Facts about Sea Star

Sea stars are star-shaped invertebrates living on the rocky sea floor. There are about 1800 known living sea star species that are distributed across the globe. The greatest variety of these are found in the tropical Indo-Pacific. Some other regions where they are widely found are the temperate regions of Australia, the cold-temperate waters of the North Pacific (California to Alaska), and the tropical East Pacific regions. These marine creatures can be sized from ½ an inch to over 3 feet in diameter and can live up to 35 years. Leather Star, Vermilion sea stars and Cushion stars are some of the common sea stars along the Pacific coast.

Sea star is not a fish

Sea stars are often referred to as starfish, however, the point to be noted is that the sea star is not a fish, which is why marine scientists have preferred to change its name from starfish to sea star. Sea stars and fish come under Kingdom Animalia. However, since fish are vertebrates, they belong to phylum Chordata, and sea stars along with sea urchins, brittle stars, feather stars and sea cucumbers come under phylum Echinodermata. Echinoderms exhibit a radial symmetry, which means that their arms radiate from a central disk outwards. Echinoderms are also characterized by tube feet, an endoskeleton that is made up of ossicles and plates in their body wall (may be large or microscopic).

Sea stars are often brightly colored

Live sea stars are brightly colored, unlike the dull, colorless skeletons we find on the beach. When alive, they feature wonderful colors such as red, orange, yellow, pink, blue, green or even purple. They even exhibit patterns on their body such as mosaic-like tiles, spots or even mottles. These colors and patterns assist the sea star to camouflage itself from predators. The bright hues also keep predators away by scaring them off.

Arms of sea stars are not limited to the number '5'

We often come across pictures of sea stars with five arms and assume that they are five-armed marine creatures. On the contrary, sea stars' arms are not limited to 5. In fact, sea stars with 10, 25 and even 40 arms too exist. Cool isn't it! Moreover, each arm contains an extension of the body organs and body cavity.

Sea stars use tube feet for locomotion

Sea stars do not possess a jointed and movable skeleton for locomotion, instead their locomotion is carried out with the help of the water vascular system. This water vascular system has hundreds of projections called tube feet (suction cups) adorning its ventral side. When the creature contracts, water enters these tube feet and make it protrude from the body. They enable these creatures to move along a surface by latching themselves to the surface. The tube feet function in the form of a wave, and when one portion of the body's tube feet attach themselves to the surface, the other portion releases its grip, thereby enabling the sea star to move from one place to another.

Sea stars are carnivorous and have two stomachs

Sea stars are carnivorous and feed on shell fish, mussels, clams, sea anemones, gastropods, snails and small fish. Some even feed on sea urchins and sea cucumbers. They will feed on any animal they can get their stomachs on! Sea stars do not use their mouth to draw in food, instead they use their stomach. They possess two stomachs: cardiac stomach and the pyloric stomach, and use both for digestion. The sack like cardiac stomach is ejected out of the body through the mouth opening and is used to engulf and digest prey from the surroundings. The pyloric stomach is used solely for digestion of the partially digested food in the cardiac stomach. Since they can eject their their stomach into the surroundings, they are able to catch animals larger than their mouth would naturally allow, such as mollusks, arthropods and so on.

Sea stars have no brains or even blood

This is quite an interesting fact about sea stars: they lack blood. These marine creatures use the water from the sea to pump up through their body. Water enters the water vascular system through a sieve plate called madreporite, which it pumps into the tube feet for carrying out locomotion. Sea stars lack the presence of the brain, instead possess a very complex nervous system.

Sea stars can regenerate their lost arms

This is an remarkably interesting feature of sea stars. They can regenerate a lost arm and in some cases even the entire body. The vital organs in these creatures are located on the arms itself and so in cases when their arms are eaten by predators or get damaged, these creatures can regenerate fresh arms. From the central disc and one arm, an entirely new sea star can be formed (this can take up to a year).

Some sea stars help keep sensitive coral reefs clean by scavenging for food, thereby being quite useful in reef setups. Most of the sea star species are harmless, however, there is the poisonous variety (Crown of Thorns ) as well. These fascinating creatures are not listed as an endangered species. However, the rate at which water is being polluted, we cannot be sure what the future holds!