Imbricoscelis, 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 : 31-32

Genus Imbricoscelis gen. nov.

urn:lsid:zoobank.org:act:F5D489A2-3CBD-4ACB-97E1-B0B7BECE60A8

Type species

Brookula coronis Barnard, 1963 .

Diagnosis

Shell small, globose-turbiniform; whorls evenly rounded; apical sculpture of collabral ribs, developing into broad forwardly sloping lamellae on later whorls, frequently overlapping; microsculpture of slash-like marks; base rounded and umbilicate; exterior of outer lip with a strong subterminal varix. Radula formula ∞+3+1+3+∞, rachidian weakly hooded; teeth in central field with complex interlocking of tooth bases and shafts, their cusps coarsely dentate; latero-marginal plate absent; marginal teeth slender with pectinate outer margin. Operculum corneous, broadly multispiral.

Etymology

From the Latin “ imbrex ” – “a roofing-tile”, “ imbricatus ” – “overlapping” and the Greek “ skelis ” (σκελίς) – “a rib”; with reference to the close-set, overlapping, lamellate axial sculpture. Gender feminine.

Remarks

Many features of the shell, including the microsculpture and protoconch form, as well as the radula and operculum indicate that Imbricoscelis gen. nov. has affinity with chilodontaid and calliotropid seguenzioids, but it is unlike any of the existing genera known therein. The type species was originally referred to Brookula Iredale, 1912 (unassigned Seguenzioidea ), but it shows only limited similarity to the type species Brookula stibarochila Iredale, 1912 , a minute, shallow-water, subtropical species which has coarsely cancellate spire whorls (topotype illustrated by Warén 1992). Species of the deeper-water genera Benthobrookula Clarke, 1961 and Vetulonia Dall, 1913 are perhaps more similar, but they have far fewer axial ribs, much more distinct spiral sculpture and lack a strong collabral varix behind the outer lip. The recently described genus Toroidia Hoffman & Freiwald, 2018 from the NE Atlantic likewise has lamellate axial ribs, but they are much narrower than those of Imbricoscelis and do not overlap. In addition, the shells are more elevated, have a narrower umbilicus, a more globose protoconch and the outer lip lacks a subterminal varix ( Hoffman & Freiwald 2018).

The form of the protoconch and the morphology of the radula, in particular the relatively coarsely dentate teeth in the central field and the lack of any latero-marginal structures, leads me to believe that Imbricoscelis gen. nov. has more affinity with the Chilodontaidae than with the Calliotropidae . The protoconch is neither bulbous nor strongly exsert as it is in many extant calliotropids (compare Figs 14B and 16B ).

Figures

Fig. 14. A–B. Calliotropis velata Vilvens, 2006, Walters Shoal, stn CP4911 (MNHN), scale bars =200 μm. A. Microsculpture, third whorl. B. Protoconch. C. Danilia textilis Herbert, 2012, Walters Shoal, stn DW4887, height 11.7 mm (MNHN-IM-2013-67256). D–E. Vaceuchelus gemmula (Turton, 1932), Walters Shoal, stnWB05, height 3.4 mm (MNHN-IM-2013-67254).F–H. Vetulonia parajeffreysi Absalão & Pimenta, 2005, Walters Shoal, stn CP4913, diameter 2.5 mm (MNHN). I. Vetulonia parajeffreysi, protoconch, Walters Shoal, stn CP4913, scale bar =100 μm (MNHN).

Fig. 16. Imbricoscelis coronis (Barnard, 1963) gen. et comb. nov., SEM, Walters Shoal, stn CP4902 (MNHN). A. shell apex. B. Protoconch. C. Sculpture of overlapping lamellate ribs with fine spiral lirae. D. Microsculpture of slash-like axial marks.E. Microsculpture overlain by intritacalx layer.F. Operculum. G–I. Radula. G. Full width of radula. H. Rachidian and lateral teeth in central field. I. Latero-marginal area. Scale bars: A, F =500 μm; B, E=100 μm; C–D =200 μm; G= 25 μm; H–I =20 μm.