Alopia nefasta is a species of small, tropical, air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Clausiliidae.

Its color ranges from brown-violet to dull blue, with a more prominent white suture thread and a yellowish-white, slightly bulging area behind the aperture.

The sculpture is similar to the typical form and consists primarily of more or less distinct growth lines, but can vary among specimens.

It may range from clear ribbed lines to dense, even, and fairly sharp ridges, which either match the shell's color or appear lighter, sometimes even white.

In some specimens, the lower lamella becomes faintly visible in the aperture; otherwise, the remaining features are consistent with the typical form.