Megalancistrus species are large and spiny and generally have 10dorsal-fin rays. The color on the sides and the abdomen is dark brown with very large spots on the head, sides, and fins or with light vermicualtions. The abdomen is completelyplated in adults. The caudal fin is forked, but without filaments. Cheekodontodes, as in Acanthicus, are thin but numerous. The plates on the body are well keeled with rows of odontodes above and below the keel rows incomplete in specimens up to at least.