Solemya sp.

Hryniewicz, Krzysztof, Amano, Kazutaka, Bitner, Maria Aleksandra, Hagström, Jonas, Kiel, Steffen, Klompmaker, Adiël A., Mörs, Thomas, Robins, Cristina M. & Kaim, Andrzej, 2019, A late Paleocene fauna from shallow-water chemosynthesis-based ecosystems, Spitsbergen, Svalbard, Acta Palaeontologica Polonica 64 (1), pp. 101-141 : 109

Solemya sp.

Fig. 6 .

Material.— Two specimens ( NRM-PZ Mo 183945, 183946), internal mold with shell partially adhering ( NRM-PZ Mo 183945) and butterflied internal mold ( NRM-PZ Mo 183946), from the upper Paleocene of Zachariassendalen , Spitsbergen, Svalbard .

Measurements.—NRM-PZ Mo 183945: L, 14.5 mm; H, 6.9 mm; W, 4.4 mm.

Description.—Shell small, thin, very inequilateral, with anterior constituting ca. 75% of length of shell. Umbones nearly undiscernible, dorsal margin straight, passing into slightly oblique and convex anterodorsal margin. Anterior margin rounded, with deepest point above median line. Anteroventral margin convex and oblique, ventral margin very weakly convex. Posterior margin rounded, posterodorsal margin incurved. Posterior adductor muscle scar demarcated anteriorly by ridge. Anterior adductor muscle scar connected with dorsal margin by elongate band. External ornament of ridges radiating from umbo; ridges much broader than their interspaces. Anterior half of shell bearing 12 ridges; total number of ridges unknown due to lack of complete shells. Soft periostracal flange extending a few millimetres beyond margin of the shell.

Remarks.—We have included the present species in Solemya Lamarck, 1818 , due to the presence of a faint ridge in front of the posterior adductor muscle scar. Such a ridge is present in some subgenera of Solemya , such as Austrosolemya Taylor, Glover, and Williams, 2008 , Petrasma Dall, 1908 , Solemyarina Iredale, 1931 , and Zesolemya Iredale, 1939 . The present species has no internal ligament demipads in front of the umbo that we could identify inequivocally, and so is reminiscent of Petrasma Dall, 1908 , but the small number of specimens does not allow us to check whether this is a constant feature. Therefore, we did not assign our species in a subgenus of Solemya .

The conchological features used to subdivide extant species of Solemya are mostly those of the posterodorsal and dorsal shell margin, such as the shape and length of the chondrophore and ligament, shape of the posterior adductor muscle scar and the shape of the anterior ligament extensions ( Taylor et al. 2008; Kamenev 2009). These features are not preserved in the material herein, so that identification to the species-level is not possible at present. External conchological characters, perhaps except for the relative position of the umbo in relation to the shell length, are not of great taxonomic significance for solemyids when internal shell features are absent (e.g., Amano and Ando 2011; Hryniewicz et al. 2014) and they should not be used by themselves for species discrimination.

Figures

Fig. 6. Solemyid bivalve Solemya sp. from the upper Paleocene, Basilika Formation, Zachariassendalen, Spitsbergen, Svalbard. A. NRM-PZ Mo 183945, shell (LV), internal mold (RV), left (A1) and right (A2) valve, dorsal view of both valves (A3), ventral view (A4). B. NRM-PZ Mo 183946, internal mold, butterflied specimen in dorsal view (LV, left valve; RV, right valve).