Nucinella nakremi Foster & Danise & Twitchett 2017, sp. nov.

• Main Authors: Foster, William J., Danise, Silvia, Twitchett, Richard J.
• Format: Other/Unknown Material
• Language: unknown
• Published: Zenodo 2016
• Subjects: Biodiversity; Taxonomy; Animalia; Mollusca; Bivalvia; Solemyida; Nucinellidae; Nucinella; Nucinella nakremi; Svalbard
• Online Access: https://doi.org/10.5281/zenodo.10883096; http://treatment.plazi.org/id/C53B0B4D8057E8236C4DFCB68F54278D

Nucinella nakremi sp. nov. (Fig. 4) Diagnosis. A small Nucinella having a nuculoid shape, smooth shell except for growth lines. Prosogyrate beak, one to three subumbonal teeth. Ligament amphidetic and does not invade the hinge plate. Holotype. Disarticulated left valve, NHMUK PI MB 1219, LD-04; length = 1.1 mm, height = 1.1 mm. Paratype. Disarticulated left valve, NHMUK PI MB 1220, LD-04; length = 0.9 mm, height = 0.8 mm (transposed hinge). Other material. Two specimens from LD-04 (NHMUK PI MB 1221–1222). Derivation of name. Named after Dr Hans Arne Nakrem in recognition of his work on Permian and Triassic fossils from Svalbard. Description. Shell small, nuculoid and ovate. Posterior dorsal margin distinct, slightly incurved; posterior margin rounded. Inequilateral, prosogyrate, with beaks close to anterior margin. Umbo prominent. Smooth, thin shell with very weak growth lines. Monomyarian: posterior adductor muscle scar absent; anterior adductor large, oval. One to two subumbonal, pointed blade-like teeth plus one anterior tooth. Ligament amphidetic, prominent, external does not invade the hinge plate. Remarks. These specimens differ from other described nucinellid species in having fewer hinge teeth, a more elliptical shape and a prosogyrate beak. Such differences may occur during the ontogeny of Nucinella (e.g. Bernard 1898) and so are not sufficient for assignment to a separate genus. These specimens are, however, considered to represent a separate species rather than an intermediate ontogenetic stage between the protoconch and adult stage of Nucinella taylori . During ontogeny, the shape, size and position of nucinellid subombonal teeth also vary: in earlier stages of development they are more rounded and later they develop a chevron-blade shape with the older teeth making space below the beak for thinner, newer ones (Bernard 1898; La Perna 2004). In contrast, the subumbonal teeth of specimens assigned to N. nakremi and N. taylori have comparable shapes, and so indicate a similar stage of development. ...