Distinguishing Features
Further information: Cnidaria and CtenophoreSponges 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 |
Read more about this topic: Sponge
Famous quotes containing the word features:
“However much we may differ in the choice of the measures which should guide the administration of the government, there can be but little doubt in the minds of those who are really friendly to the republican features of our system that one of its most important securities consists in the separation of the legislative and executive powers at the same time that each is acknowledged to be supreme, in the will of the people constitutionally expressed.”
—Andrew Jackson (1767–1845)