The presence of these traits in mature males cannot be confirmed in C. amphiloxa, C. caiapo, C. jurubidae, C. parma, due to the small number of specimens.

C. arcana, C. montana, C. pearsoni, C. sandrae, C. starnesi, and C. umbrosa have a posteriorly rounded, variably developed, bilobed patch of dark pigmentation at the base of the caudal fin.

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.

[2] C. arcana was collected in a karstic region of the upper Tocantins River basin in both epigean (above-ground) and subterranean waters.

Specimens were collected at depths of 2 m or less and at an elevation of less than 50 m.[1] C. motatanensis is found in swiftly flowing water among rubble to coarse gravel.

[1] C. orinoco reportedly inhabits the middle portions of the water column of high-velocity streams during the night and hides among submerged branches and other obstructions in the river channel during the day.

[1] C. sandrae was found in riffles in a relatively fast-flowing forest stream, approximately 3–4 m wide and 0.4–0.8 m deep with a small waterfall.

[1] C. candiru, commonly known as the Candiru-açu, is perhaps the most formidable species, being a hunter and scavenger of dead and dying fish, which it devours from the inside-out using its circular maw of razor-sharp teeth.

Featured heavily in River Monsters and BBC's "Amazon Abyss", it has been implicated and proven to attack and devour humans, with corpses containing hundreds of fish being recorded in morgues.