The family Urolophidae, also known as stingarees, consists of two genera and about 35 species. They are bottom-dwelling rays in warm seas, usually lying partially buried under the sand. Their rounded pectoral discs are colored to blend in with the sand, mud, or rocks on which they live. Urolophids are relatively small rays, and feed on a variety of invertebrates, small fishes, and crustaceans. Their tails, distinguished by the presence of a well-developed caudal fin, are equipped with one or more serrated stinging spines. Like other rays they are viviparous; urolophids give birth to between two and four young each year, or in some cases, every two years. Because of their low birth rates and sometimes restricted range, urolophids are susceptible to human activity, although only one species is currently known to be threatened.