Phylum: Porifera
A sponge has differentiated cells and functionally distinct layers. The ameobocytes secrete spicules which stack up together to make the sponge. The choanocytes are composed of a flagellum and a collar (collar cells). The amoebocytes and choanocytes are the work force of the sponge--they create the body of the sponge.
The major sponge groups of today had an ancestor in the Cambrian period.
The sponges reproduce either sexually or asexually. When they reproduce sexually, they usually cross-fertilize. Eggs and sperm unite to make a free-swimming larva that settles on a different surface. Asexually, the sponge produces small, internal buds called gemules. These gemules each produce a new sponge. Sponges can also reconstitiute themselves if their cells are separated into a suspension. (1)
Pictures:
An Orange Finger Sponge (Neoesperiopsis rigida)
(*) The anatomy of a sponge.
What the skeleton of a sponge looks like.
(*) Purple and Yellow Tube Sponge
(1) "Sponge," Microsoft Encarta 96 Encyclopedia, 1993-1995 Microsoft Corporation.
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