Nurse sharks are nocturnal and will often rest on the sea floor during the day in groups of up to 40 sharks, sometimes piled on top of each other. The scientific name Ginglymostoma cirratum is is a mix of Greek and Latin and means "curled, hinged mouth" to describe this shark's somewhat puckered appearance. The origin of the name "nurse shark" is unclear. It may come from the sucking sound they make when hunting for prey in the sand, which vaguely resembles that of a nursing baby. Or it may derive from an archaic word, nusse, meaning cat shark. The most likely theory though is that the name comes from the Old English word for sea-floor shark: horse. Nurse sharks are slow-moving bottom-dwellers and are, for the most part, harmless to humans. However, they can be huge—up to 14 feet (4.3 meters)—and have very strong jaws filled with thousands of tiny, serrated teeth, and will bite defensively if stepped on or bothered by divers who assume they’re docile. They use their strong jaws to crush and eat shellfish and even coral, but prefer to dine on fish, shrimp, and squid. They are gray-brown and have distinctive tail fins that can be up to one-fourth their total length. Unlike most other sharks, nurses are smooth to the touch. Overall brown or deep rust color. It has a very small, underslung mouth, and is our only Shark with barbels at the nostrils. Dorsal spines (total): 0. Moderately long barbels, nasoral grooves present but no perinasal grooves, mouth well in front of eyes, spiracles minute, precaudal tail shorter than head and body, dorsal fins broadly rounded (the first much larger than the second and anal fins), caudal fin moderately long, over 1/4 of total length, yellow-brown to grey-brown in color, with or without small dark spots and obscure dorsal saddle markings. Head blunt, mouth inferior, pair of conspicuous barbels between nostrils