SOME LIFE-HISTORY OBSERVATIONS ON THE PEA CRAB, PINNOTHERES-TSINGTAOENSIS, SYMBIOTIC WITH THE BIVALVE MOLLUSK, SANGUINOLARIA-ACUTA

The pea crab, Pinnotheres tsingtaoensis, symbiotic with the bivalve mo llusk, Sanguinolaria acuta, was collected in the estuary of Bazhan Str eam on the west coast of Taiwan from May, 1992 to November, 1993. More than 90% of the bivalves were infested and most infested specimens (9 0-97%) hosted one crab. Two cohorts, i.e., year classes, of the bivalv es were observed in May, but only one was seen between July and Novemb er; the life span of the crab is less than 2 years at the site. Recrui tment of both the bivalves and the crabs apparently occurred between N ovember and May next year. Positive size correlation between hosts and symbionts was found in larger sized females, but was not consistent i n smaller sized males. All females had a soft carapace whereas most ma les had a hard carapace; females were less likely to leave the hosts t han males upon collection of the host bivalves. Females accompanied by males were more likely to carry eggs. Mating probably took place insi de the hosts where female crabs remained stationary, with males visiti ng different bivalves and spending much time outside the bivalves.