The body of "Cetopsis" species ranges from slender to stout. Unlike all other species, "C. candiru" has incisiform (vs. conical) teeth on the vomer and dentary, and also has a more slender body than all other species. Unlike all other species, "C. coecutiens" has transverse, slit-like posterior nares rather than rounded posterior nares. The eye is completely absent in "C. oliveirai"; the eye, present to some degree in all other species of "Cetopsis", is situated on the lateral surface of the head and is visible from above but not below. In most species, the mouth is inferior and the width is one-half the length of the head; the margin of the lower jaw is often gently to broadly rounded. The mental barbels are almost always approximately the same size and length to each other and often the same length as or sometimes shorter than the slender and short maxillary barbels. In most species, the dorsal fin is moderately large, but in "C. caiapo" and "C. parma", it is relatively small. The caudal fin is shallowly to deeply forked and symmetrical (though apparently asymmetrical in "C. jurubidae"), the ends of the lobes usually pointed, bluntly pointed, or rounded (however, the tips are damaged in the single specimen of "C. umbrosa"). The base of the anal fin is moderate to long, though is relatively short in some species. The pelvic fin ranges from short to moderate to large. The pectoral fin length is usually two-thirds of the length of the head.