Unique digestive system, trophic specialization, and diversification in the deep‐sea gastropod genus S caphander

Dietary specialization is known to be important for the evolution of C ephalaspidea gastropods, but still little is known about the overall trophic interactions of the group and the putative role of trophic ecology on diversification. The genus S caphander is a group of predominantly deep‐sea, infaunal cephalaspids with about 40% of its species (eight) occurring on the A tlantic O cean. They are carnivorous and have a unique digestive system with a large, strongly muscularized gizzard containing three sizable and heavily calcified plates. This work aims to describe the diet of S caphander , to evaluate if there is a functional relation between the anatomy of the digestive tract and exploitation of novel food resources, and to assess if dietary specialization may have played a role in the diversification of the A tlantic species of S caphander . Gut contents were studied from 31 specimens representing seven of the A tlantic species using scanning electron microscopy and light microscopy. The chemical composition of the gizzard plates was analysed by X ‐ray microanalysis and X ‐ray powder diffraction. Foraminiferans, including agglutinating forms, were shown to be the most important food item for S caphander ; bivalves, gastropods, scaphopods, and polychaetes with calcareous tubes were also found to form part of the diet. The gizzard plates were shown to consist of a phosphate‐rich amorphous component and a crystalline component identified as fluorite (hardness 4; M oh's scale). It is suggested that the ability of S caphander gastropods to prey upon organisms with hard tests, particularly agglutinating foraminiferans, is not only due to the hardness of the gizzard plates but to the cumulative effect of shape and hardness of the gizzard plates and relative size of the gizzard and associated musculature. No interspecific differences were found in the diet and morphology of the digestive tract, indicating that dietary specialization probably has not played a significant role in the diversification of Atlantic species of Scaphander . © 2013 The Linnean Society of London, Biological Journal of the Linnean Society , 2013, 109 , 512–525.