LABORATORY OBSERVATIONS ON THE LIFE-HISTORY OF THE ISOPOD SPHAEROMA-QUADRIDENTATUM SAY, 1818

Adult Sphaeroma quadridentatum were maintained in the laboratory for u p to ten months. It was found that males exhibit terminal molts, but f emales continue to molt until they die. Mature females alternate repro ductive and resting intermolt periods, and these periods are character ized by distinct oostegite morphologies. Immature females have small r ounded oostegites; brooding females have large, overlapping oostegites , and females in the resting stage have small oostegites with arrow-sh aped, angled tips. Amplexus only precedes a reproductive molt, but is not a prerequisite for fertilization. Copulation occurs in the interva l between the female's shedding the posterior and anterior parts of th e exoskeleton. Brood sizes ranged from 14 to 67, (x) over bar = 33.7+/ -11.3. Offspring were cultured to maturity in the laboratory, but this took as long as five months, and there was a mortality rate of 48%. G iven the relatively lengthy time to maturity, and the relatively high rate of juvenile mortality, culturing this species for use in bioassay s is not cost-effective.