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)
[pic]An Orange Finger Sponge (Neoesperiopsis rigida)
[pic](*) The anatomy of a sponge.
[pic]What the skeleton of a sponge looks like.
[pic](*) Purple and Yellow Tube Sponge
(1) "Sponge," Microsoft Encarta 96 Encyclopedia, 1993-1995 Microsoft Corporation.
BACK TO THE INVERTEBRATES PAGE!
Corals come in all shapes and sizes--some are reef-builders while others are non reef-builders: The reef builders are the corals that can be seen in the Great Barrier Reef off Austrailia. Reef builders build high structures composed of living and non-living materials. The living materials are most often sponges, algae, and the corals themselves. The non-living materials are most often the discarded shells of dead bivalves (clams, mussels, etc.) and other CaCO3 materials. Coral reefs grow about a meter every one thousand years, so you see why it's very difficult for a reef to recover if it is destroyed. An example of a reef-builder.
Non reef-builders usually inhabit the bottom of more shallow areas of the ocean. They do not build high structures. An example of a Fire Coral, a non reef-builder.
What is a Coral...