Stomatella multilirata, 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 : 102-106

Stomatella multilirata sp. nov.

urn:lsid:zoobank.org:act:C53FAA23-F8D5-4AFC-853A-4C7CCD3D453E

Figs 38F , 41D–I , 42–43

Diagnosis

Shell depressed auriform, maximum dimension up to 11 mm; last adult whorl expanding very rapidly and aperture greatly enlarged; sculpture of numerous fine, close-set, spiral lirae, alternating in strength as intermediaries arise; axial sculpture of weak collabral growth-lines, stronger on last half-whorl rendering sculpture weakly and irregularly decussate; apex whitish, remaining shell predominantly crimson, sometimes with an orange tint, variously patterned with paler axial flames or whitish flecks and tent-like markings.

Etymology

From the Latin “ multus ” – “much or many” and “ lira, lirata ” – “a ridge, ridged”; in reference to the sculpture of many fine spiral ridges.

Material examined

Holotype

WALTERS SHOAL • living specimen; summit area, south-west, stn WS03; 33°12.2′ S, 43°50.8′ E; depth 40 m; 30 Apr. 2017; DNA tissue sample; MNHN-IM-2013-67246 .

Paratypes

WALTERS SHOAL • 1 living specimen; same collection data as for holotype; DNA tissue sample; MNHN-IM-2013-67245 • 1 living specimen; same collection data as for holotype; DNA tissue sample; MNHN-IM-2013-67293 • 1 living specimen; summit area, south-west, stn WR01; 33°12.2′ S, 43°50.8′ E; depth 36 m; 30 Apr. 2017; DNA tissue sample; MNHN-IM-2013-67244 • 12 specimens, some living; summit area, south, stn WB05; 33°15.1′ S, 43°54.5′ E; depth 26–30 m; 1 May 2017; radula SEM prep.; MNHN-IM-2000-35729 • 4 specimens, living; summit area, south-east, stn WS08; 33°13.7′ S, 43°55.9′ E; depth 30–33 m; 3 May 2017; MNHN-IM-2000-35730 • 1 living specimen; summit area, north-west, stn WB10; 33°09.1′ S, 43°51.8′ E; depth 30 m; 6 May 2017; DNA tissue sample; MNHN- IM-2013-67247 .

Other material

WALTERS SHOAL • 30 + specimens, some living; same collection data as for holotype; photographed alive; MNHN • 1 living specimen; summit area, south-west, stn WR02; 33°12.2′ S, 43°50.8′ E; depth 40 m; 30 Apr. 2017; MNHN • 30 + specimens, some living; summit area, south-west, stn WS04; 33°12.2′ S, 43°50.8′ E; depth 40 m; 30 Apr. 2017; MNHN • 50 + empty shells; summit area, south, stn WS06; 33°15.1′ S, 43°54.5′ E; depth 26 m; 1 May 2017; MNHN • 50 + empty shells; summit area, south, stn WS07; 33°15.4′ S, 43°52.2′ E; depth 30–33 m; 2 May 2017; MNHN • 30 + empty shells; summit area, south-east, stn WS08; 33°13.7′ S, 43°55.9′ E; depth 30–33 m; 3 May 2017; MNHN • 14 specimens, some living; summit area, north-west, stn WB09; 33°13.8′ S, 43°55.8′ E; depth 27–30 m; 4 May 2017; MNHN • 10 specimens, some living; summit area, north-west, stn WB10; 33°09.1′ S, 43°51.8′ E; depth 30 m; 6 May 2017; MNHN .

Description

SHELL. Small (maximum dimension up to 11 mm), thin, depressed-auriform; last adult whorl expanding very rapidly; spire small, but prominent, its whorls rounded with indented suture; periphery rounded, slightly below mid-whorl; base flattened, anomphalous; teleoconch of up to 3.0 whorls; aperture greatly enlarged, often distinctly arched relative to substratum. First teleoconch whorl with 3 spiral lirae, one at shoulder slightly larger, increasing to 4 by end of whorl; additional lirae arise by intercalation reaching ± 8 by end of second whorl; lirae remaining distinct and very numerous on final whorl ( Fig. 42B ), usually alternating in strength as intermediaries arise; axial sculpture of weak collabral growth-lines, often somewhat stronger on last half-whorl and rendering sculpture weakly and irregularly decussate; stronger growth scars common on last quarter-whorl; base with similar spiral sculpture, but lirae finer and less distinct toward columella. Aperture elongate, roundly rectangular; peristome complete or nearly so; columella strongly concave, curving smoothly into outer lip; outer lip thin; paries and upper columella somewhat thickened by nacreous callus; interior highly nacreous when fresh, underlying spiral sculpture evident by transparency.

PROTOCONCH ( Fig. 42D ). Translucent white; diameter 200–225 μm, ca 1.25 whorls, apical beak weak or absent; sculpture indistinct, most specimens somewhat worn, but traces of fine, widely spaced, spiral threads occasionally evident; terminal lip convex with low subterminal varix.

COLOUR. Apical 1.0–1.5 whorls usually whitish, occasionally translucent corneous with whitish axial bands; second whorl often with brown blotches, becoming progressively more pinkish-red; final whorl predominantly crimson, sometimes with an orange tint, variously patterned with paler axial flames or whitish flecks and tent-like markings; early part of final whorl commonly with pattern of fine alternating crimson and pinkish-brown spiral lines; this pattern congruent with spiral lirae and tending to exaggerate them; columella and inner base white, subperipheral interface between white and crimson zone distinct and frequently scalloped ( Fig. 41H ).

