Class Demospongiae Sollas, 1885

Abstract

Demospongiae (Porifera) have discrete cellular elements, parenchymella or blastula larvae, with either viviparous or oviparous reproduc- tive strategies. The skeleton is composed of monaxonic or tetraxonic siliceous spicules (never triaxonic) bound together with spongin in discrete fibres or loosely aggregated, and ubiquitous collagenous filaments forming the ground substance of the intercellular matrix. Spicules and/or fibres, or both, may be absent in some taxa, and several other groups with solid calcitic or siliceous skeletons are also included (‘sclerosponges’, ‘sphinctozoans’, ‘lithistids’) rendering the class morphologically heterogeneous. Three subclasses are recog- nised based on larval morphology, reproductive strategy, tetraxonid versus monaxonic megascleres, and microsclere geometries, although these divisions require further refinement, and as such they are often ignored by contemporary authors. Demosponges include about 85% of all described Recent species, some are freshwater but predominantly they are marine species living from the intertidal to the deepest seas, with around 15 orders (the exact number still in contention), 88 families, and about 500 valid genera.