User:Annsli.Hilton/Spongilla

Overview
Spongilla is a genus of freshwater sponges with over 200 different species. Spongilla was first publicly recognized in 1696 by Leonard Plukenet and can be found in lakes, ponds and slow streams. Spongilla have a leuconoid body form with a skeleton composed of siliceous spicules. They are sessile organisms, attaching themselves to hard substrate like rocks, logs and sometimes to ground. Using their ostia and osculum these sponges filter the water for various small aquatic organisms such as protozoans, bacteria, and other free-floating pond life. Sponges of the genus Spongilla partake in symbiotic relationships with green algae, zoochlorellae. The symbiotic zoochlorellae give the sponges a green appearance and without them they would appear white.

Reproduction
Sponges are hermaphroditic organisms, producing both egg and sperm. Sperm is released from one sponge and brought in through the ostia of another sponge. Once the sperm reaches the body cavity it is fertilized and develops into a free-swimming larvae. The free-swimming larvae is released out the osculum and will eventually settle and attach elsewhere. Since the larvae are developed inside the spongilla it is viviparous.

Unlike marine sponges, freshwater sponges are exposed to far more variable environmental conditions, so they have developed gemmules as an overwintering mechanism. When exposed to excessively cold or other harsh conditions, the sponges form gemmules. Gemmules are highly resistant buds that can live dormant for extended periods of time. When conditions improve, the gemmules "germinate" and a new sponge is born.