The Echinoid Directory

Locomotion: burrowing

Many irregular echinoids burrow beneath the surface of the sea floor, like Echinocardium pictured below. Sand dollars and their relatives burrow by ploughing forward into the sediment at a shallow angle. In many heart urchins a different approach is used and sediment is excavated laterally from underneath the animal by oral spines. In this way the animal sinks vertically into the sediment. Once in the sediment, forward motion is achieved by using spines around the anterior margin to loosen and excavate grains from the front wall while strong spines on the posterior part of the oral surface (the plastron) provide powerful forward thrust. Heart urchins move forward through the sediment at one or two centimetres an hour. The walls of the burrow are maintained by aboral spines, which are often curved and hair-like to provide a dense and effective canopy.