• Phylum: Echinodermes
• Class:
• Common name: Sea stars, Starfish, Asteroids
• Scientific name: Asteroidea

Asteroids represent one of the best-known classes of echinoderms. In fact, if I tell you that asteroids are simply starfish, you’ll immediately recognize them.

Starfish include more than 1,600 species.

Starfish can reach over 3 feet across when their arms are fully extended.

Starfish usually have 5 arms or a multiple of 5. This number can change during their lifetime if, after the loss of an arm, regeneration produces two new arms instead of one.

The skeleton of a starfish is made of calcareous plates that are adjacent but not fused together.

To move around, a starfish uses an ambulacral system made up of two types of tube feet:

• with suction cups for hard substrates
• without suction cups for soft substrates

Starfish are found at all latitudes and at all depths, from the surface waters down to the deep sea.

To feed, starfish use a truly unique digestive strategy. They can evert their stomach, meaning they push it outside their body, directly onto their prey. This allows them to secrete digestive enzymes that begin breaking down the tissues of the captured animal, most often bivalve mollusks such as mussels or scallops. Once the flesh is softened and partially digested, the starfish retracts its stomach back into its body to complete digestion and absorb nutrients. This ingenious mechanism enables them to consume prey larger than their mouth might suggest.

Starfish have one pair of gonads in each arm. However, it is very difficult to determine the sex of a starfish.

Starfish can also reproduce asexually by splitting off part of the central disc along with one arm, then regenerating the missing arms.

Starfish have phenomenal strength: using their powerful tube feet equipped with suction cups, they are capable of prying open the shells of a bivalves such as a great Atlantic scallop.

The crown-of-thorns starfish (Acanthaster planci) is responsible for major damage to coral reefs, which it feeds on voraciously.

Starfish can also cause serious damage in mussel farms.