Several species have specialized feeding behaviours including eversion of their stomachs and suspension feeding.They have complex life cycles and can reproduce both sexually and asexually.
Starfish, such as the ochre sea star (Pisaster ochraceus) and the reef sea star (Stichaster australis), have become widely known as examples of the keystone species concept in ecology.
The tropical crown-of-thorns starfish (Acanthaster planci) is a voracious predator of coral throughout the Indo-Pacific region, and the northern Pacific sea star is considered to be one of the world's 100 worst invasive species.
The fossil record for starfish is ancient, dating back to the Ordovician around 450 million years ago, but it is rather poor, as starfish tend to disintegrate after death.
Only the ossicles and spines of the animal are likely to be preserved, making remains hard to locate.
With their appealing symmetrical shape, starfish have played a part in literature, legend, design and popular culture.
They are sometimes collected as curios, used in design or as logos, and in some cultures, despite possible toxicity, they are eaten.
The class Asteroidea belongs to the phylum Echinodermata.
As well as the starfish, the echinoderms include sea urchins, sand dollars, brittle and basket stars, sea cucumbers and crinoids.
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea.
Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or "basket stars".
About 1,500 species of starfish occur on the seabed in all the world's oceans, from the tropics to frigid polar waters.