Sea stars are marine creatures closely related to sea urchins and sand dollars (echinoderms). Its common name “starfish” is now being replaced by marine scientists to “sea star” because, well, it is not really a fish.

There are over 2,000 species of sea star living in all the world’s oceans, and they come in a variety of striking colors. Though they typically have five arms, some species can have less, or more, with some reaching up to 40 limbs.

photo by Nick Hobgood

photo by Mila Zinkova

These invertebrates have two stomachs–one is used for digestion, and the second one can be everted out to devour and digest its victim. They are carnivores that usually snack on shelled animals such as mussels and clams. Using their tiny, suction-cupped tube feet, most species have the remarkable ability to force open the shells of bivalve mollusks, and their sack-like cardiac stomach comes out from their mouth and flows out inside the shell. The stomach then swallows up the victim to digest it, and finally retracts back into the body.

photo by Nick Hobgood

photo by Nick Hobgood

photo by Paul Shaffner

These brainless creatures are famous for their ability to regenerate limbs, and in some cases, even their entire bodies; a few species can even grow an entirely new sea star just from a portion of a severed limb. This is made possible because they house most of their vital organs in their arms and their “blood” is actually filtered sea water.

The sunflower sea star (2nd photo here) is the largest sea star in the world. It has 16-24 arms that can grow up to 1 m (3 ft) across. Its color ranges from bright orange, yellow and red to brown and sometimes to purple.

photo by Nick Hobgood

photo by Wildcat Dunny

Some common sea star species include:

• Carpet sea star—is native to southern Australia.  They dwell on rock pools and can be found in four color variations: the cushion sea star has eight arms and can be any color or combination of colors; the Patiriella exigua is turquoise with five arms; the P. brevespina is purple with orange feet and six arms, and the P. gunii can be in any color and has six arms.

• Crown-of-thorns sea star (6th photo here)—is the second largest sea star in the world. It is a nocturnal sea star that was named from the venomous thorn-like spines that cover its body. They can be found in tropical coral reefs in the Red Sea, the Indian Ocean, and the Pacific Ocean.

• Read more in Marine Biology

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  Pincushion sea star—they live in tropical oceans. The species Culcita schmideliana has patches of different colors and doesn’t have any limbs.

*All images via Wikimedia Creative Commons Attribution ShareAlike 3.0

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