Embryonic, Larval and Postlarval Development of the Tropical Clam, Anomalocardia brasiliana (Bivalvia, Veneridae)

Anomalocardia brasiliana (Gmelin, 1791) is a venerid clam, distributed from the West Indies to Brazil, which lives shallowly burrowed in muddy sands of mangrove lagoons in Guadeloupe. Development from induced spawning to metamorphosed juveniles is described by using light and scanning electron microscopy. The shell-field appears at the gastrula stage, 6 h after fertilization, and rapid embryonic development results in straight-hinge veligers, 18 h after fertilization. These swimming veligers develop to swimming-crawling pediveligers, then to benthic plantigrades with functional elongated gill filaments without interruption in 15 days. The transitional arched structures observed at the end of the pediveliger stage were called 'ctenidal crypts' to distinguish them from functional gill filaments which exist only in metamorphosed juveniles. Metamorphosis, which occurs without a special environmental cue, is completed with the differentiation of the siphons in 300 um juveniles. Thus, there is no delay of metamorphosis in this species whereas a developmental hiatus has been described in most planktotrophic bivalves. Juveniles, 1 mm in shell-length with the triangular shape, pointed posterior end and brown zig-zag stripes on the shell, typical of A. brasiliana have been obtained 7 weeks after fertilization. However, a large variability of individual sizes and developmental stages within the same batches may indicate a high genetic variability.