Starfishes, or sea stars, are members of the do-all-starfishes-or-sea-stars-have-five-armsAsteroidea. Their bodies consist of a central disk from which radiate from five to more than twenty arms or rays

Seastars, sea urchins, and sea cucumbers are all members of the phylum Echinodermata.

Other members of this phylum include: sand dollars, brittle stars, basket stars, feather stars, sea lilies, and heart urchins.

If your asking where it is, its on the Ventral(bottom) side. It is the indent in the starfishes' skin that goes through all of the starfishes' rays (arms). It is called the ambulacral groove.

Sea Stars and starfish, one in the same, are echinoderms. There are over 1500 varieties, but they all share the five point 'star' shape which consists of a central disc with five arms.

at the bottom of the sea and ocean