Achirus mucuri is distinguished from all its congeners, except A. novoae, by

possessing a connection on both the blind and ocular sides between the branchiostegal membrane and the isthmus, with the connection being slightly stronger on the blind side (vs. complete absence of connections between branchiostegal membranes and isthmus). Additionally, the species is distinguished from its congeners by having a light-brown body color, with regularly-scattered, minute, darkbrown blotches that are sometimes concentrated to form larger spots. Five specimens differed from the typical light-brown body color in having a brownish-gray background, and one specimen showed brownish-white body pigmentation. The new species differs from A. novoae by the presence of a large, ramified labial fimbriae (vs. simple, non-ramified, minute labial fimbriae in A. novoae) and by the shape of the infraorbital canal (extending around ventral margin of fixed eye) (vs. infraorbital canal that

stops dorsal to fixed eye in A. novoae (Ref. 80995).