The Echinoid Directory


Spines are made of calcite and are used by regular echinoids for defence and locomotion. Each spine articulates to a tubercle on the test. In the cidarid pictured below there are large primary spines (white) and a mass of smaller secondary spines around their bases. Cidarids are unusual in having an outer layer of calcite, the cortex, which rapidly becomes covered in algae and provides camouflage for the animal. In all other echinoids there is a living skin covering the spines and spines never become encrusted. Spines are bound to the test by soft tissue and so are readily lost after death and are rarely preserved in life position in fossils.

Spines come in a wide range of shapes and sizes (see below). The spines of Diadema (middle left) are long and needle-like and used primarily to ward off predators. In Podophora (far right) the aboral spines are modified to form a tessellated canopy, an adaptation for life in the very high-energy rocky-shore environments. Some cidaroids evolved large glandiform spines.

Spine structure is variable and provides important taxonomic characters. The shaft can be smooth or ornamented by ribs, thorns or granules. In cross-section it may be hollow or solid.