• Echinus is commonly known as Sea urchin.

• Body is globular in shape, somewhat flattened at the two poles forming distinct oral and aboral -poles.

• Body is enclosed in a rigid globular shell formed of closely fitted calcareous plates.

• Entire surface of the animal except the peristome and periproct is covered with spines articulated to the shell.

• Pedicellariae with three jaws and sphaeridia are present among the spines.