like all animals, sponges, possess some sort of a skeleton that gives their bodies shape. In zoology, a skeleton is defined as a fairly rigid structure of an animal, irrespective of whether it has joints and irrespective of whether it is biomineralized. The mesohyl functions as an endoskeleton in the majority sponges, and is the only skeleton in soft sponges that encrust hard surfaces like rocks. commonly the mesohyl is stiffened by mineral spicules, by spongin fibers or both. Spicules can be made of silica or Calciuom carbonate. they also vary in shape from simple rods to three-dimensional "stars" with up to six rays. Spicules are produced by Sclerocyte cells, and can either be separate, connected by joints, or fused.
Some sponges also secrete exoskeletons that lie completely outside their organic components. For example, sclerosponges(or "hard sponges")have massive calcium carbonate exoskeletons over which the organic matter forms a thin layer with choanocyte chambers in pits in the mineral. These exoskeletons are secreted by the pinacocytes that form the animals' skins.
Some sponges also secrete exoskeletons that lie completely outside their organic components. For example, sclerosponges(or "hard sponges")have massive calcium carbonate exoskeletons over which the organic matter forms a thin layer with choanocyte chambers in pits in the mineral. These exoskeletons are secreted by the pinacocytes that form the animals' skins.