Most urchins are grazers, scraping animal and plant material off surfaces as they move slowly along. Algae, bryozoans, sponges, and even sea cucumbers may be food to an urchin. A complex jaw apparatus called the Aristotle's lantern allows grazing urchins to eat just about anything. The lantern contains five teeth which are used for chewing, but can also be pushed out through the mouth for scraping. Feeding by urchins makes a star-shaped imprint from the lantern. When fossilized, the imprint leaves a record of urchin activity that can be interpreted by paleontologists. Some urchins, such as sand dollars and heart urchins, have evolved to burrow. While grazing urchins tend to have sharp spines that protect them from predators as they move along the seabed, burrowing urchins do not. Some burrowers lack the Aristotle's lantern, but others use the lantern and strong teeth to crush and ingest sand grains.