Irregular growth in Chlamys islandica (Müller, 1776)

A remarkable shell was found in 1969 during an examination of the intertidal zone of the small island of Fjellvaeröy, at the entrance to Trondheimsfjorden, Norway. The shell consists of two empty valves, each having a length of 51 mm, height 48 mm, and width 32 mm. On closer examination the shell was identified as Chlamys islandica (Müller, 1776) (fig. 1). C. islandica has a mainly subarctic, discontinuous circumpolar, distribution, but does not occur in typical, high arctic sea areas (Ockelmann, 1958).