Neilonella 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 : 110

Neilonella sp.

Fig. 7C, D .

Material.— Five specimens (including two figured: ZPAL V.48/12, 13), partial shells, from the upper Paleocene of Fossildalen , Spitsbergen, Svalbard .

Measurements.—L, 4.5–6.9 mm; H, 3.5–4.9 mm; W, 2.1– 3.0 mm; H/L, 0.71–0.80; W/L, 0.44–0.58; n = 5.

Description. —Shell small, moderately inflated, elongate-ovate, equivalve, nearly equilateral. Surface sculptured with fine commarginal ribs. Antero-dorsal margin broadly rounded, passing into semicircular anterior margin; posterodorsal margin nearly straight, sloping gently into bluntly pointed posterior end; ventral margin broadly arcuate. Escutcheon not demarcated but broad. Beak not very prominent, slightly opisthogyrate, located centrally. Hinge with two series of very small teeth. Pallial sinus narrow, shallow, posterior muscle scar subquadrate.

Remarks. —Although we could not determine the presence of a resilifer, the available specimens are considered to belong in Neilonella because of their elongate-ovate outline, the presence of many fine commarginal ribs on the shell surface and the bluntly pointed posterior end. They resemble Neilonella alleni Amano and Jenkins, 2017 , from the Selandian (middle Paleocene) Katsuhira Formation in eastern Hokkaido, Japan, in their small size and in having sculpture of fine commarginal ribs. However, the anteriorly situated and more bluntly pointed beak of N. alleni enables us to separate it from the present species.

Figures

Fig. 7. Non-chemosymbiotic protobranch bivalves from the upper Paleocene, Basilika Formation, Fossildalen (A–E, G, I–K) and Zachariassendalen (F, H), Spitsbergen,Svalbard.A.?Nucula sp., ZPAL V.48/10,internal mold of right valve.B.?Malletia sp., ZPAL V.48/11, right valve.C, D.Neilonella sp.C. ZPAL V.48/12, left valve sculptured by fine commarginal ribs. D. ZPAL V.48/13, partial shell, right valve (D1), dorsal view of both valves (D2). E–K. Yoldiella spitsbergensis Amano sp. nov. E. Holotype, ZPAL V.48/17, internal mold, right valve (E1), hinge part (E2). F. Paratype, NRM-PZ Mo 186241, silicified shell, hinge part (F1), outer surface (F2). G. Paratype, ZPAL V.48/18, internal mold, right valve (G1), hinge part (G2). H. Paratype, NRM-PZ Mo 186242, silicified shell, right valve. I. ZPAL V.48/19, internal mold, left valve. J. ZPAL V.48/20, partial shell, left valve. K. ZPAL V.48/21, partial shell, partly preserved outer surface, left valve.