Starfish typically reside in shallow waters along rocky coasts, according to The Columbia Encyclopedia. The starfish is an echinoderm of the Asteroidae class. Around 2,000 species of starfish exist across the planet.
Starfish range in size from around 1/2 inch to 3 feet in diameter and typically have five arms, although some species have up to 25. The echinoderms have a carnivorous diet made up mostly of bivalves, such as oysters and clams. As a result, starfish are a danger to commercial oyster beds. Starfish, also called sea stars, are distinguished from brittlestars, which have longer, jointed, more slender arms. Brittlestars are of another echinoderm class and live in deeper waters.