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

Kantor, Yuri I., Puillandre, Nicolas, Rivasseau, Audrey & Bouchet, Philippe, 2012, 3496, Zootaxa 3496, pp. 1-64 : 54-58

Belomitra granulata new species

Figures 11, 33, 34

Type material: holotype MNHN 24501 (measurements: SL 7.3 mm, BWL 5.0, AL 3.9, SW 3.1 mm) and 5 paratypes MNHN 24502 .

Type locality: South-East of New Caledonia, 22º15’S, 167º15’E, 440 m, 5 Sept. 1985 [ BIOCAL sta. DW77 ] .

Material examined: NEW CALEDONIA. EAST COAST. LAGON, sta. 830, off Poindimié , 20º49’S, 165º19’E, 105–110 m, 2 lv, 7 dd; Vauban, sta. 2, 22º17’S, 167º14’E, 425–430 m, 8 dd ; BIOCAL, sta. DW104 , 21º31’S, 166º21’E, 375–450 m, 1 dd; sta. DW106 , 21º36’S, 166º29’E, 625–650 m, 1 dd; BIOGEOCAL, sta. KG 227, 21º33’S, 166º24’E, 500 m, 2 dd; sta. CP232, 21º34’S, 166º27’E, 760–790 m, 3 dd; sta. CP253, 21º32’S, 166º29’E, 310–315 m, 10 dd; BATHUS 1, st DW651 , 21º42’S, 166º40’E, 1080–1180 m, 27 dd; st DW654 , 21º17’S, 165º57’E, 237–298 m, 4 lv, 4 dd; st DW671 , 20º51’S, 165º28’E, 450–470 m, 1 dd, st DW683 , 20º35’S, 165º07’E, 380–400 m, 1 dd; st DW687 , 20º35’S, 165º07’E, 408–440 m, 4 dd; st DW688 , 20º33’S, 165º00’E, 270–282 m, 27 dd; st DW689 , 20º33’S, 165º00’E, 260–265 m, 1 lv; st DE 700, 20º57’S, 165º35’E, 160–222 m, 13 dd;

WEST COAST. Vauban , sta. 40, 22º30’S, 166º24’E, 250–350 m, 17 dd; BATHUS 2, sta. CP758, 22º18’S, 166º11’E, 377–386 m, 1 dd; sta. CP760, 22º19’S, 166º11’E, 455 m, 3 dd; sta. DW761 , 22º19’S, 166º11’E, 490–500 m, 2 dd ;

SOUTHERN NEW CALEDONIA. BIOCAL, sta. CP30, 23º09’S, 166º41’E, 1140 m, 1 dd; sta . DW33 , 23º10’S, 167º10’E, 675–680 m, 3 dd; sta . DW36 , 23º09’S, 167º11’E, 650–680 m, 1 dd; sta . DW38 , 23º00’S, 167º15’E, 360 m, 1 dd; sta . DW41 , 22º45’S, 167º12’E, 380–410 m, 1 dd; sta . DW44 , 22º47’S, 167º14’E, 440–450 m, 70 lv and dd; sta . DW46 , 22º53’S, 167º17’E, 570–610 m, 32 dd; sta . DW51 , 23º05’S, 167º45’E, 680–700 m, 4 dd; sta . DW56 , 23º35’S, 167º12’E, 695–705 m, 2 dd; sta. CP70, 23º25’S, 167º53’E, 965 m, 4 dd; sta. CP75, 22º19’S, 167º23’E, 825–860 m, 1 lv, 12 dd; sta . DW77 , 22º15’S, 167º15’E, 440 m, 75 lv and dd (holotype and paratypes); BATHUS 2, sta . DW715 , 22º39’S, 167º11’E, 202–227 m, 9 dd; sta . DW717 , 22º44’S, 167º17’E, 350–393 m, 13 dd; st DW719 , 22º48’S, 167º16’E, 444–445 m, 1 dd; sta . DW720 , 22º52’S, 167º16’E, 530–541 m, 6 dd; sta . DW721 , 22º54’S, 167º17’E, 525–547 m, 1dd; sta. CP723, 22º36’S, 166º26’E, 713–950 m, 1 dd; sta DW724 , 22º48’S, 167º26’E, 344–358 m, 22 dd; sta. CP725, 22º22’S, 166º14’E, 495 m, 1 dd; st DW730 , 23º03’S, 166º58’E, 397–400 m, 10 dd; st DW733 , 22º55’S, 166º49’E, 520 m, 3 dd; sta . DW739 , 22º35’S, 166º27’E, 465–525 m, 10 dd; sta . DW754 , 22º23’S, 166º13’E, 577–780 m, 3 dd; BATHUS 3, st DW809 , 23º39’S, 167º59’E, 650–730 m, 1 dd; st DW838 , 23º01’S, 166º56’E, 400–402 m, 1 lv; BIOGEOCAL, sta. KG 219, 22º39’S, 166º34’E, 570 m, 3 dd; MUSORSTOM 4, sta . DW203 , 22º36’S, 167º05’E, 105–110 m, 1 lv; sta . CC 247 , 22º09’S, 167º13’E, 435–460 m, 4 dd ; SMIB 3 , sta . DW21 , 22º59’S, 167º19’E, 525 m, 2 dd; sta . DW22 , 23º03’S, 167º19’E, 503 m, 2 dd ; SMIB 8 , sta . DW152–154 , 23º18’S, 168º05’E, 305–367 m, 1 dd; sta . DW182–184 , 23º18’S, 168º05’E, 320–367 m, 7 dd; sta . DW190 , 23º18’S, 168º05’E, 305–310 m, 3 dd; sta . DW193–196 , 22º59’S –23ºS, 168º21’E – 168º23’E, 491–558 m, 13 dd ;

