Akritogyra crenulata, 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 : 51-53

Akritogyra crenulata sp. nov.

urn:lsid:zoobank.org:act:8D95E498-B092-4E51-B2D9-86170462B027

Fig. 23

Diagnosis

Shell very small, turbiniform, slightly wider than high, whorls evenly rounded, base umbilicate; subsutural region crenulated by short, broad riblets; intervals between riblets with close-set, microscopic spiral threads; riblets much weaker peripherally; microsculpture comprising numerous close-set microscopic axial threads; riblets reappear on base crenulating umbilical margin; peristome complete, circular, slightly disjunct; interior non-nacreous.

Etymology

From the Latin “ crena, crenatus ” – “a notch, notched”, dim. “ crenula, crenulatus ”; with reference to the subsutural sculpture.

Material examined

Holotype

WALTERS SHOAL • empty shell; slopes, stn DW4886; 33°17′ S, 43°56′ E; depth 573–582 m; 3 May 2017; MNHN-IM-2000-38217 .

Paratypes

WALTERS SHOAL • 4 empty shells; same collection data as for holotype; MNHN-IM - 2000-38218 .

Description

SHELL. Minute (diameter up to 1.1 mm), turbiniform, slightly wider than high (H/D =0.81–0.93) whorls evenly rounded; periphery at mid-whorl; base umbilicate; teleoconch of up to 2.25 whorls. Early sculpture of short, broad riblets which crenulate subsutural region; intervals between riblets with close-set, microscopic spiral threads ( Fig. 23E ); riblets weaken considerably in peripheral region, but reappear on base crenulating umbilical margin; peripheral region rendered weakly undulant by remaining traces of axial riblets, but also with numerous close-set microscopic axial threads ( Fig. 23F ); latter quarter of last adult whorl usually lacking axial riblets below suture; umbilicus of moderate width, its rim rounded and crenulate, its interior with traces of low spiral lirae. Aperture circular, weakly prosocline, peristome complete and a little disjunct from penultimate whorl; outer lip simple; interior smooth, lacking obvious nacre.

PROTOCONCH ( Fig. 23G ). Globose, moderately exsert, comprising approx. 1.25 whorls, diameter ± 245 μm; with fine superficial granulation where unworn; terminal lip convex, not thickened.

COLOUR. Uniformly translucent milky-white.

DIMENSIONS. Holotype, height 0.85 mm, diameter 1.05 mm; largest specimen, height 1.03 mm, diameter 1.13 mm.

Distribution

Known only from the slopes of Walters Shoal, at a depth of 573–582 m; dredged on coarse sandy substrata; living specimens unknown.

Remarks

I refer this unusual species to Akritogyra simply because it shows some similarity to A. helicella Warén, 1993 from Iceland (Warén 1993). Quite possibly, this similarity is merely superficial, but I know of no other genus to which the species might belong, and choose to place it in Akritogyra rather than create a new genus based on shell characters alone. Akritogyra helicella has similar subsutural crenulation and microscopic, wrinkle-like axial microsculpture, but the shell is much more depressed and the umbilicus is wider. Warén (1993) likewise expressed reservations regarding his referral of A. helicella to Akritogyra , but opted for a conservative approach given the plethora of generic names available for skeneimorph gastropods.

Figures

Fig. 23.Akritogyra crenulata sp. nov. A–B.Apertural and oblique basal views of holotype, height 0.85 mm (MNHN-IM-2000-38217). C. Apical view, diameter 0.95 mm (paratype, MNHN-IM-2000-38218). D. Strongly sculptured specimen, height 0.93 mm (paratype, MNHN-IM-2000-38218). E. Detail of subsutural sculpture, scale bar = 100 μm (paratype, MNHN-IM-2000-38218). F. Microsculpture of holotype, scale bar = 50 μm. G. Protoconch of C, scale bar =100 μm.