Life‐cycles of lotic populations of Spongilla lacustris and Eunapius fragilis (Porifera: Spongillidae)

Abstract

SUMMARY. The life‐cycles of green and white morphs of the freshwater sponge Spongilla lacustris were examined in the light of past evidence that zoochlorellae may augment their sponge host's nutrition. Field collections from a lotic population of S. lacustris were supplemented by laboratory experiments on gemmule hatching and gemmule size. Both white and green S. lacustris produced sperm for a 6‐week period in 1976 starting in the middle of May. Out of thirty white and thirty green sponges examined during this period, twenty white and ten green sponges contained sperm. Sperm production in both morphs was limited primarily to the basal 3.18mm of sponge tissue, and the density of sperm packets in the two morphs was the same. Out of 180 white and green sponges examined in 1976, only four eggs, no embryos, and no larvae were observed. White sponges gemmulated a week or two earlier, and produced smaller gemmules which were more uniform in size than those of green sponges. White and green gemmules hatched synchronously in the spring. In 1977 one female and numerous male specimens of S. lacustris, and numerous females but no males of another sponge, Eunapius fragilis, were found. The life‐cycles are discussed in the light of other recent studies on freshwater sponges.