Caspiconcha rubani, Kiel & Campbell & Gaillard, 2010

Kiel, Steffen, Campbell, Kathleen A. & Gaillard, Christian, 2010, New and little known mollusks from ancient chemosynthetic environments, Zootaxa 2390 (1), pp. 26-48 : 37-38

Caspiconcha rubani sp. nov.

( Fig 7 )

Diagnosis: Typical Caspiconcha species with straight dorsal and ventral margins; strong internal ridge and groove; strong, elongate ligament, elongate, dorsally located anterior adductor muscle scar bordered by strong ridge on posterior side.

Holotype: USNM 535868 , L = 61 mm.

Paratypes: USNM 535869 , L = 40 mm ; USNM 538736 , L = 86 mm ; USNM 538737 , L = 80 mm ; USNM 538738 , L = 70 mm ; USNM 538739 , L = 87 mm .

Type locality and strata: The early Cretaceous (Hauterivian) Peregrinella -limestone in the Planerskoje section, southeastern Crimea, Ukraine (35°12’E 44°585’N), described by Kiel and Peckmann (2008) .

Material: 30 specimens from the type locality.

Description: Large, elongate-oval modioliform shell; umbo anterior; posterodorsal margin long, straight, transition to posterior margin at distinct angle, maximum curvature of posterior margin near ventral margin; ventral margin straight. Ligament external, long, thick; fine commarginal sculpture on external shell surface. Strong and straight internal ridge with parallel groove from umbo to posteroventral end of posterior adductor muscle scar; anterior adductor muscle scar deep, oval with somewhat pointed dorsal corner, bordered posteriorly by strong ridge and prominent myophoric ridge below; posterior adductor muscle scar elongate, rather indistinct; pallial line entire, with fine, oblique ribblets radiating inward on anterior part of shell.

Remarks: Caspiconcha rubani n. sp. differs from the type species C. withami by its stronger internal ridge and its more dorsally located and more roundish anterior adductor muscle scar. Kiel and Peckmann (2008) discussed three additional Late Jurassic to Cretaceous seep-restricted species, which are best placed in Caspiconcha . Among these, the Californian C. major Gabb, 1869 , can easily be distinguished from C. rubani because it lacks the internal ridge. Stewart (1930) noted that Myoconcha americana Stanton, 1895 , from the Albian seep deposit at Cold Fork of Cottonwood Creek is a juvenile of C. major , and synonymized the two species. This agrees with observations of the senior author of this paper. Also the Czech Myoconcha aff. transatlantica from the Hauterivian Peregrinella -limestones at Koniakauer Schloss lacks the internal ridge ( Ascher 1906). The large ‘ Calyptogena sp. ’ described by Hikida et al. (2003) from the late Cretaceous Omagari seep site in northern Hokkaido most probably also belongs to Caspiconcha (cf. Amano and Kiel 2007; Kiel and Peckmann 2008).

Distribution: Type locality only.

Etymology: For Dmitry Ruban, Rostov on Don, for making the senior author aware of the Crimean seep site where this species was discovered.

Figures

FIGURE 7. Caspiconcha rubani n. sp. from a Hauterivian (Early Cretaceous) seep carbonate in the Planerskoje section, Crimea, Ukraine. A. Holotype (USNM 535868), arrows indicates the anterior and posterior adductor scars. B. Paratype (USNM 538736) showing internal ridge and ligament. C. Paratype (USNM 535869), specimen with preserved shell material. D. Paratype (USNM 538737), articulate specimen, arrow indicates the strong external ligament. E. Paratype (USNM 538738), arrow indicates the well-developed anterior adductor scar. F, G. Paratype (USNM 538739), arrows indicate the course of the pallial line; close-up (G) shows the irregular dorsal margin of the pallial line.