Catfish (order Siluriformes) are a very diverse group of bony fish. Named for their prominent barbels, which give the image of cat-like whiskers, catfish range in size and behavior from the heaviest, the Mekong giant catfish in Southeast Asia and the longest, the wels catfish of Eurasia, to detritivores (species that eat dead material on the bottom), and even to a tiny parasitic species commonly called the candiru, Vandellia cirrhosa. There are armour-plated types and also naked types, neither having scales. Despite their common name, not all catfish have prominent barbels; what defines a fish as being in the order Siluriformes are in fact certain features of the skull and swimbladder. Catfish are of considerable commercial importance; many of the larger species are farmed or fished for food, and some are exploited for sport fishing, including a kind known as noodling. Many of the smaller species, particularly the genus Corydoras, are important in the aquarium hobby.