Marionia gemmii is a species of sea slug, a dendronotid nudibranch, a marine gastropod mollusc in the family Tritoniidae.

[2] This species was described from the Ria de Arousa, NW Spain, 42°30′21″N 8°56′05″W / 42.5057°N 8.9347°W / 42.5057; -8.9347.

[1] It has been reported from the Mediterranean Sea.

[3][4]