Frequently found under rock or reef ledges.  Carnivorous with well-developed organs for scent and vibration detection.<P> Like all sharks, the nurse shark has a skeleton of cartilage rather than bone.  Instead of scales, its body is covered with tiny razor-sharp denticles.  The teeth are specialized forms of denticles.  Sharks must continually swim or will slowly sink because they have no air bladder.<P> Edibility is poor.<P> Range is from Rhode Island to Brazil, including the Gulf of Mexico.