Sponges Cnidarians 2BIbDF09 10/11

What are Sponges?

Sponges, from the Latin pore bearers, are very primitive animals of the phylum Porifera, more precisely they are the first multicellular animals. They evolved very early from colonial protists. Their ancestors are the choanoflagellates (group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals). There are between 8'000 and 9'000 species of sponges, depending of the textbook.
They are invertebrates, which are animals without backbones. There exist different sponges of different forms and different shapes, including tubes, fans, cups, cones, blobs, barrels, and crusts.

• see Appendix Sponges 1

What are the main characteristics of Sponges?

Sponges are loosely organized and lack true tissues. The body of a sponge has two outer layers separated by an acellular gel layer called the mesohyl (also called the mesenchyme). In the gel layer are either spicules (supportive needles made of calcium carbonate) or spongin fibers (a flexible skeletal material made from protein).
Their sizes are from a few millimeters to more than 2 meters in diameter. They don't have any symmetry.

The body of a sponge looks similar to a vase pierced with small holes and pores. It has thousands of pores. Water is drawn through the little pores into a central cavity, the spongocoel, then flows out the sponge through a larger opening, the osculum. In this process, they collect small particulate matter and tiny planktons, by the trapping action of the choanocytes, which are collar cells. That's why we call them filter feeders. Sponges do not have nervous, digestive or circulatory systems.

As adults, sponges are sessile. That means that they are permanently attached to a substrate and are unable to move on their own.
Most sponges are hermaphrodites (each adult can act as either the female or the male in reproduction). They produce sperm and eggs which are formed by aggregations of cells called amoebocytes in the body wall. During the proper time of the year, they release sperm cells into the sea. These cells are then captured using the same process the sponges use to capture food. The difference is that the sperm cells are moved to the "ova" of the sponge parent. And now the fertilization can take place. The eggs develop within the parent, the amount of time this takes depends on the species. When the eggs reach the "larvae" stage they are released back into the sea to seek out a place to settle and colonize.

Sponges can be either white, red, orange, green, yellow, brown, purple or black. They are known for regenerating from fragments that are broken off..

good. Maybe you could create an Appendix document showing the main characteristics of Sponges [[ Utilisateur:Pierre.brawand|Pierre.brawand]]

Where do Sponges live?

Of the 9'000 or so species of sponges, only about 100 live in fresh water, the rest are marine.

What are Cnidarians?

The name Cnidaria comes from the Greek word "cnidos" which means stinging nettle. Cnidarians (phylum Cnidaria) are mostly marine species (more than 10'000) and are the oldest of the true metazoan phyla . All the Cnidaria are aquatic and nearly all are marine.

What are the main characteristics of Cnidarians?

They are two different forms of Cnidarians body: Polypoid Shape or Medusoid Shape.
The polypoid is the shape of corals and anemones. Its characteristics are the mouth and the tentacles facing up and the other side is anchored to a colony of the same aspect: for example, a coral reef. Medusoids are jellyfish. They are free swimmers and their tentacles and mouth are pointed down (the opposite of polypoids) Cnidarians have a mouth and a simple digestive system at the center of their tentacles, that is the reason why they are considered as animals and not plants. They have a radial symmetry. All cnidarians use tentacles which have stinging cells to subdue and capture food. They generally eat small planktonic animals.
Cnidarians reproduce both asexually and sexually. The reproduction is made by budding. That is a process of asexual reproduction in which a new individual develops from some generative anatomical point of the parent organism.
*see Appendix Cnidarians 1

Where do Cnidarians live?

They live under water. Some Cnidarians live in the oceans and seas, and a few live in freshwater. But they mostly live in saltwater or oceans.

OK... good start but you should now produce more information... [ [Utilisateur:Pierre.brawand|Pierre.brawand]]

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