How Do Sea Stars Move?
Each sea star had hundreds of tiny feet on the bottom of each ray. These are tube feet, or podia. These tiny feet can be filled with sea water. The vascular system of the sea star is also filled with sea water. By moving water from the vascular system into the tiny feet, the sea star can make a foot move by expanding it. This is how sea stars move around. Muscles within the feet are used to retract them.
Each ray of a sea star has a light sensitive organ called an eyespot. Though it can not see nearly as well as we do, sea stars can detect light and its general direction. They have some idea of where they are going.
Sea Urchins & Sand Dollars
Sea urchins, heart …show more content…
For a long time they were written off as ‘parazoa’. Today the rest of the Metazoans are considered to belong to Eumetazoa. Some molecular taxonomists think that there are two lineages of sponges, one more closely related to other more complex Metazoans than the other.
People often think of sponges as plants, rather than being animals. This misconception is due to some of the characteristics of the Porifera (Dawkins 2004). Like plants they do not move, i.e., they are sessile. They stay put in one place stuck to the bottom of the water- either salt or fresh. Also, they don't have muscles. Like plants they move at the cellular level (Dawkins 2004).
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The name Cnidaria comes from the Greek word “cnidos,” meaning stinging nettle. There are about 9,000 species of cnidaria, the most common being the jellyfish, sea anemone, and coral. Cnidaria come in two different body forms: free-floating or free-swimming form such as the jellyfish, and the stationary form such as the sea anemone. Both forms consist of a body surrounded by tentacles with stinging cells called cnidocytes. The body has a single opening or mouth, for taking in food and expelling waste.
Cnidaria have no organs, just a stomach cavity for digesting food. Cnidarians are carnivorous. They prey on organisms ranging in size from small plankton to larger animals such as starfish, sea slugs, fish and turtles. They capture prey using their tentacles. When prey comes in contact with the tentacles, harpoon-like stingers inject a toxin into the prey paralyzing or killing it. The cnidaria then uses its tentacles to push the prey into its mouth.
Humans frequently come in contact with cnidaria, particularly jellyfish. Most toxin from cnidaria tentacles do little more than irritate human skin. However, with some forms of cnidaria such as the sea wasp a sting can be