The palaeobiology of nerineacean gastropods

Amongst nerineacean gastropods which have been preserved in fine grained carbonate sediments, remnants of a calcite rod system contained within the helically coiled body chamber can frequently be found. The position of these rods, their petrography and the presence of side branches suggest that they represent the original duct system within the digestive gland/gonad complex of the gastropod. The characteristic internal spiral folds secreted by the nerineids were emplaced between the major lobes of the digestive gland/gonad complex, possibly at the expense of the nutrient storage capacity. The absence of folds at the aperture and apex, together with the origin of the superfamily in the Lias, indicates that folding was not developed as a protective adaptation against durophagous molluscivores. Instead, the deposition of calcium carbonate internally enabled these gastropods to exploit the food resources of carbonate substrates, initially infaunally and subsequently epifaunally. Most of this ecological diversification was attained during the Bathonian and from this time, the Nerineacea became prominent members of shallow water Mesozoic carbonate communities.