Sea Stars or Starfish as they are better known are fascinating creatures of our Oceans. Closely related to sea urchins, sea cucumbers and sand dollars, starfish are not really fish. They are echinoderms and marine scientists are trying to get people to use the name ‘Sea stars’ instead of the misleading but popular Starfish tag.
There are over 2,000 species of Sea stars across the World’s Oceans. They typically have five “arms” and while these are the most common of sea stars, species with 10, 20 and even 40 arms exist. Starfish or Sea stars rather, have radial symmetry which makes them distinctive from other sea animals. They come in striking colors that can work as a camouflage and inspite their bony or spiny upper surface, are very attractive creatures.
The seemingly passive and helpless sea stars can be quite the predators underwater. They feed on clams, oysters, snails and other mollusks that are significantly bigger than the size of their mouth which is placed on its underside. If you’ve ever tried to open the shell of a clam or mussel open, you’ll know just how difficult this task is. Yet, sea stars easily wrap their arms around the animal’s shell and pull it open with the help of its tube feet,which is also how it moves around on the sea bed. Then it does something amazing- it eats its prey with their stomach inside out! It pushes its stomach through its mouth and into the shell of clams, scallops or mussels and then digests the animal before sliding its stomach back into its own body. In essence, starfish have two stomachs, the one can be extended outside its body and the second pyloric stomach to which it is transferred for further digestion.
Another very interesting ability of sea stars is how it is able to regenerate lost arms and can regrow an entire new arm in time. It uses this ability to its advantage when they are threatened by predators- the smart starfish drops an arm to get away if needed. Some species can even grow an entirely new sea star just from a portion of a severed limb as that’s where it houses most of its vital organs, some however, require their central body to regenerate.
Sea stars have eyes at the end of each arm, but in reality can’t see very well. They can sense light and dark but not distinct shapes nor colors. Their tube feet however are sensitive to chemicals and uses this to locate food.
So, the next time you come across a sea star when you Scuba dive or just walk along a beach you can truly see them for the stars they are!
* Photo credits: photos by TheMarque, Razvan Marescu, paulshaffner on flickr.
