Sponges are also known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. ” The fertilized eggs form larvae which swim off in search of places to settle. Most species use sexual reproduction, releasing sperm cells into the water to fertilize ova that in some species are released and in others are retained by the “mother. Structures such as canals, chambers, and cavities enable water to move through the sponge to nearly all body cells. Since water is vital to sponges for excretion, feeding, and gas exchange, their body structure facilitates the movement of water through the sponge. As their name suggests, Poriferans are characterized by the presence of minute pores called ostia on their body. Primarily, their body consists of a thin sheet of cells over a frame (skeleton). Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silica. The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where nutrients are deposited, and leaves through a hole called the osculum.
Sponges do, however, have specialized cells that perform specific functions. Therefore, sponges lack true tissues and organs in addition, they have no body symmetry. However, unlike higher metazoans, the cells that make up a sponge are not organized into tissues. Unlike Protozoans, the Poriferans are multicellular. (common name: yellow Picasso sponge) belongs to class Hexactinellida, and (c) Acarnus erithacus belongs to class Demospongia.
\( \newcommand\): Types of sponges: (a) Clathrina clathrus belongs to class Calcarea, (b) Staurocalyptus spp.
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