These fish have a skeleton consisting of cartilage rather than bone, they lack scales and the body is covered in a tough skin that has a rough surface due to the numerous small teeth called 'denticles' embedded in it. Most species have 5 gill slits on each side of the body; a few species have 6 or 7 pairs of gill slits. They are all carnivorous, eating a range of live or dead vertebrate and invertebrate animals. Most species bear live young, whereas a few species produce eggs sealed in egg cases that are attached to algae or to the seabed. Rays have a flattened, round or diamond-shaped body and a long, thin tail with one or two venomous spines.