Phylum Echinodermata
Structures: The adults have a five point radial symmetry. They have the shape of a star. They have no freshwater or terrestrial representatives. Their five parts are arranged around central axis. They have a mouth on the underside and their anus is on the top. They have tentacle like structures called tube feet. Tube feet have suction pads situated at their extremities.
Body Covering/Support: they have a mesoderm skeleton composed of calcareous plates of ossicles. Each of these is composed mineralogically of a crystal of calcite. They also have a sponge like porous structure known as the stereom. The ossicles may be flat plates or bear spines, warts or granules and they are supported by tough skin. The skin contains cells that help support and maintenance the skeleton. They also have cells that detect the motion on the animal’s surface and sometimes have gland cells that secrete sticky fluids or even toxins. Respiration: they have a poorly developed respiratory system. They basically use their simple gills and their tube feet to take in oxygen and to pass out carbon dioxide.
Nervous System: They don't have brains but they have nerves running from their mouth into each arm or along the body. They also have tiny eyes at the end of each arm that detect only light and dark. Some of their tube feet are sensitive to chemicals which allows them to find the source of smells, such as food. |
Nutrition: They have a simple digestive system with a mouth, stomach, intestine and anus. Sea stars push their stomachs outside of their bodies and insert them into the pray. Then it unleashes digestive enzymes to liquefy the soft body parts of the prey and then slurps them up. Sea Cucumbers are suspension feeder they the buccal podia to capture food then stuff the particles into the buccal cavity. Sea urchins feed on algae and others collect zooplankton with their branched arms. While the brittle stars are filter feeders.
Circulation of Nutrients: They have a network of fluid filled canals that function in gas exchange, feeding and in movement because they don’t have a heart. These canals are referred to as an haemal system. This system helps them get bad gasses out of their bodies and good gasses in and helps transport blood and body fluids around the body cavity. The blood and fluids are pumped through the body by the water vascular system. This system also helps them move around by using changing fluid pressure. |
Reproduction: They reproduce sexually by dropping their eggs and sperm into the water to get fertilized. Females can release one hundred eggs at once. Larvae develop than settle on the seafloor as adults. They can also regrow themselves if a part of them falls off. Some also have the ability to asexually reproduce by dividing into 2 halves while they are still juveniles.
|
|