Sex reversal in a freshwater sponge.

Spongilla lacustris exhibits a type of alternative hermaphroditism, new to the phylum, in which a sponge may be exclusively male or female during the period of sexual reproduction one year and the opposite sex the next year. This form of sexuality may facilitate larva production and thus dispersal following colonization of a new habitat. Gametogenesis occurs shortly after gemmule hatching in both males and females but slightly later in males.