Sponge, Spongilla lacustris, Spongillidae, Sycon, Demosponge
Spongilla is a genus of freshwater sponges in the family Spongillidae found in lakes and slow streams. Sponges of the genus Spongilla attach themselves to rocks and logs and filter the water for various small aquatic organisms such as protozoans, bacteria, and other free-floating pond life. Unlike marine sponges, freshwater sponges are exposed to far more adverse and variable environmental conditions, so they have developed gemmules as a means of dormancy. When exposed to excessively cold or otherwise harsh situations, the sponges form these gemmules, which are highly resistant "buds" that can live dormant after the mother sponge has died. When conditions improve, the gemmules "germinate" and a new sponge is born.
Spongilla was used by John Hogg in the 19th century to attempt to justify a fourth kingdom of life.