Shell structure characteristics of pelagic and benthic molluscs from Antarctic waters

The surface of the shell of the pelagic Antarctic gastropod, Limacina helicina antarctica forma antarctica, was smooth, with rib-like structures also observed. The larger specimen, with six to seven whorls, had visible ribs on its most outer whorl. The shell thickness of L. helicina antarctica forma antarctica was very thin, approximately 5-7 μm, on an individual with a shell diameter of 1.4 mm. Shell microstructure, as examined by SEM, was composed mostly of a crossed-lamellar structure. Shell thickness of the dominant benthic bivalve Laternula elliptica, was approximately 99-132 μm on an individual of shell length 19 mm. It was composed of two calcareous layers, including a thick outer homogeneous or granular layer and a thin nacreous inner layer. The characteristics of shell structure are discussed with reference to previous results, and in terms of adaptation to Antarctic waters.