Supplanaxis nucleus, common name the black Atlantic planaxis, is a species of small sea snail, a marine gastropod mollusk in the family Planaxidae.

[1] This species occurs in the Caribbean Sea, the Gulf of Mexico and off the Lesser Antilles.

The maximum recorded shell length is 17 mm.

[2] Minimum recorded depth is 0 m.[2] Maximum recorded depth is 3 m.[2]

This Planaxidae-related article is a stub.