One species becomes two: The case of Chione Cancellata, the resurrected C. elevata, and a phylogenetic analysis of Chione

摘要

The common tropical western Atlantic venerid bivalve, Chione cancellata (Linnaeus), is revised on the basis of morphological, morphometric and phylogenetic analyses of conchological characters. Specimens inhabiting waters off the United States and Central America south to Belize comprise a separate species, described originally by Say as Chione elevata. The morphological and morphometric examination of numerous samples of both species supports the separation, pointing to differences of shell sculpture, hinge morphology and relative size of the pallial cavity. Morphological differences in sculpture suggest different functional characteristics of the species. A phylogenetic analysis of all extant species of Chione s.s. fails to resolve the relationship between C. cancellata and C. elevata. The parapatric separation of the two species reflects an ancient division of the tropical/sub-tropical western Atlantic into the northern Caloosahatchian Province and southern Atlantic Gatunian Province. This division dates back to at least the Early Pliocene. The fact that the differences between these two distinct species have been overlooked by systematists for almost 200 years suggests that we should re-examine western Atlantic species with broad geographic distributions similar to that of C. cancellata. It also suggests that we should pay closer attention to the taxonomy of common, ubiquitous species.