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STARFISH (ASTEROIDEA)
STARFISH (ASTEROIDEA)
Starfish belong to the phylum of echinoderms. The typical feature of echinoderms is that they have five rays of radial symmetry. This is best seen in the starfish with its 5 arms. There are around 1600 species found in the world's oceans. Starfish have no eyes. However, there are several light-sensing cells at the tips of their arms that enable them to perceive differences in brightness in their surroundings. Starfish also have chemoreceptors on their skin that enable them to recognize nearby prey. They can also detect the gradient of the salinity of the water and move to the area where they prefer to live.
They move around with little feet on the underside of their arms that look like suction cups.
The mouth opening is located in the middle of the body, also on the underside. This makes it invisible to us divers. Depending on the genus, some starfish feed on algae and mud, others are scavengers and the predatory hunters among the starfish eat molluscs, snails and even crabs. Reproduction takes place in different ways. There are asexual species, hermaphrodites, hermaphrodites and asexual reproduction. Fertilization does not take place in direct contact, but in open water. As a free-swimming larva, it attaches itself to the bottom and then undergoes metamorphosis to become a juvenile starfish, as we see and know it with its 5 arms.
Photos: Johann Vifian
Sources: Coral reef guide and Red Sea reef guide / Wikipedia