SYSTEMATICS OF THE GENUS GASTROCHAENA (MOLLUSCA, BIVALVIA, SUPERFAMILY GASTROCHAENOIDEA)

The genus Gastrochaena Spengler, 1783, comprises all Gastrochaenoidea with sharply erect, posterior commarginal lamellae, relatively simple hinges (i.e., lacking distinct myophores), relatively short siphonal borings, and without strongly projecting baffles in the boring lining at the base of the siphons. Sixteen nominal Recent species of Gastrochaena have been published since 1783. Of these, the only widely used names today are G. cuneiformis Spengler, 1783,G. gigantea Deshayes, 1830, and G. philippinensis Deshayes, 1855, for Indo-West Pacific species; G. ovata Sowerby, 1834, and G. denticulata Deshayes, 1855, for Eastern Pacific species, and G. ovata for Western Atlantic species. Morphometric analysis of type and non-type specimens of Recent Gastrochaena in European, American, and Australian museums, plus new collections from Thailand, the Great Barrier Reef, Hawaii, Panama, and the Caribbean indicate that this genus is represented by 6 extant species, i.e., G. cuneiformis, G. ruppelli, G. ovata, G. denticulata, G. macroschisma, and G. brevis. The latter two appear to represent a distinct evolutionary lineage from the other four species. The most widespread extant species of Gastrochaena is G. cuneiformis, with distinct subspecies in the tropical Indo-West Pacific, the Arabian Sea, the warm temperate Japanese Region, the warm temperate Southern Australia Region, the Hawaiian Islands, the tropical Eastern Pacific,the tropical Western Atlantic, and the warm temperate Carolina Region. Late Cenozoic speciation and subspeciation in Gastrochaena reflects three major influences: (1)the biogeographic history of the tropical oceans, (2) climatic differences and correlated substrate differences between tropical and warm temperate regions, and (3) localized morphological specializations for boring into more resistant substrates, as in the northern Arabian Sea and in Panama Bay.