NORFOLK 1, sta. DW1665 , 23º43’S, 167º43’E, 923 m , 2 dd; sta. DW1732 , 23º20’S, 168º16’E, 347–1063 m , 1 dd; NORFOLK 2, sta. DW2040 , 23º41’S, 168º01’E, 285 m , 4 dd; sta. DW2136 , 23º01’S, 168º23’E, 402–410 m , 10 dd; sta. DW2144 , 23º09’S, 167º27’E, 1004–1009 m , 7 dd; sta. DW2158 , 22º41’S, 167º14’E, 265–283 m, 3 lv ; TERRASSES, sta. DW3032 , 22º41’S, 168º58’E, 760–820 m , 1 dd; sta. DW3079 , 22º28’S, 167º29’E, 300–420 m , 1 dd; sta. DW3113 , 22º43’S, 167º16’E, 250–280 m, 5 lv .

LOYALTY RIDGE. BATHUS 3 , st DW793 , 23º47’S, 169º49’E, 731–751 m, 1 dd; MUSORSTOM 6, st DW487 , 21º23’S, 167º46’E, 500 m, 1 dd ;

CORAL SEA. LANSDOWNE BANK. EBISCO, sta. DW2631 , 21º03’S, 160º44’E, 372–404 m, 1 lv , 3 dd; sta. DW2639 , 20º47’S, 161º01’E, 289–294 m , 2 dd;

Description (holotype, Fig. 33A–C): Shell small, solid, ovate–fusiform, with medium high spire, consisting of 1.5 protoconch and 4 convex teleoconch whorls. Protoconch globose, smooth, relatively large, diameter 900 µm, elevated height 560 µm ( Fig. 33D). Protoconch-teleoconch transition marked by five distinct orthocline ribs, after which spiral ribs start. Suture shallow, impressed. Last whorl convex, high, 0.68 of SL. Subsutural ramp hardly discernible. Beside numerous inconspicuous growth lines, axial sculpture consisting of narrow, very closely spaced, prosocline ribs, of uneven width and strength, extending over total whorl height on spire whorls and to end of canal on last whorl. Interspaces between ribs usually less then half of rib width; usually 1–2 smaller riblets between two adjacent, more pronounced ribs. Number of ribs increasing from 19 on first teleoconch whorl, to 35 on penultimate, and about 50 on last whorl. Spiral sculpture of distinct, closely spaced, rounded above, spiral cords; first two upper teleoconch whorls with 4 cords, separated by narrow grooves; early on third whorl, secondary cords appear, that gradually become thicker and, on penultimate whorl, are nearly equal to primary cords, 7 in total. On last whorl (including canal), 20 cords, five lowest on canal, slightly narrower than others. At intersection with axial ribs, cords form well pronounced, rounded beads, that together are responsible for the granulated shell surface appearance. Aperture high, 0.53 of SL, narrow oval, poorly delimitated from short and broad siphonal canal, slightly recurved to left. Outer lip thin, evenly rounded. Columella slightly convex with four closely spaced distinct plaits. Callus narrow, of thin transparent glaze overlying the parietal region. Siphonal notch very shallow. Shell colour very light yellow. Periostracum thin, persisting in interspaces between axial ribs.

