Cerastus praeinsularis, Neubert & Damme, 2012

Neubert, Eike & Damme, Dirk van, 2012, Palaeogene continental molluscs of Oman, Contributions to Natural History 20, pp. 1-28 : 18-19

Cerastus praeinsularis sp. nov.

( Figs. 18–19 )

Type specimens: Holotype NMBE 5018986 , paratype NMBE 5019050 .

Type locality: Wadi Darbat , Dhofar, Oman .

Stratum typicum: Paludal biomicritic limestones of the Zalumah Formation.

Age: Late Priabonian.

Material: This species is only represented by the holotype specimen.

Etymology: praeinsularis to pinpoint the early presence of this species in the area, which later gave rise to the Soqotra Archipelago, Yemen.

Diagnosis: Species characterised by the large periomphalum.

Description: Shell elongate turreted, with regularly increasing whorls (protoconch and first teleoconch whorl not preserved); upper teleoconch whorls covered by a fine axial sculpture of ribs; aperture broadly oval, columellar part triangular, partly covering the umbilicus; umbilicus broadly open, with a large periomphalum, delimited by a blunt crest (see arrows in Fig. 18b ).

Measurements: Holotype ( Fig. 18a ): H = 11.81 mm; Wh> 5.

Remarks: For the familial and generic affiliation, the same rationale is used as in C. pseudoena sp. nov. However, the peculiar form of the umbilicus of C. praeinsularis sp. nov. clearly differs from that of its fossil congener, but is quite similar to species from the Soqotran cerastid radiation. In this respect, it particularly resembles shells of the Modern endemic Soqotran genera Achatinelloides NEVILL, 1878 , and Passamaella PFEIFFER, 1877 ( Neubert 2005a, 2005b). This is here shown by a comparison with Achatinelloides hadibuensis (GODWIN-AUSTEN, 1881) ( Fig. 20 ), which shows a very similar umbilicus formation with a large periomphalum delimited by a blunt crest (see arrow in Fig. 20 ).

In our material, we also found a small shell consisting of a small protoconch and almost four teleoconch whorls, which are also covered by a dense pattern of axial ribs ( Fig. 19 ). The imperfect formation of the aperture makes it very probable that this is a juvenile shell. Superimposing this fossil with the holotype of C. praeinsularis sp. nov. reveals that the diameter and growing increment of both shells match almost perfectly. For this reason we interpret this shell as a juvenile of C. praeinsularis sp. nov. (NMBE 5019050).

Figures

Figs. 18–20: Species of Cerastidae. Fig. 18a: Cerastus praeinsularis sp. nov., Wadi Darbat, holotype NMBE 5018986 in frontal view. Fig. 18b: ditto, detail of last teleoconch whorls with the periomphalum. Fig. 19: C. praeinsularis sp. nov., only upper whorls preserved, Wadi Darbat, paratype NMBE 5019050. Fig. 20: Achatinelloides hadibuensis, Yemen, Soqotra Isl., Wadi Ayhaft, leg. K. van Damme. Details not to scale.