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Sea stars move by crawling along the seabed and over rocks and reefs. On the underside of their bodies, a groove extends from the mouth to the tip of each arm. Rows of slender tubes, called tube feet, line these grooves. They use the suction disk at the end of each tube foot to grip surfaces and crawl along.
Many sea stars are omnivores, feeding on both plants and animals. A sea star’s mouth is in the middle of the underside of the central disk and leads directly into a large, bag-like stomach. The sea star can push its stomach out through its mouth. When it feeds on a bivalve (such as an oyster), it attaches its tube feet to the two halves of the animal’s shell and pulls the shells halves apart, opening a tiny crack between them. Then the sea star pushes its stomach, turned inside out, through the crack in between the shells. A sea star can slide its stomach through a crack no larger than the thickness of a piece of cardboard! The stomach surrounds the animal’s soft body, slowly digests it, and the food is absorbed through the lining of the stomach.
Most sea stars have separate sexes. They reproduce by releasing eggs and sperm into the sea through reproductive organs (small holes) between their arms. The eggs and sperm meet by chance in the water column and fertilisation occurs. The fertilised eggs hatch into microscopic swimming larvae, forming part of the plankton. After a while, each larva settles down on the sea bottom and develops into a sea star. Most sea stars live for 3 – 5 years, but some may live to 7.
Threats include; human disturbance (standing on reef and coral, collecting) and pollution.