Sponge - Distinguishing Features

Distinguishing Features

Further information: Cnidaria and Ctenophore

Sponges constitute the phylum Porifera, and have been defined as sessile metazoans (multi-celled animals) that have water intake and outlet openings connected by chambers lined with choanocytes, cells with whip-like flagella. However, a few carnivorous sponges have lost these water flow systems and the choanocytes. All known living sponges can remold their bodies, as most types of their cells can move within their bodies and a few can change from one type to another.

Like cnidarians (jellyfish, etc.) and ctenophores (comb jellies), and unlike all other known metazoans, sponges' bodies consist of a non-living jelly-like mass sandwiched between two main layers of cells. Cnidarians and ctenophores have simple nervous systems, and their cell layers are bound by internal connections and by being mounted on a basement membrane (thin fibrous mat, also known as "basal lamina"). Sponges have no nervous systems, their middle jelly-like layers have large and varied populations of cells, and some types of cell in their outer layers may move into the middle layer and change their functions.

Sponges Cnidarians and ctenophores
Nervous system No Yes, simple
Cells in each layer bound together No, except that Homoscleromorpha have basement membranes. Yes: inter-cell connections; basement membranes
Number of cells in middle "jelly" layer Many Few
Cells in outer layers can move inwards and change functions Yes No

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