Cratera tui is a species of land planarian belonging to the subfamily Geoplaninae.

The dorsal side of the body has a melon yellow median stripe that is bordered on both sides by a jet black stripe.

The front of the body fades into a carmine red color.

[2] Aside from its coloration and length, it is distinguished from other members of Cratera by having marginal eyes, a cylindrical pharynx, a pharyngeal pouch that is 0.6 mm anterior to the prostatic vesicle, a penis papilla that is shorter than the male atrium, a relatively small distal dilation of the ejaculatory duct, a female atrium that is 2.5 times longer than the male, and the presence of a long common glandular ovovitelline duct.

[2] The specific epithet is derived from the Tupi language word tui, "tiny, insignificant", in reference to the small size of the ejaculatory duct's distal dilation.