DIMENSIONS. Holotype, maximum dimension 8.3 mm; largest specimen, maximum dimension 11.0 mm.

OPERCULUM. Absent.

RADULA ( Fig. 43 ). Formula ∞+5+1+5+∞, with ± 30 evenly arcuate, transverse rows of teeth. Rachidian tooth with trigonal base, narrow frontal shaft element and reduced cusp, buttressed on each side by alate flange giving cusp hooded appearance. Lateral teeth with shafts and base-plates overlapping extensively, medial portion of each hidden behind its inner neighbour; cusps comprising larger central denticle with two smaller denticles on each side at cusp base; cusps progressively larger from first to fifth lateral, inner ones hastate, outer ones bluntly spathulate. Cusps of inner marginals elongate-spathulate with well-developed basal denticle on outer margin (another also present on inner margin, but usually hidden); shaft of innermost marginal with broad alate medial extension that interlocks with deep socket on outer edge of fifth lateral ( Fig 43C ); cusps of marginal teeth with progressively finer and more numerous denticles toward edge of radula ( Fig. 43D ); cusps of outermost marginals roundly spathulate with pectinate fringe.

EXTERNAL ANATOMY. Based on rehydrated specimens and one individual photographed alive ( Fig. 38F ): as described for Stomatellinae by Hickman & McLean (1990). Head-foot pale fawn-yellow, extensively mottled with darker shades of yellowish-orange. Cephalic lappets present, their margins shallowly scalloped; neck lobes well developed with margins entire; epipodium with three whitish epipodial tentacles on each side and small branched lobes that lie closely applied to ventral shell margin; sides of foot with numerous small tubercles; metapodium enlarged and extending well beyond posterior margin of shell.

Distribution

Known only from the summit area of Walters Shoal, at depths of 26–40 m (living); habitat dominated by encrusting coralline algae; collected by hand, and by brushing and suction sampling.

Remarks

I have already commented on the confused taxonomy of stomatelline trochids ( Herbert 2015: 61) and it is thus not without some reservation that I describe a new species while so many of those already proposed remain taxa inquirenda. Amongst stomatelline genera, the depressed, haliotiform shape and relatively fine sculpture of the present species clearly ally it with Stomatella , of which the only species currently recognised as occurring in the south-western Indian Ocean is Stomatella auricula Lamarck, 1816 ( Herbert 2015). That species differs from S. multilirata sp. nov. in attaining a larger size (diameter> 20 mm) and appearing smoother, the spiral sculpture comprising only fine incised spiral striae (rather than raised spiral lirae), separated by broad, flat-topped intervals (see above and Mermod & Binder 1963). Indeed, in many of the described species of Stomatella the sculpture is incised rather than raised, and those described as having a sculpture of raised lirae or threads have frequently proven to belong to Synaptocochlea Pilsbry, 1890 ( Trochidae : Fossarininae). The depressed, elongate shell and highly nacreous interior of the present species, together with its protoconch and radula morphology and lack of an operculum, clearly demonstrate that it is not referable to Synaptocochlea . Stomatella stellata Souverbie in Souverbie & Montrouzier, 1863 from New Caledonia is of similar size and sculpture, but the shell is more domed and much less elongate ( Herbert 1996). The radula of S. multilirata is similar to that of S. auricula , but the cusp of the rachidian in that species is considerably larger, almost the same size as that of the innermost lateral ( Hickman & McLean 1990: fig. 67c and pers. obs.).

Figures

Fig. 38. A–B. Calliostoma pantopunctatum sp. nov., holotype, living animal, shell diameter 5.8 mm (MNHN-IM-2013-67275). C–E. Kaiparathina monticola sp. nov., holotype, living animal, anterolateral structure arrowed, shell diameter 6.8 mm (MNHN-IM-2013-67168). F. Stomatella multilirata sp. nov., Walters Shoal, stn WS03, greatest shell dimension 6.0 mm (MNHN). Images courtesy of Alain Barrère/ MNHN.

Fig. 41. A–C. Stomatella auricula Lamarck, 1816, Walters Shoal, stn DW4887, maximum dimension 6.8 mm (MNHN). D–I. Stomatella multilirata sp. nov. D–F. Holotype, maximum dimension 8.3 mm (MNHN-IM-2013-67246). G–I. Paratype with more orange coloration and tented pattern of whitish markings, maximum dimension 9.5 mm (MNHN-IM-2000-35729).

Fig. 42. Stomatella multilirata sp. nov., paratypes, subadult (MNHN-IM-2000-35730). A–C. Detail of teleoconch sculpture. D. Protoconch morphology. Scale bars: A= 0.5 mm; B–C =200 μm; D =50 μm.

Fig. 43. Stomatella multilirata sp. nov., radula (paratype, MNHN-IM-2000-35729). A. Entire width of radula. B. Detail of rachidian and lateral teeth. C. Outer lateral and inner marginal transition zone. D. Outer marginal teeth. Scale bars: A=100 μm; B–C =50 μm; D = 10 μm.