Phylum Porifera - The Sponges
Poriferans that live in fresh water all belong to the family Spongillidae. They are much like their marine relatives, being unmoving masses of cells that filter water for nutrients. They are common in shallow, clean waters such as lakes, rivers, and streams. If green, they may be mistaken for plants, but they actually have algae living inside them in a symbiotic relationship. They grow in mats, and may have lobes or branch-like structures.
General Life cycle - Sponges reproduce both sexually and asexually. Sexual reproduction involves the release of sperm into the water. The sperm is then taken up from the water by other sponges while they are filtering. Eggs are fertilized internally and develop into ciliated larvae. The larvae are released into the water, swim to a new location, and quickly develop the adult form. Asexual reproduction is accomplished when fragments break off and generate new individuals or when spore-like gemmules are formed and develop into new individuals.
Identification - Sponges have no organs. Their body is composed of loosely organized tissues. The surface features many tiny holes where water is drawn in and other larger holes where water is expelled.
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