There are about 5,000 species of sponge, mostly marine and few freshwater species. In sea they occur up to a depth of 8,500 m and mostly flourish in warm waters. Size can vary from a few cm to several metres. The body shape is highly variable.
Class CALCAREA (=CALCISPONGIAE). Small marine sponges with calcareous spicules.
Subclass HOMOCOELA. Choanocytes line the spongocoel. Ex. Leucosolenia; Clathrina.
Subclass HETEROCOELA. Choanocytes line the radial canals. Ex. Sycon; Grantia.
Class HEXACTINELLIDA (=HYALOSPONGIAE). Marine glass sponges with 6-rays spicules.
Subclass HEXASTEROPHORA. Spicules hexasters, fused to form glass-like shiny vase. Found on hard surface. Ex. Euplectella.
Subclass AMPHIDISCOPHORA. Spicules amphidisc type, some form long spun glass type of root tuft to anchor on sandy bottom. Ex. Hyalonema.
Class DEMOSPONGIAE. Massive frame sponges with sponging fibres and siliceous spicules.
Subclass TETRACTINELLIDA. 4-rayed spicules. No sponging. Ex. Oscarella; Plankina.
Subclass MONOAXONIDA. Monoaxon spicules. Spongin present or absent. Ex. Cliona; Halichondria; Heliclona; Chalina; Spongilla; Ephydatia.
Subclass KERATOSA. Only sponging fibres. Dark horny sponges with leathery surface. Ex. Euspongia; Hippospongia; Phyllospongia; Chondrilla; Proterion.