Article: The shell structure, mineralogy and relationships of the Chamacea (Bivalvia)

The superfamily Chamacea is a group which has constantly confused systematists concerning its relationship with other bivalves. Various authors have related it to the Cardiacea, Veneracea, Crassatellacea, Lucinacea, and the rudists (Hippuritacea).Most classifications have placed the Chamacea with the rudists; Newell (1965) placing them into the Hippuritoida, a relationship which Yonge (1967) considers beyond doubt. From a review of hard and soft part anatomy, especially shell-structure, dentition, and mineralogy, it seems likely that the Chamacea arose from a group of byssate Cardita in the early or middle Cretaceous. Similarities to the rudists are the result of convergent adaptions to a similar mode of life, and there is no real indication of relationship.The Chamacea should be removed from the order Hippuritoida and placed in the order Veneroida.