Anatomy and affinities of cocculinid limpets (Mollusca, Archaeogastropoda)

The anatomy of seven cocculinid species, representing four genera, is described. Two new genera are erected, Paracocculina and Coccocrater, and a comparative account of all cocculinid species so far anatomically investigated is given. Definitions of six genera, mainly based on anatomical data, are presented. Variation at the species level is also discussed. The closest relatives of the Cocculinidae are found in the Bathysciadiidae, sharing a distinct gill type and similar coelomic conditions. Therefore, both families are united as the Cocculinoidea. The Lepetelloidea (Lepetellidae, Pseudococculinidae, Osteopeltidae, Bathyphytophilidae (?), Cocculinellidae, Addisoniidae and Choristellidae) are more distantly related and are classified, together with the Cocculinoidea, within the suborder Cocculiniformia. The Cocculiniformia are regarded as one of the earliest offshoots at the archaeogastropod level of organization, being secondarily modified in several respects.