Trochozonites arabica, Neubert & Damme, 2012

Neubert, Eike & Damme, Dirk van, 2012, Palaeogene continental molluscs of Oman, Contributions to Natural History 20, pp. 1-28 : 20-22

Trochozonites arabica sp. nov.

( Fig. 25 )

Type specimens: Holotype NMBE 5018988 . 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: arabica for its presence on the Arabian Peninsula.

Diagnosis: Broad conical shell with strong opisthocline ribs.

Description: Shell broad conical; protoconch blunt, consisting of ca. 2 whorls without any obvious sculpture; last teleoconch whorl rapidly increasing, with a sharp peripheral keel; whorls only slightly rounded, suture simple and shallow; teleoconch whorls covered by strong opisthocline ribs; lower part of the shell (below the periphery) smooth; aperture depressed oval, peristome (probably) simple, sharp; form of umbilicus not clearly discernible, however, it seems to be quite narrow.

Measurements: Holotype ( Fig. 25 ): H = 5.04 mm; W = 5.27 mm; Wh> 5.

Remarks: The specific opisthocline ribs discriminate this shell from all cerastid shells, which have orthocline ribs. The shell form immediately recalls the shells of the afrotropical helicarionid genus Trochozonites PFEFFER, 1883 . To facilitate comparison, the figure of Trochozonites plumaticostata PILSBRY, 1919 from the Congo Basin is here provided ( Fig. 26 ). In his diagnosis of the species, Pilsbry (1919: 251) explicitly describes the "oblique, rather widely spaced, retractive, undulating riblets", which is close to what can be seen in T. arabica sp. nov. Nonetheless, the affiliation to such a badly understood genus remains with some doubts, because important character sets like the protoconch sculpture and microrelief are not preserved.

Figures

Figs. 25–26: Species of Helicarionidae. Fig. 25: Trochozonites arabica sp. nov., Wadi Darbat, holotype NMBE 5018988 in frontal, apical and lateral view. Fig. 26: Trochozonites plumaticostata, Ituri Forest, Penge (from Pilsbry 1919).