Marsenina stearnsii is a species of small slug-like sea snail, a marine gastropod mollusc in the family Velutinidae.

The thin, translucent white shell is visible through a dorsal pore in the mantle.

The finely pitted mantle is white to pale pink with darker spots.

[citation needed] This white slug-like snail is known from Alaska[3] and central California.

[4][5] It is relatively rare, found in the low rocky intertidal, usually under rocks on the ascidian Trididemnem opacum which it matches in color and pattern and upon which it preys.