抄録
All species of freshwater sponges belong to the suborder Spongillina (Phylum Porifera) and are classified into seven families. Some families (such as Spongillidae comprising about 150 species) are geographically widespread, while others (such as Lubomirskiidae) are endemic to small areas. Spicules exsist in a variety of forms and are most important in the identification and classification of species and higher taxa. Other important key characters for identification are size, form and structure of gemmules, the gemmule coat, and micropyle. Most freshwater sponges produce gemmules, which are resistant bodies and asexual propagules. In Japan, the timing of gemmule production varies among species. Some species are hatched from gemmules in early spring and produce gemmules in early summer when water temperatures have not reached the maxima. Green color of freshwater sponge bodies is caused by the presence of algal symbionts. The algal symbionts are classified into two major groups based on the presence or absence of pyrenoid. In Spongilla lacustris, transfer of symbionts from parents to the next generation has been observed in both sexual and asexual reproduction. The classification of symbionts in several sponge species is currently under investigation using culture and molecular biological methods. Whether host specificity exists in these symbiotic algae is also under investigation. All Japanese species belong to the family Spongillidae. The Japanese species have been classified into 25 species in 11 genera. Recently, Heterorotula multidentata and Trochospongilla pennsylvanica have conspicuously increased in their geographical range in Japan, although they were not recorded before World War II. They may be exotic species introduced by human activity.
