Emarginula salebrosa, Herbert, 2024

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 : 12-14

Emarginula salebrosa sp. nov.

urn:lsid:zoobank.org:act:CAA337F8-D068-4E4D-BECB-300A2A848FB8

Fig. 5

Diagnosis

Shell small and thick, uniformly whitish; apex strongly recurved, close to or just beyond posterior margin of base; anterior face slightly flattened either side of slit; anterior slit narrow and deep; sculpture coarsely cancellate, comprising 14–16 primary radial ribs with narrower secondary ribs in intervals; ribs with strong nodules where crossed by coarse concentric ridges; interstices between ribs and ridges simple, roundly quadrate depressions with single or paired intritacalx pits.

Etymology

From the Latin “ salebra, salebrosus ” – “roughness, rough”; in reference to the coarse sculpture.

Material examined

Holotype

WALTERS SHOAL • empty shell; slopes, stn DW4898; 33°09′ S, 44.01′ E; depth 652–668 m; 6 May 2017; MNHN-IM-2000-38262 .

Paratypes

WALTERS SHOAL – slopes • 2 empty shells; same collection data as for holotype; MNHN-2000-38263 • 5 empty shells; stn DW4881; 33°16′ S, 43°50′ E; depth 377–382 m; 2 May 2017; MNHN-2000-38264 • 6 empty shells; stn DW4883; 33°14′ S, 43°51′ E; depth 290–326 m; 2 May 2017; MNHN-2000-38265 • 8 empty shells; stn DW4892; 33°12′ S, 44°01′ E; depth 624–646 m; 4 May 2017; MNHN-2000-38266 • 6 empty shells; stn DW4899; 33°09′ S, 44°02′ E; depth 707–720 m; 6 May 2017; MNHN-2000-38267 • 4 empty shells; stn DW4900; 33°10′ S, 44°01′ E; depth 660–670 m; 6 May 2017; MNHN-2000-38268 .

Other material

WALTERS SHOAL – slopes • 1 empty shell; stn DW4880; 33°17′ S, 43°51′ E; depth 275–318 m; 1 May 2017; MNHN • 1 empty shell; stn DW4885; 33°17′ S, 43°55′ E; depth 272–380 m; 3 May 2017; MNHN • 1 empty shell; stn DW4888; 33°10′ S, 43°57′ E; depth 299–311 m; 3 May 2017; MNHN • 1 empty shell, juvenile; stn DW4890; 33°09′ S, 43°59′ E; depth 492–588 m; 4 May 2017; MNHN .

Description

SHELL. Small (basal length up to 8.4 mm) and thick; apex strongly recurved, extending slightly beyond posterior margin of base in some specimens, not quite reaching it in others; dorsal profile strongly convex, basal outline broadly ovate (L/W=1.3–1.4), flat or slightly concave in side view; height moderate (H/L 0.56–0.63); anterior slope humped in side view, anterior face slightly flattened either side of slit; posterior slope almost straight and steeply inclined in largest specimens, less so in smaller ones; protoconch tightly tucked beneath apex, missing in many specimens. Anterior slit narrow and moderately deep, approx. one-third of anterior slope; selenizone initially forming a low mid-line rib (margins scarcely raised) with coarse lunulae, but selenizone becoming proportionately less prominent with growth, its margins weaker than neighbouring primary ribs, but not sunken; remaining sculpture coarsely cancellate, comprising 14–16 primary radial ribs with narrower secondary ribs between them; occasional tertiary ribs laterally near basal margin; radial sculpture crossed by coarse concentric ridges, equal in strength to secondary ribs; radial ribs with strong nodules where crossed by concentric ridges; interstices between ribs and ridges simple, roundly quadrate depressions rather than crisp reticulations, with single or paired intritacalx pits; basal margin coarsely crenulated by ends of radial ribs; interior with broad, low thickened ridge underlying selenizone, interior of apex clearly visible.

PROTOCONCH ( Fig. 5F ). Somewhat eroded in material available, but typically emarginuliform; a single whorl sculptured with traces of irregular superficial granulation; a thickened terminal lip not evident; maximum diameter ± 140 μm.

COLOUR. Fresher juvenile specimens uniformly white, larger shells dirty white.

DIMENSIONS. Holotype, base 7.0× 5.4 mm, height 4.4 mm; largest specimen, base 8.4 ×6.0 mm, height 4.7 mm.

Distribution

Known only from the slopes of Walters Shoal, at depths of 311–707 m; living specimens unknown. The species may in fact be extinct (see below).

Remarks

The coarse sculpture of Emarginula salebrosa sp. nov. resembles that of E. nodulicostata sp. nov., but the present species attains a much larger size (basal length 8.4 mm vs <3.5 mm), has a less recurved apex and lives at significantly greater depths (> 300 m vs <50 m). Another sculpturally similar species is E. circumalbum Poppe & Tagaro, 2020 from the Philippines, but that species has a somewhat broader shell, finer radial ribs, a much shorter slit and the lunulae of the selenizone protrude well above the shell surface in side view. Emarginula dahli Thiele, 1913 from the Bismark Archipelago has a more strongly recurved apex and a keel-like selenizone with raised edges and protruding lunulae.

None of the available specimens of Emarginula salebrosa sp. nov. are in fresh condition. All, even the juvenile individuals, appear to be old and some are filled with consolidated sediment suggesting that they are subfossil. It is thus quite possible that the species is no longer extant.

Figures

Fig. 5. Emarginula salebrosa sp. nov. A–D. Holotype, base 7.0×5. 4 mm, height 4.4 mm (MNHM- IM-2000-38262). E. SEM of juvenile specimen showing detail of sculpture, stn DW4899, basal length 4.1 mm (paratype, MNHN-IM-2000-38267). F. Protoconch, stn DW4899, scale bar =100 μm (paratype, MNHN-IM-2000-38267).