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.

• see Appendix Sponges 1

What are the main characteristics of Sponges?

They are loosely organized and lack true tissues. Their sizes are from a few millimeters to more than 2 meters in diameter. They don't have a symmetry The body of a sponge looks similar to a vase pierced with small holes and 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. Sponges do not have nervous, digestive or circulatory systems.

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?

Cnidarians (phylum Cnidaria) are mostly marine species (more than 10'000). The name Cnidaria comes from the Greek word "cnidos" which means stinging nettle.

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. It is characterized by the mouth and tentacles facing up, and the other side being anchored to a colony of the same creatures (like a coral reef). Medusoids are usually free swimmers, like jellyfish. Their tentacles and mouths are generally 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 which are used to subdue and capture food.