Evolution and systematics

All living Cocculiniformia have cap-shaped shells. The earliest cocculiniform limpets are found in Tertiary sediments of New Zealand where they are associated with fossilized wood. They are likely descended from coiled snails, like other living limpets, but like the patellogastropods, possible ancestors have not yet been identified in the fossil record.

Living cocculiniform limpets were unknown until the advent of deep-sea exploration in the seventeenth century. At the time, a variety of substrates were recovered by bottom dredges, including cephalopod beaks, waterlogged wood, fish and whale bones, and the egg cases of sharks and skates; all of these substrates were found to have small white limpets living on their surfaces. Almost every species was placed in different genera and families based on their gill morphology and digestive systems, which were also loosely correlated with the different substrates from which these limpets came. In the late twentieth century, these families were grouped into the Coc-cuiliniformia. However, subsequent phylogenetic analyses based on morphology and molecules showed that there were actually two convergent groups represented. This resulted in the Cocculiniformia being restricted to the Cocculinoidea, while the Lepetelloidea were transferred to the Vetigastropoda, where they represent an early branch in that taxon. However, the placement of the Cocculinoidea among other gastropods remains problematic. Some workers would place it near the base of the gastropod tree, thereby representing an early offshoot in gastropod evolution, while other placements include a possible relationship to the Neritopsina.

The order Cocculiniformia includes two families: the Coc-culinidae and the Bathysciadiidae.

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