Contributions to the biology of Tagelus plebeius (Bivalvia: Tellinacea) in Galveston Bay, Texas.

Monthly quantitative population samples of 100 to 200 clams each were taken from an intertidal mud flat during the year 1968. Individuals were measured and weighed to get growth data and were checked for the presence of symbiotic organisms. Various aspects of ecology, such as habitat, behavior and predation, were observed in the field. Population studies showed high densities of clams (to 300 per sq. meter) during the early spring, declining sharply in the fall. Larval clams settled in the spring and grew rapidly until the following winter. The breeding stock of large adults constituted a relatively small percentage of the population throughout the year. Clams were isolated experimentally at various salinities in order to find the limits of their tolerance. Salinities ranging from 5 to 35 ppt produced little change in the feeding rate of T. plebeius, and these clams survived prolonged isolation at both of these salinity extremes, indicating a high degree of euryhalinity. High fall mortality was found to occur in the field, which may be related to the presence of Labyrinthomyxa-like fungus parasites in the tissues of the clam. Larval trematodes of the families Gymnophallidae and Fellodistomatidae and larval tapeworms of the order Tetraphyllidea are here first reported as parasites of T. plebeius. The trematode sporocysts were observed to cause damage to the gonad and digestive gland of the host.