Onchidium luteum Semper, 1880 Platevindex luteus is a species of air-breathing sea slug, a shell-less marine pulmonate gastropod mollusk in the family Onchidiidae.

Its dorsal colouration is typically on a range between brown and nearly black, though yellowish-brown slugs have been found.

Its ventral side, however, ranges from dark blue to grey to white.

The eyes can be distributed across the entire notum, though they are not present at the edges of the mantle.

Typically, it is found on dead logs or on tree trunks, though some specimens have been found on tree roots, under loose bark, under rocks, on pieces of wood and plant material, and in dark mud.