Bolma mainbaza Alf, Maestrati & Bouchet, 2010

Herbert, David G., 2024, The Vetigastropoda (Mollusca) of Walters Shoal, with descriptions of two new genera and thirty new species, European Journal of Taxonomy 923, pp. 1-119 : 107-109

Bolma mainbaza Alf, Maestrati & Bouchet, 2010

Figs 44A–D , 45

Bolma mainbaza Alf, Maestrati & Bouchet, 2010: 95 , figs 21–24.

Type loc.: Almirante Leite Bank , 26.2° S, 35.03° E, off southern Mozambique, depth 228–230 m .

Bolma mainbaza – Alf & Kreipl 2011: 29, pl. 133 figs 2–3. — Castelin et al. 2017 (molecular sequence data).

Material examined

WALTERS SHOAL – slopes • 1 living specimen; stn DW4877; 33°10′ S, 43°49′ E; depth 217–256 m; 1 May 2017; DNA tissue sample; MNHN-IM-2013-64407 • 1 living specimen; same collection data as for preceding; DNA tissue sample; MNHN-IM-2013-64408 • 2 empty shells; same collection data as for preceding; MNHN • 2 empty shells; stn DW4878; 33°09′ S, 43°50′ E; depth 221–256 m; 1 May 2017; MNHN • 1 living specimen; stn DW4879; 33°17′ S, 43°52′ E; depth 288–300 m; 1 May 2017; DNA tissue sample; MNHN-IM-2013-64406 • 5 empty shells; same collection data as for preceding; MNHN • 1 living specimen; stn DW4880; 33°17′ S, 43°51′ E; depth 275–318 m; 1 May 2017; DNA tissue sample; MNHN-IM-2013-64416 • 1 living specimen; same collection data as for preceding; DNA tissue sample; MNHN-IM-2013-64417 • 1 living specimen; same collection data as for preceding; DNA tissue sample; MNHN-IM-2013-64418 • 9 specimens, some living; same collection data as for preceding; MNHN • 10 specimens, some living; stn DW4881; 33°16′ S, 43°50′ E; depth 377–382 m; 2 May 2017; radula SEM prep.; MNHN • 1 living specimen; stn DW4885; 33°17′ S, 43°55′ E; depth 272–380 m; 3 May 2017; DNA tissue sample; MNHN-IM-2013-64413 • 1 living specimen; same collection data as for preceding; DNA tissue sample; MNHN-IM-2013-64414 • 1 living specimen; same collection data as for preceding; DNA tissue sample; MNHN-IM-2013-64415 • 5 specimens, some living; same collection data as for preceding; MNHN • 3 empty shells; stn DW4888; 33°10′ S, 43°57′ E; depth 299–311 m; 3 May 2017; MNHN • 2 specimens, living; stn DW4889; 33°09′ S, 43°58′ E; depth 353–465 m; 3 May 2017; MNHN • 1 living specimen; stn DW4894; 33°09′ S, 43°50′ E; depth 199–261 m; 5 May 2017; DNA tissue sample; MNHN-IM-2013-64403 • 1 living specimen; same collection data as for preceding; DNA tissue sample; MNHN-IM-2013-64404 • 1 living specimen; same collection data as for preceding; DNA tissue sample; MNHN-IM-2013-64405 • 1 living specimen; same collection data as for preceding; DNA tissue sample; MNHN-IM-2013-64410 • 5 specimens, some living; same collection data as for preceding; MNHN • 3 specimens, living; stn DW4895; 33°09′ S, 43°49′ E; depth 238–283 m; 5 May 2017; MNHN .

Description

SHELL ( Fig. 44A–C ). See original description.

PROTOCONCH ( Fig. 45B ). Milky-white; diameter ± 330 μm, ca 1.25 whorls; apical bulb rounded; sculptured by irregular superficial granulation with traces of widely-spaced, subspiral threads, particularly near terminal lip; terminal lip shallowly convex and slightly flaring; junction with teleoconch clearly demarcated.

