Dictionary.net

The phylum of sponges, the most primitive of multicellular animals. Their body is perforated with many pores to admit water, through which food is strained. All sponges are sessile and exhibit little detectable movement. Most are hermaphroditic. They are probably an early evolutionary side branch that gave rise to no other group of animals. Except for about 150 freshwater species, sponges are marine animals. They are a source of alkaloids, sterols and other natural products useful in medicine and biological research. (Dorland, 27th ed; from Barnes, Invertebrate Zoology, 5th ed, p71)