Parameter Tree:
EARTH SCIENCE > BIOLOGICAL CLASSIFICATION > ANIMALS/INVERTEBRATES > SPONGES

Definition:
Sponges are multicellular organisms with no discrete tissues and organs
but with a skeleton composed of collagen (with or without mineral
elements), and a tubular water filtration system driven by specialized
uniflagellate cells.  They have a free living sessile habit and are mainly
marine at all depths and latitudes but some occur in freshwater. 


Reference:
Burn, David M. Animal World. 1980. Octopus Books Ltd. London.