The Echinoid Directory


Heart urchins are covered in a dense coating of hair-like spines which typically end in a small spatulate tip. These spines serve a number of functions. On the aboral surface they help compact the burrow walls and maintain a sediment-free space around the animal. The spines on the lower surface are used for burrowing and for forward propulsion. The spines around the anterior margin are used to excavate sediment as the animal moves forward. The petals are roofed by an arch of spines, creating a large water-filled space for respiration. In many taxa specialised small and densely packed spines with mucous tips form distinct bands termed fascioles. On the bare test these appear as lines of close-packed granules.