Monday, August 17, 2009
Starfish, also known as sea stars, can be divided into two classes: Asteroidea (sea stars) and Ophiuroidea(brittle stars). The type you are probably most familiar with, which are the kind with 5 legs, are probably the Cushion Star, Sugar Star, and the North Atlantic Common Star which are all part of the Asteroidea family. However, there are several asteroidea which have more than 5 legs (see Sunflower Star and Millipede Starfish). The Ophiuroidea family includes some starfish you may never have heard of : the Basket Star and the Brittle Star. Unfortunately, I can't find any non-copyrighted photos of these stars right now to show you, but take my word for it, they're worth checking out.
Starfish do not have skeletons for moving and body support. Instead they use a water vascular system. Sea stars have two stomachs: one is used for digestion and the other is used as a mouth to engulf and begin digesting prey. Yes, this stomach can actually come outside of their bodies to grab food! This ability allows them to eat much larger prey than you might think. Starfish can easily prey on clams, oysters, small fish and mollusks. Like the sand dollar, a starfish's mouth is on the underside of its body.
Starfish are able to regenerate limbs. Most sea stars have 5 limbs, but some have more or less even within the same species. At the end of each limb or arm is a microscopic eye which allows the starfish to see light and dark. This doesn't give the starfish a very detailed view of its surroundings but this allows it to see movement which is used for hunting prey. All around the spines on the back of a starfish are small white objects called pedicellariae. These pedicellariae prevent encrusting organisms from living on the sea star.