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

[1] It is known from specimens found in the Turvo State Park in Brazil.

[2] Cratera obsidiana is a flatworm that can reach up to 40 mm in length.

[2] Aside from its coloration, it is distinguished from other members of Cratera by having a posteriorly-shifted cylindrical pharynx and an extrabulbar prostatic vesicle with a T-shaped, dorsally oriented proximal portion.

[2] The specific epithet is derived from the volcanic rock obsidian, as the glossy black color of the species resembles that of the stone.