Emarginula icosisculpta, Simone, Luiz Ricardo L. & Cunha, Carlo M., 2014

Simone, Luiz Ricardo L. & Cunha, Carlo M., 2014, Taxonomical study on the mollusks collected in Marion-Dufresne (MD 55) and other expeditions to SE Brazil: the Fissurellidae (Mollusca, Vetigastropoda), Zootaxa 3835 (4), pp. 437-468 : 455-456

Emarginula icosisculpta , new species

Figures 135–139

Types. Holotype MNHN 25323. Paratype: MZSP 102949, 1 shell from type locality.

Type locality. Brazil. Espírito Santo; Ilha de Trindade, Enseada dos Portugueses, 20°30’15”S 29°18’46”W, 10–12 m (MD55 sta. 1; Bouchet col., v/1987).

Diagnosis. Apex pointed, posterior located, turned posteriorly. Height 32% of length. Sculptured by ca. 20 strong radial cords, with interspaces regularly filled by commarginal sculpture as transverse scales.

Description. Shell size ca.2.5 mm; low, limpet-like; height ca.32% of length. White, opaque. Protoconch of 1.5 rounded whorls (Fig. 139); somewhat protruding, located laterally, situated on right in posterior edge of apex (Figs 136, 139); smooth, glossy; ca. 4% of total shell size. Slit anterior, rectangular, width 16% of length; 7% of shell width, 27% of shell length; edges rather irregular (Figs 135, 137, 138). Profile highly curved ventrally, sagittal profile in arc with imaginary center located ca. 50% of shell length ventral to highest shell region (Figs 136, 139). Sculpture of strong radial cords (Figs 135, 138), ca. 20 surrounding apex; gradually increasing in strength towards aperture; interspaces half of cords’ width, filled by comarginal sculpture as transverse scales; interval between comarginal sculpture ca. 1/2 of thread’s width, ca. 20 scales along median threads. Selenizone median, marked by narrow, elevated edges (elevation equivalent to that of cords); filled by somewhat regularly distributed lunules (Figs 135, 138). Aperture slightly concave, outline elliptical, width ca.60% of length; edges undulating due to radial cords. Inner surface smooth, simple, glossy (Fig. 137).

Measurements (in mm). Holotype: 2.5 by 0.8; paratype MZSP 102949: 2.2 by 0.8.

Distribution. Only known from type locality.

Habitat. 10–12 m depth (no indication about substrate; dead specimens).

Material examined: Types.

Etymology. The specific epithet is derived from the Greek eikosi (or icosi), meaning twenty, and sculpta, meaning sculpture, an allusion to the outer surface of shell sculptured by about 20 radial threads.

Remarks. Emarginula suspira is similar to a set of species occurring in north Atlantic and Eastern Pacific deepwaters such as Emarginula tuberculosa Libassi, 1859 ( Farfante 1947) , Emarginula angusta and E. dictya (both McLean, 1970: Figs 14–17). It differs in having a lower shell with a higher number and more closely spaced radial ribs. Emarginula suspira differs from E. tuberculosa (sensu Farfante 1947) mainly in having a low posterior beak, placed close to the apertural plane (Figs 94, 97); additionally, E. suspira has a stronger sculpture, which produces elevated nodes at the intersection of the concentric and radial ribs; the shell apex is low at the posterior margin of the shell, while it protrudes posteriorly in E. tuberculata . Emarginula suspira differ from E. sicula Gray, 1825 , from the Mediterranean and from E. crassa Sowerby, 1812 from the north Atlantic, by the stronger sculpture and by the wider and longer slit. The beak close to the ventral plane of the aperture also distinguishes E. suspira from E. phrixodes Dall, 1927 from the north Atlantic.

Emarginula suspira has been previously misidentified as Emarginula tuberculosa (see synonymy above). This species was described for Miocene fossils from Altavilla and Ficarazzi, Palermo, Italy ( Libassi 1859). This fact has not been noted by earlier authors (e.g., Farfante 1947; Leal 1991; Rios 2009), indicating a Miocene fossil from Mediterranean living presently along the coast of the Western Atlantic; this remarkable temporal and geographical distribution has not been discussed. On the other hand, the broad geographic range and the regional variation of the specimens have been interpreted as indicative of multiple species ( Leal 1991: 41). The Emarginula sp. 2 by Leal (1991: 42), from Atol das Rocas and Fernando de Noronha, may also refer to E. suspira .

Emarginula suspira varies considerably as discussed above (Figs 93–99). Larger specimens tend to be more rounded at the edge (Fig. 93), while the younger specimens tend to have more triangular outline in dorsal view (Figs 90, 96). The smaller specimens have a more widely spaced sculpture; elongated transverse pits can be seen in the concavity formed by reticulated sculpture (Fig. 99) produced only by the periostracum. The flattened posterior shell lip, with the beak approaching it, is one of the main characters of E. suspira , distinguishing it from the E. tuberculosa group. The posterior end of the aperture is generally convex (Fig. 95), but in rare specimens it can be concave (Fig. 98).

Emarginula icosisculpta cannot be confused with any other Atlantic species. Its well-curved low profile and the posteriorly positioned beak are unique characters. The strong radial sculpture, possessing few cords, is an additional distinctive character.