OPERCULUM ( Fig. 44D ). Subcircular, but with portion abutting columella slightly flattened; central bulge weakly pustular, with irregular concentric sculpture peripherally; uniformly white.

RADULA ( Fig. 45C–F ). Formula ∞+5+1+5+∞, length ca 8.0 mm, with 55–60 transverse rows of teeth; rows with shallow central posterior indentation. Rachidian tooth with broadly ovate base-plate and almost no cusp. Lateral teeth with base-plates broadly and roundly expanded laterally, their cusps relatively small, inner ones bluntly truncate (perhaps worn), outer ones more pointed; extensive basal overlap of rachidian and lateral teeth; lateral cusps with buttress on outer margin that extends behind shaft of outer neighbour ( Fig. 45E ). Inner marginal small, appearing to be a sixth lateral, but its shaft similar to and aligned with those of other marginals; second marginal much larger, with strong, elongatetrigonal cusp, edges of cusp smooth; remaining marginals progressively smaller, their cusps becoming more slender and developing finely toothed inner margin; outermost marginals with shorter, roundly spathulate cusps.

Distribution

Known from central and southern Mozambique, southern Madagascar and Walters Shoal. On Walters Shoal it has been found on the slopes at depths of 256–377 m (live-taken material 261–377 m); dredged on substrata of coarse sand and fine gravel, with ophiuroids, octocorals and solitary corals.

Remarks

Originally described from the Almirante Leite Bank, a seamount 250 km due east of Maputo, southern Mozambique, Bolma mainbaza has subsequently been recorded from off central Mozambique and southern Madagascar at 180–282 m (supplementary data in Castelin et al. 2017). The material from Walters Shoal here referred to this species is clearly morphologically very close to that from the type locality, but differs consistently in having fewer beaded spiral cords above the periphery on the penultimate whorl (usually only four, compared to six in the typical specimens). However, Castelin et al. (2017) found B. mainbaza to be a morphologically variable species and observed that in the genus Bolma as a whole, emphasis on traditional criteria such as shell morphology and geographic isolation can lead to inaccurate conclusions regarding species diversity. Clusters of supposedly distinct, rangerestricted species may in reality be found to belong to a smaller number of more wide-ranging species when molecular data are taken into consideration. Preliminary comparison of such data indicates that Walters Shoal specimens cluster together with B. mainbaza from the type locality, southern Madagascar and the northern Mozambique Channel (Castelin pers. com. 2023). The lower spiral cord number in Walters Shoal specimens is thus likely a reflection of regional intra-specific variation.

The relationship between B. mainbaza and the likewise variable B. bathyraphis (Smith, 1899) with its spinose synonym B. gilchristi (Sowerby III, 1903) remains to be established. No western Indian Ocean material identified as B. bathyraphis was included in the molecular analysis of Castelin et al. (2017). Bolma sabinae Alf & Kreipl, 2004 from off south-western Madagascar has a much lower spire and a dark purple-red stain on the basal callus.

Figures

Fig. 44. A–D. Bolma mainbaza Alf, Maestrati & Bouchet, 2010, Walters Shoal, stn DW4881, shell (height 23.0 mm) and operculum (maximum diameter 8.5 mm) (MNHN). E–F. Bolma recens (Dell, 1967), Walters Shoal, stn DW4890, height 19.1 mm (MNHN-IM-2013-64411, images courtesy of P. Maestrati).

Fig. 45. Bolma mainbaza Alf, Maestrati & Bouchet, 2010. A. Spinose juvenile shell, Walters Shoal, stn DW4880 (MNHN). B. Protoconch of the same. C–F. Radula, Walters Shoal, stn DW4881 (MNHN). C. Entire width of radula. D. Central field and inner marginals. E. Detail of lateral and inner marginal teeth. F. Marginal teeth. Scale bars: A=500 μm; B, D–F =100 μm; C= 200 μm.