Hypostomus basilisko is distinguished from all congeners, except those belonging to the H. cochliodon group, by having the following unique combination of characters: absence of notch between metapterygoid and hyomandibula(vs. presence of notch); and strongly angled dentaries, less than 80° (vs. shallow angle between dentaries, generally more

than 80°). It differs the other members of H. cochliodon group, except H. pagei and H. soniae, by the absence of spots on body and fins (vs. presence of spots). It is distinguished from H. pagei by having highly developed keels on lateral series of plates (vs. keels weak, almost absent); from H. soniae for having teeth with a large spoon-shaped mesial cusp and a lateral cusp, if present, almost imperceptible (vs. teeth with mesial cusp conspicuously enlarged and rounded but not spoon shaped; distinct lateral cusp) and massive odontodes covering the dorsal region of head and trunk, forming well-developed keels (vs. less developed odontodes on head and trunk, keels absent or

weakly-developed). It can be distinguished from H. soniae by the possession of many well-developed papilla on the internal surface of anterior and posterior jaws (vs. few papillae on the internal surface of anterior and posterior jaws); from H. cochliodon and H. khimaeraby having 27 vertebrae (29 and 28, respectively); from H. hondae (Regan) and H. plecostomoides (Eigenmann) by the absence of platelets in the skin around dorsal-fin base (vs. presence); from H. levis by the presence of an adipose fin (vs. absence); from H. taphorni by having both caudal-fin lobes evenly colored (vs. bicolored caudal fin with ventral lobe darker) (Ref. 97225).