Systematics of Indo-Pacific Philippia (Psilaxis), Architectonicid Gastropods with Eggs and Young in the Umbilicus

Abstract

The subgenus Psilaxis Woodring is distinguished from Philippia Gray, s.s., on the basis of differences in the shells, jaws, opercula, and doubtfully radulae. Only two species of Psilaxis, differing mainly in three protoconch characters, are recognized in the Indo-Pacific. Philippia (Psilaxis) radiata (Roding), with the generally smaller protoconch, is the most abundant and widespread species, ranging from South Africa and the Red Sea east to the Marquesas and the Hawaiian Islands ; it is thus both tropical and subtropical. Philippia (Psilaxis) oxytropis A. Adams has a larger protoconch and a disjunct range, being known only from the subtropical western and central Pacific Ocean-including Japan, the Hawaiian Islands, and New Zealand but excluding latitudes between 20 ° Nand 20 ° S. Young postlarval P. oxytropis live in the umbilicus of the adult shells, and in P. radiata one egg mass has been found in an umbilicus. Nevertheless it is concluded from the small egg size of P. radiata (average diameter 63μ) that both species have a long pelagic larval stage. Philippia hybrida (Linn.) is a Mediterranean species in the subgenus Philippia, s.s., and P. layardi A. Adams is a synonym of P. radiata. In Marqu esan P. radiata there is a noteworthy increase and bimodality in protoconch size that are attributed tentatively (with no chromosomal evidence) to polyploidy. Polyploidy perhaps also is involved in the origin of species of Philipp ia and in the origin of Psilaxis from Philippia, s.s. By the Miocene, Psilaxis seems to have displaced Philippia, s.s., from most areas except peripherally in the subtropics. The pyramidellid-like egg capsules of architectonicids are described for the first time, and the larvae are also opisthobranch-like. Philippia has a cuticularized esophageal tube and radular teeth similar ( analogous? ) to those in the Epitoniidae.