Marginella seguenzai, Perna & Vazzana, 2016

Perna, Rafael La & Vazzana, Angelo, 2016, On the last occurrence of Marginella Lamarck, 1799 (Gastropoda, Marginellidae) in the Mediterranean: description of a new species from the Early Pleistocene and paleoceanographic implications, Geodiversitas 38 (3), pp. 451-461 : 455-458

Marginella seguenzai n. sp.

( Figs 2 ; 5 A-L; 6A, B)

TYPE MATERIAL. — Holotype and five paratypes . Holotype:H 9.3 mm, D 5.3 mm ( MZB 60202) . — Paratypes: Paratype 1, H 10.6 mm, D 5.9 mm ( MZB 60203) ; Paratype 2, H 9.7 mm, D 5.4 mm ( MZB 60203) ; Paratype 3, H 9.0, D 5.3 mm ( MZB 60203) ; Paratype 4, H 8.4 mm, D 4.8 mm ( MBMPRC) . Paratype 5, H 11.8 mm, D 6.7 mm ( MBMPRC) .

ETYMOLOGY. — After Giuseppe Seguenza (Messina 1833-1889), eminent Italian geologist and paleontologist.

MATERIAL EXAMINED. — Over 80 shells, all from the type horizon ( MBMPRC).

TYPE HORIZON. — Bed b in the outcrop of Gallina, Reggio Calabria ( Fig. 1C ).

TYPE LOCALITY. — Gallina, Reggio Calabria, Calabrian, Early Pleistocene.

DIAGNOSIS. — A small Marginella species , biconical, moderately inflated, with last whorl making about 85% of shell height, maximum diameter at shell mid-height. Apex blunt, spire low, with two flat whorls. Aperture narrow, elongate, somewhat parallel-sided, with four columellar plications. Outer lip internally smooth, thickened by a wide outer rim.

DISTRIBUTION. — The new species is only known from the type locality.

Because of the allochthonous character of the fauna from Gallina , M. seguenzai n. sp. could be a bathyal species, or a shelf species whose shells were transported to bathyal depths. Marginella mainly has a shallow water distribution, but some species are widely dis-

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tributed bathymetrically (e.g. Goud & Neefs 1996), while few are only known from bathyal depths (e.g. Coomans 1975; Bouchet & Warén 1985). Considering the general good preservation of shells and the prevalent composition of the molluscan assemblage, it can be assumed that M. seguenzai n. sp was a deep water species. This hypothesis is also supported by close similarities occurring between the new species and a Recent deep water species from the NE Atlantic, as discussed in Distribution part.

DESCRIPTION

Shell small, up to c. 12 mm in height, moderately solid, biconical, with last whorl making about 85% of total height; maximum diameter at about mid-height to slightly posterior; apex blunt. Protoconch not well distinct from teleoconch, smooth, formed by about one whorl. Spire low, consisting of about two flat-sided whorls. Sutures shallow, poorly impressed, distinct. Sometimes, the spire is slightly narrower, forming a stepped suture with last whorl. Last whorl regularly rounded, gently tapering anteriorly, rarely forming a poorly distinct basal constriction. Aperture elongate, narrow, somewhat parallel-sided, taking about 70% of shell height. Outer lip internally smooth; externally bordered by a well distinct, wide rim, making the lip uniformly thick; straight for most of its length, posteriorly arched; anterior notch shallow, moderately wide. Four columellar plications, all well distinct, not markedly prominent, the posterior one smaller. Sometimes a fifth false plication is present, as an elongate, weak tubercle or as a thin plait similar to a true plication. Columellar and parietal callus rather wide, forming a thin glossy lining near aperture, slightly thicker posteriorly.

REMARKS

The genus Marginella typically includes species with brightly coloured shells, with a range of patterns (variously combined bands, flames, lineoles, blotches, dots, etc.) ( Goud & Neefs 1996; Cossignani 2006), but several colourless species are also known, mainly from deep waters ( Bouchet & Warén 1985; Goud& Neefs 1996). No preserved colour pattern was observed in the material of M. seguenzai n. sp., either under daily light, or under UV light, but the uniform milky aspect of the shell surface suggests a colourless, or lightly coloured, original condition.

