REVISION OF THE SUPRASPECIFIC CLASSIFICATION OF MARGINELLIFORM GASTROPODS

The supraspecific classification of marginelliform gastropods, formerl y treated as the single family Marginellidae, is revised. This revisio n is based on all available information for all Recent species plus a representative sampling of the fossil fauna, and includes all Recent a nd fossil genus-group names. All published information is summarized, and additional dissections, concentrating on the foregut and radular m orphology, are reported, nearly doubling the number of species known a natomically. Fundamental differences between two groups of marginellif orm gastropods are discussed. Cystiscids have internal shell whorls pa rtially resorbed and columellar plications reduced internally. Their r adular morphology differs fundamentally in having narrower, more numer ous rachidian plates, a different subradular membrane structure, separ ate odontophoral cartilages, and in the plate development on the poste rior end. They differ anatomically in the possession of a typical neog astropod radular sac. True marginellids have unmodified internal whorl s and columellar plications continuous internally. Their radulae are s horter and broader, odontophoral cartilages are fused anteriorly, and a marginellid buccal pouch is present. The Olividae have the same spec ializations as the cystiscids and these two groups are considered to h ave a common ancestry. On this basis, the Cystiscidae is recognized as a valid family and not considered to be closely related to the Margin ellidae. The ancestry of the Marginellidae is discussed and the family is considered to be related to the Volutidae. The Cystiscidae is divi ded into four subfamilies, three of which are described as new. Nine R ecent genera, plus one fossil genus, are recognized. Plesto-cystiscus, new genus, is described on the basis of a triserial radula and other primitive characters. The Marginellidae is divided into two subfamilie s and three tribes, two of which are new. A total of 22 Recent genera are recognized in this family, plus nine fossil genera. Serrataginella , new genus, is described on the basis of its unique radular and shell morphology. A systematic section lists synonyms and type species of e ach genus, along with a diagnosis, description, and summaries of the d istribution and fossil record. The phylogeny of both families is discu ssed, and keys to Recent genera in both groups are presented.