Echinaster sentus (Say, 1825) - live spiny starfish (oral view) in Florida, USA (December 2012).

Starfish are vagrant, benthic, mostly predatory echinoderms. They have a multielement skeleton composed of numerous, small, calcitic plates. Most starfish are pentaradial (they have 5 arms), but some species have 6 or more arms. Many starfish are predators, although some can deposit feed. Predatory starfish include forms that consume prey, usually bivalves, by everting their stomachs through their mouths (= centrally located on the underside) and digest food externally.

The above photo shows the oral side ("underside") of a live spiny starfish, Echinaster sentus. The groove at the center of each of the five arms is an ambulacrum. Each ambulacral groove is lined with numerous small tube feet that the starfish uses for locomotion and to move food to the mouth, which is located at the center of the five arms.

Classification: Animalia, Echinodermata, Asteroidea, Spinulosida, Echinasteridae

Locality: just offshore from Bird Key Middle Ground East Beach (Main Channel North Beach; Cabbage Key-Pine Key North Beach) - marine shoreline on the eastern side of Rt. 679, just north of Cabbage Key & Pine Key, northern side of Tampa Bay, south of the city of St. Petersburg, Gulf of Mexico coast of southern Florida, USA

More info. at: en.wikipedia.org/wiki/Starfish and gcrothmarinestation.wikispaces.com/E and