Laboratory Observations On the Life History of the Isopod Sphaeroma Quadridentatum Say, 1818

Abstract

AbstractAdult Sphaeroma quadridentatum were maintained in the laboratory for up to tcn months. It was found that males exhibit terminal molts, but females continue to molt until they die. Mature females alternate reproductive and resting intermolt periods, and these periods are characterized by distinct oostegite morphologies. Immature females have small rounded oostegites; brooding females have large, overlapping oostegites, and females in the resting stage have small oostegites with arrow-shaped, angled tips. Amplexus only precedes a reproductive molt, but is not a prerequisite for fertilization. Copulation occurs in the interval between the female's shedding the posterior and anterior parts of the exoskeleton. Brood sizes ranged from 14 to 67, x = 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%. Given the relatively lengthy time to maturity, and the relatively high rate of juvenile mortality, culturing this species for use in bioassays is not cost-effective.