Freshwater sponges in Japan ; systematics and distribution

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It is the purpose of this research to survey the species of the freshwater sponges in their habitats and to make clear the relation between their distribution and environment. Eleven genus and 25 species of freshwater sponges have been reported in Japan. Sponges are known as filter feeders which eat bacteria or detritus and clean up the ambient water by retention of these particles.Sponges can live in rather filthy waters, but become extinct rapidly excess some degree of pollution. Our survey was done mainly at 35 points of the Lake Biwa (Biwa-ko) and the 10 points of the Lake Shinji (Shinji-ko).A) Biwa-ko : The followings are the 11 species of 8 genus and of freshwater sponges collected in Biwa-ko during the term of the project. 1. Spongilla lacstris 2. Stratospongilla clementis 3. Eunapius fragilis 4. Ephydatia muelleri 5. Ephydatia japonica 6. Heteromeyenia stepanowii 7. Heterorotula multidentata 8. Ephydatia fluviatilis 9. Trochospongilla philottiana 10 T. latouchiana 11. Radiospon … More gilla cerebellata. The previously reported species were all found except one, Spongilla inarmata, besides 4species were newly found in the Lake, E. fluviatilis, T. philottiana, T. latouchiana and H. multidentata. Concerning the distribution, S. clementis, the endemic species of the Biwa-ko, was reported to be distributed in all over the lake, but in the survey they were found only in the North Lake, whose water is the cleanest in the Biwa-ko. In the South Lake and near the cities of the North Lake, the genus of Eunapius, E. muelleri and E. japonica were rich, and these species were scarcely found in the northeast part of the lake.B) Shinji-ko and its vicinity : Surveys were done twice in Shinji-ko and which are brackish water lakes. In these lakes only Spongilla alba, the brackish water sponge, was distributed. At Shinji-ko, the distribution of the sponges deeply depends on the salinity of waters. In the Shinji-ko, (salinity 3.0%_0 to 0.6%_0), only S. alba was found. In the Funakawa, even in the freshwater area (salinity 0.5%_0 to 0.2%_0), S. alba was distributed. In the Funakawa, 4 true freshwater sponges were collected as well as S. alba. This shows that S. alba adapts to wide range of salinity, from brackish waters to fresh waters. Less