Sponges
Sponge, any of the primitive multicellular aquatic animals that constitute the phylum Porifera. They number approximately 5,000 described species and inhabit all seas, where they occur attached to surfaces from the intertidal zone to depths of 8,500 metres (29,000 feet) or more. The members of one family, the Spongillidae, are found in fresh water; however, 98 percent of all sponge species are marine. Adult sponges lack a definite nervous system and musculature and do not show conspicuous movements of body parts.
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freshwater sponge
Freshwater sponge, any of about 20 species of the genus Spongilla (class Demospongiae, siliceous sponges), a common, widely occurring group. Spongilla species are found in clean lake waters and slow streams....
glass sponge
Glass sponge, any of a class (Hexactinellida, also called Hyalospongiae, or Triaxonia) of sponges characterized by a skeleton that consists of silica spicules (needlelike structures) often united into...
siliceous sponge
Siliceous sponge, any sponge in which the main skeletal component is silica as opposed to calcium carbonate or fibrous organic materials only. More than 95 percent of all known sponge species have a siliceous...
horny sponge
Horny sponge, any sponge of the orders Dictyoceratida and Dendroceratida (class Demospongiae). It has a skeleton consisting exclusively of fibrous organic components. Most other sponges, by contrast, have...
calcareous sponge
Calcareous sponge, any of a class (Calcarea) of sponges characterized by skeletons composed entirely of calcium carbonate spicules (needlelike structures). Calcareous sponges occur mainly on the rocky...
archaeocyathid
Archaeocyathid, any member of an extinct group of marine organisms of uncertain relationships found as fossils in marine limestones of Late Precambrian and Early Cambrian age (Precambrian time ended about...