In addition to the variability in size and shape, another variable character was observed: some shells (about 20%) show a “false fifth plication” ( Coovert & Coovert, 1995). In most cases it consists of a weak, elongate tubercle near the fourth (posterior) plication ( Fig.6A ). Rarely, the false plication is more elongate and stronger, resembling a true, internally continuous, columellar plication (( Fig. 6B ).

In some cases, the transition between spire and last whorl appears somewhat stepped, the spire being slightly narrower than the adjacent last whorl, as seen in Figure 5H, I .

None of the Marginella species known from the Pliocene of Estepona ( Muñiz Solis 2002; Landau et al. 2006a) is particularly similar to the new species, all markedly differing in some respects (mainly size, shape and robustness).

Few of the many species known from Eastern Atlantic, deserve a comparison with the new species, such as Marginella gloriosa Jousseaume, 1884 , M. marocana Locard, 1897 , M. bavay Dautzenberg, 1910 , M. aronnax Bouchet & Warén, 1985 , M. colomborum ( Bozzetti, 1995) and M. gilva Goud & Neefs, 1996 , but in most cases there are evident differences involving size and shape (convexity of spire whorls, spire elevation, shell slenderness, shape of outer lip, etc.). Of these species, only M.colomborum shows an interesting overlap of characters with the new species. It was described from the Josephine Bank ( Bozzetti 1995), a seamount in the North-East Atlantic, off Cape St. Vincent ( Gubbay 2003). Though originally assigned to the genus Prunum , this species must be allocated in the genus Marginella . The species was examined on three shells from the type locality ( Fig. 7 A-D): the shell is colourless (actually very light pinkish, with the outer lip white), height close to that of M. seguenzai n. sp. also in the range (12.9- 11.3 mm in the original description, 10.0- 8.8 mm in the examined material), outer lip moderately thick, making a broad curve posteriorly, as in the new species. A remarkable difference from M. seguenzai n. sp. is the last whorl convexity, being M. colomborum more inflated(H/D 1.70-1.86 in the examined material) than the new species, apparently without overlap.The shape of the aperture, rather parallel-sided in the new species and widening anteriorly in M. colomborum , is another outstanding difference. Moreover, M. colomborum has slightly convex spire whorls, whereas they are flat in the new species.

Marginella colomborum has been also recorded from Seine and Ampère, other NE Atlantic seamounts ( Beck et al. 2005). On WoRMS, Gofas (2015) added: “Endemic of Josephine, Seine and Ampère seamounts; common on Josephine, 270-335 m, rare on Seine and Ampère; a very similar if not identical species is found in the Italian Pleistocene”. The fossil species to which Gofas refers is M. seguenzai n. sp., of which he had examined some shells. Gofas’ view about the close similarity between M. colomborum and the fossil species is confirmed, but they are evidently distinct species.

Figures

FIG. 2. — Sample of 36 shells used for morphometry and shape analysis, with identification number. Scale bar: 5 mm.

FIG. 5. — Marginella seguenzai n. sp.: A-C, holotype, H 9.3 mm (MZB60202); D, paratype 1, H 10.6 mm (MZB60203); E-G, paratype 2, H 9.7 mm (MZB60203); H, I, paratype 3, H 9.0 mm (MZB60203); J, paratype 4, H 8.4 mm (MBMPRC); L, paratype 5, H 11.8 mm (MBMPRC). Scale bar: 5 mm.

FIG. 1. — A, Map of the Messina Strait;B, location of the outcrop;C, schematic stratigraphy of the outcrop (asterisk indicates the sampled bed).Abbreviations:see text.

FIG. 6. — Marginella seguenzai n. sp.: shells with a fifth false plication (arrows): A, poorly developed fifth plication; B, well developed fifth plication. Scale bar: 2 mm.

FIG. 7. — Marginella colomborum (Bozzetti,1995),Josephine Bank,Seamount 1 Exp.,St.DW37,255-270 m,36°42N,14°18W,4 Oct.1988 (MNHN):A-C, H 10.0 mm; D, H 9.8 mm. Scale bar: 5 mm.