Crosseolidae, a new family of skeneiform microgastropods and progress toward definition of monophyletic Skeneidae

摘要

Preliminary review of 130 available genus-group names for the notoriously polyphyletic group of skeneiform microgastropods has revealed a concentration of biodiversity in Australasia, primarily on the shelf and on or in clastic substrates. Forty-four of the names are based on type species from Australia or New Zealand, and some of the most speciose genera are abundantly represented and well preserved in the Cenozoic fossil record. Many skeneiform species were not illustrated at the time of description, and remain unillustrated except by inadequate line drawings. Features observed in scanning electron micrographs are used to define a set of new shell characters and to name and diagnose a new vetigastropod family Crosseolidae. Diagnostic features are the shallow anterior canal at the base of the columellar lip, a prominent umbilical keel, and a pseudumbilicus between the umbilical keel and the sharply defined inner lip. The shell of the type species of Crosseola, C. concinna (Angas, 1868), is illustrated with SEM for the first time, along with variation in shells of Crosseola striata (Watson, 1883). Three additional genera are assigned to the family: Conjectura Finlay, 1927, Conradia A. Adams, 1860, and Crossea A. Adams, 1865. Dolicrossea Iredale, 1924 is excluded on external anatomical evidence that the type species is a rissooidean caenogastropod. Intraspecific variation in crosseolids is partly a consequence of terminal growth features: adult variciform thickening of the outer lip, descending suture, and modifications of the columella and umbilical region. A restrictive definition of Skeneidae is provided along with examples of Australasian genera that can be allocated confidently to other families. Three predominantly Australasian groups of Cenozoic skeneiform taxa are identified for intensified study and potential allocation to new families. The constituency of vetigastropod family-groups and inferences of their relationships are too poorly resolved at this time to warrant the use of superfamily names.