Although there were no preserved specimens available for anatomical studies, many were dried with the bodies inside, and some external morphology features were examined from rehydrated bodies. Contrary to all other species of Belomitra , B. granulata lacks an operculum, but possess medium-sized to very large eyes.

The radula was examined in two specimens, a paratype ( Fig. 34A–B) and a specimen from BIOCAL sta. CP75 ( Fig. 34C–D). The radula of the paratype (SL 4.9 mm, AL 2.9 mm) is moderately long, 0.63 mm long (0.21 of AL), narrow, about 35 µm in width (1.21% of AL), consisting of 45 rows of teeth, 6 nascent. Lateral teeth long, about 35 µm in maximum length (1.21% of AL), flat, with narrow base. Lateral teeth bicuspid, with stout upper cusp, and much smaller lower one, which is situated on inner side of tooth ( Fig. 34B). Rachidian teeth broadly spaced, cusps slightly overlapping previous row. Lateral margins of tooth base merge into membrane and not always visible, tooth base nearly rectangular, with shallowly arched anterior margin. Three closely spaced short cusps (central nearly twice longer than lateral ones) emanate from the posterior edge of tooth base.

Radula of second specimen (BIOCAL sta. CP75) similar to that of paratype, slightly longer (1.07 mm in length, or 0.27 of AL), consisting of 65 rows of teeth, 40 µm in width, but relatively more narrow (1.0% of AL), differing in the lower (inner) cusp of the lateral tooth being larger, a more trapezoid shape of rachidian teeth base, and cusps of rachidians more curved in profile ( Fig. 34D).

Distribution: New Caledonia proper, Norfolk Ridge, Loyalty Basin and Loyalty Ridge, Coral Sea, shells in 105–1180 m, alive in 105–860 m ( Fig. 11).

Etymology: From the Latin adjective granulatus, granular, with reference to the shell sculpture.

Remarks: This is a very variable species with a very broad bathymetric range. Shells vary in terms of slenderness, from broadly ovate ( Fig. 33N) to narrowly fusiform (e.g. Fig. 33K, L) (SW/SL varies from 0.37 to 0.55, 0.42 in holotype). Relative aperture height (AL/SL) varies from 0.46 to 0.63 (0.53 in holotype). Sculpture is also very variable in terms of prominence of axial ribs and number of spiral cords; shell can be covered by very large beads, sometimes nearly square ( Fig. 33O), or axial ribs can be broadly spaced and therefore only few pointed beads are present ( Fig. 33H, L). The protoconch also varies in diameter from 800 to 1100 µm.

Some of this variation may be related to depth. In shallow water specimens, the shells are usually more ovate, with a taller last whorl and a sculpture consisting of large, closely spaced beads ( Fig. 33M–O), whereas in most deep-water samples the specimens tend to have fewer, broadly spaced, rows of beads and an overall more slender shell ( Fig. 33I, L, K). However, at stations with a large number of specimens (eg. BIOCAL DW44 and CP75), the variations encompass the whole range for the species, with gradual transitions between very different shell types. We were not able to distinguish these different forms morphometrically. In the absence of clear discontinuities between forms, and pending material available for molecular studies, we treat Belomitra granuata as a highly variable, polymorphic species, although future studies may reveal the presence of several closely related species.

Belomitra granulata is readily distinguished from other species of the genus in its smaller size, absence of subsutural ramp, and characteristic sculpture.