The evolution of the Ellobiidae with a discussion on the origin of the Pulmonata.

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Abstract
SUMMARY.: The primitive phonate family, the Ellobiidae, is discussed with reference to the structure, ecology and relationships of the following genera—Pythia, Ophicardelus, Cassidula, Ovatella, Leucophytia, Ellobium, Pedipes, Leuconopsis, Marinula, Rangitotoa, Melampus and Carychium. Ecologically, the family is shown to fall into four sections, a more primitive estuarine section, and sections containing marine intertidal, coastal terrestrial and inland terrestrial genera of rather more specialized character. In relation with detailed descriptions about to be published of the functional morphology of British ellobiids, a wider comparative account is now given of the digestive system and the genital ducts, and their evolution throughout the family. Further trends, chiefly concerning the adult and embryonic shell, are dealt with, in a discussion of the evolutionary pattern of the Ellobiidae. The frequent occurrence of parallel evolution, and the relative absence of adaptive radiation, or characters of obvious selective value, are noted. A scheme is proposed for the classification of ellobiid genera into subfamilies, which in some points departs from that of Thiele, based on radular studies by Odhner.A wider review is then given of the evolutionary significance of the Ellobiidae, with reference both to the evolution of pulmonates from prosobranchs, and to their relationships with primitive tectibranchs. Finally, the relationships of the Basommatophora and the Stylommatophora are discussed, and the significance of the Ellobiidae is pointed out, with reference to the origins of both groups. The Basommatophora are held to be a phylogenetically unnatural group. The Ellobiidae is the only family of this group that could have provided possible ancestors for Stylommatophora, and these are unlikely to have occurred among known genera. Reference is made to the geological evidence in support of the view of gastropod evolution presented from this study.

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