THE ECOLOGY AND REPRODUCTION OF A MARINE BIVALVE, MYSELLA PLANULATA (ERYCINACEA)

1. In Beebe Cove, a shallow sublittoral bay, the bivalve Mysella planulata is dispersed contagiously throughout the year. This dispersion is not associated with the mode of development of the species but may be correlated with non-random variability in the microhabitat. There is no evidence that M. planulata in Beebe Cove is symbiotically associated with any invertebrate species. 2. Mysella planulata has a life span encompassing four growing seasons and a maximum size of about 4.0 mm. About 50% of maximum length is attained by the end of the first growing season. 3. Mysella planulata is a simultaneous hermaphrodite. Spermatogenesis precedes oogenesis. The species is capable of self-fertilization and although no animals were ever observed to release sperm, the possibility of cross-fertilization is not ruled out. Egg production is limited to animals in excess of 1.7 mm. 4. Larvae are retained in the suprabranchial chamber to the straight-hinge stage of development. Upon release, the larvae are planktotrophic; starved larvae in culture grow slightly but will not metamorphose. Metamorphosis in culture occurs in about two weeks at 25° C. In the laboratory, larvae metamorphose over a wider range of size than in nature, probably reflecting predation pressure in nature. 5. Estimates of the potential reproductive contribution of the various age classes show that although the major burden is carried by animals in their 3rd season (0 + 2 class), older classes contribute significantly. This pattern is adaptive in unstable environments where high mortality of the 0-year class is probable. 6. On morphological grounds, M. planulata is believed to be a suspension feeder; probably feeding on very fine particulate organic matter.