Starfish Family: Stelleroidea (PA-24)
Stelleroidea are stemless
echinoderms that have a central disc from which five or more arms radiate.
It includes the true starfish (Asteroidea), the brittle or serpent stars
(Ophiuroidea), and the somasters (Somasteroidea). They appeared in
Ordovician seas more than 450 million years ago. They are thought to be
descended from unknown crinoids that lost their stalks but quickly
developed arms for more efficient locomotion and feeding. The asteroids
and ophiuroids have many living representatives; the somasters are nearly
Starfish live in the tidal zones and in the abyssal depths.
Some of their food is dead organisms, but they also eat small algae and
small invertebrates. Whole starfish fossils are rare, for they tend to
fall apart after death. Complete starfish have been found in Mississippian
siltstones in Montgomery County and also in Ordovician rocks in
Our Hoosier State Beneath Us: