What is a sea star?
There are more than 1,800 species of sea stars, which all belong to the phylum Echinodermata (along with brittle stars, sea urchins, sand dollars and sea cucumbers). Members of the class Asteroidea, sea stars have spiny skin imbedded with calcareous (or calcium carbonate) plates, which create a somewhat rigid exo-skeleton that allows for some movement. Most species have five rays, but some have many more, all radiating from a single disc in the animals center. The largest collected in the North Pacific measure more than 40 inches in diameter, while the smallest is the size of a quarter. Sea stars have an amazing ability to regenerate lost rays; in some species, whole sea stars can grow from a single ray that has retained a portion of its central disc. Sea stars dont see in the conventional sense. Theres a small red pigment spot at the end of each ray, which is sensitive to light, so the sea star knows when it is moving into dark crevices, or whether another creature has passed before i
