, 485–560 m, 1 dd; sta. DW3459 , 17º28’S, 149º48’W, 485–560 m, 1 dd; sta. DW3460 , 17º28’S, 149º50’W, 660–680 m, 1 dd; sta.. DW3461 , 17º27’S, 149º49’W, 844–877 m, 1 lv (sequenced MNHN IM200738482 ); sta DW3462 , 17º27’S, 149º50’W, 1000–1155 m, 9 dd; sta. DW3467 , 17º34’S, 149º54’W, 800–830 m, 2 dd; sta. DW3474 , 17º28’S, 149º50’W, 720 m, 5 dd, 1 lv; sta. DW3478 , 17º31’S, 149º45’W, 678–810 m, 3 dd; sta. DW3480 , 17º32’S, 149º45’W, 880–900 m, 1 lv (sequenced specimen MNHN IM200739270 ); sta. DW3487 , 17º47’S, 149º21’W, 400–440 m, 1 dd; sta. DW3507 , 17º35’S, 149º38’W, 480 m, 1 dd; sta. DW3500 , 17º38’S, 149º17’W, 630–680 m, 1 dd .

Description (holotype, Fig. 17A–C): Shell medium-sized, solid, turriform, with elevated spire, consisting of ca. 1.5 protoconch and 9 convex teleoconch whorls, slightly angulated at shoulder. Protoconch globose, ca 1000 µm in diameter, height 800 µm, covered by distinct fine spiral striation. Protoconch-teleoconch transition marked by weak opisthocline rib and disappearance of spiral microstriation. Suture deeply impressed. Last whorl high,

.0.60 of SL, evenly convex. Subsutural ramp present on all teleoconch whorls, strongly concave on upper whorls and more poorly concave on last whorl. Besides numerous thin growth lines, axial sculpture consisting of narrow, closely spaced and weakly recurved, nearly orthocline ribs. Ribs obsolete on subsutural ramp of upper teleoconch whorls and less pronounced, although distinct, on penultimate and last whorls. Number of ribs increases from 11 ribs on first teleoconch whorl, to 17 on penultimate and 28 on last whorl. Ribs better pronounced on spire whorls where they reach abapically to suture and become obsolete on shell base and canal. Row of rounded knobs situated just below suture, some corresponding in position to axial ribs, some situated in interspaces between ribs. Spiral sculpture of distinct, narrow, irregularly spaced cords of uneven size, covering entire shell surface. Interspaces between cords 1–3 times cord width. Cords better pronounced on axial ribs, where they become slightly wider. On posterior half of last whorl cords form knobs at intersections with axial ribs. Subsutural cord well pronounced, on third and later teleoconch whorls subsutural cord subdivided into two. Cords absent on subsutural ramp of first five teleoconch whorls, on subsequent teleoconch whorls 3 cords on ramp, and on last whorl 4 cords on ramp. On adapical teleoconch whorls 3–4 cords below ramp, 5 on penultimate whorl, and 24 on last whorl. Aperture medium high, 0.46 of SL, narrow-elongate, poorly delimitated from short and broad siphonal canal, visibly recurved to left. Outer lip thin, very slightly concave adapically and convex and evenly rounded abapically. Columella convex, smooth. Callus narrow, of thin transparent glaze overlying the parietal region. Siphonal notch very shallow, nearly obsolete. Shell colour off-white. Periostracum thin, persisting between axial ribs.

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

Radula of holotype ( Fig. 18A) short, of about 60 rows of teeth, 4.1 mm long (0.20 AL), narrow, about 160 µm wide (0,78% of AL). Lateral teeth about 170 µm in maximum length (0.8% of AL), with narrow base, bicuspid, with cusps nearly equal in length. Rachidian teeth rather broadly spaced and cusps only slightly overlapping previous row. Tooth base trapezoidal, with slightly notched broader anterior edge and rounded angles. Three closely spaced narrow cusps (central longest) emanate from posterior edge of tooth base. Radula of paratype ( Fig. 18B) is very similar, differing in slightly larger cusps of rachidian teeth.

Anatomy of paratype (MNHN 24492) ( Fig. 19): Body completely lacking pigmentation. Mantle cavity long, spanning slightly over one whorl. Mantle edge does not cover the head and the base of the penis. Head small, cephalic tentacles conical, short, without any trace of eyes ( Fig. 19B, cep.t).

Mantle ( Fig. 19C) very long, twice longer than maximum width, very thin, with mantle organs clearly visible through it. Osphradium and ctenidium long. Osphradium narrow, greenish, 6 times longer than broad. Ctenidium very long and narrow, more than 10 times longer than broad. Hypobranchial gland covered with thick layer of gelatinous mucus. Rectum filled with sediments particles.

Digestive system ( Fig. 19D). Proboscis medium long (5.5 mm), straight, with smooth walls. Proboscis sheath very thin-walled, transparent. Proboscis retractors few, attached symmetrically in the middle part of the sheath and to the walls of cephalic haemocoel ( Fig. 19D, prr). Paired salivary glands embrace proboscis laterally, left gland larger, compact posteriorly but rather loose anteriorly, where it consists of long, poorly connected, long acini. Salivary ducts rather thick ( Fig. 19D, sd), join the walls of oesophagus shortly after leaving salivary gland, in front of very large and bulbous valve of Leiblein ( Fig. 19D, vL) to follow along both sides of anterior oesophagus. Gland of Leiblein very large ( Fig. 19D, gL) and adjoining posterior part of left salivary gland. Gland of Leiblein tapering posteriorly and ending in long duct that follows to the kidney, where it terminates into an ampula. Duct of gland of Leiblein very short, hardly defined ( Fig. 19D, dgL), opening into oesophagus well behind nerve ring. Nerve ring rather small and compact. Buccal mass anterior, occupying about 1/3 of proboscis length. Odontophore as long as radular sac. Subradular cartilages fused among most of their length. Mouth opening with the shape of transversal slit.

Distribution: Society Islands to Tonga and Fiji, alive in 580–830 m, shells in 385–1160 m ( Fig. 20).

Etymology: From the Greek nesiotes, islander, in the adjectival form; with reference to the occurence of the species off islands in the South Pacific.

Remarks: In the Society Islands Belomitra nesiotica is not very variable, with slight variation in degree of slenderness. In shell sculpture it is rather similar to B. reticulata n. sp., differing by its well pronounced subsutural ramp. It is co-occuring in many hauls with Belomitra bouteti n. sp. and differs from it in having a coarser sculpture, a siphonal canal more recurved to the left, a more narrow aperture and smooth columella (very weak plications are present in B. bouteti ). Belomitra nesiotica is also very similar to B. subula , differing in having a generally smaller shell with lower spire. The specific status of Belomitra nesiotica , B. bouteti , and B. subula is confirmed by their DNA sequences.

Specimens of Belomitra nesiotica from Fiji and Tonga are very similar to specimens from the Society Islands , some of them being larger, attaining 48 mm in length. The radula of a specimen from Fiji ( Fig. 18C–D) with shell length 25.7 and aperture length 11.4 mm consists of 53 rows of teeth, 2.2 mm long (0.19 of AL), 100 µm wide (0.88% of AL). It is rather similar to the radula of the type material, differing in having more broadly spaced cusps on the rachidian teeth .