Musculus 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 : 113

? Musculus sp.

Fig. 9 .

1970? Arca sp. ; Anderson 1970: 92, pl. 9: 4a–b.

2016 Arcidae sp.; Hryniewicz et al. 2016: table 2.

Material.— Two specimens, including one fragmentary right valve ( NRM-PZ Mo 183957) from the upper Paleocene of Zachariassendalen , Spitsbergen, Svalbard and one ( GPIBo 153 ) from the upper Paleocene , locality 500 m west of Trigonometric point 25, Spitsbergen, Svalbard .

Description.—Shell small, with fine radial ornament separated by broad interspaces and superimposed on strong commarginal growth lines. Posterior end rounded, posterior lobe inclined ventrally. Details of anterior margin and inner shell surface unknown.

Remarks.—This radially ornamented mytilid was previously figured by Anderson (1970) and misidentified as an arcid, an identification followed by Hryniewicz et al. (2016). Closer examination of the material, supplemented by an additional specimen found during the field season in 2017 in Zachariassendalen, revealed that this species is actually a mytilid. Radial ornament superimposed on commarginal growth lines occurs among several mytilid genera. Radial ribs superimposed on strong commarginal growth lines and fading close to the ventral margin of the mid-shell section, and a median keel visible on the posterior lobe suggest that this species possibly belongs to Musculus Röding, 1798 , but the lack of well-preserved specimens makes our assignment tentative. From the ribbed mytilids described from the Paleocene strata of Nuusquaq, northwest Greenland Petersen and Vedelsby 2000), Brachidontes sp. 1 and Brachidontes sp. 2 have coarser radial ornament, whereas Brachidontes sp. 3 has somewhat similar ornament and a medial keel to those of the current species. Unfortunately, the fragmentary nature of our material does not allow for a more thorough comparison.

Figures

Fig. 9. Mytilid bivalve?Musculus sp. from the upper Paleocene, Basilika Formation,Zachariassendalen,Spitsbergen,Svalbard.NRM-PZMo 183957, shell, partially preserved left valve.