The Mermen, with the singular form being Merman, were a race of long-gone creatures from the watery depths of Mon Calamari, found in the ocean. These green-skinned entities possessed legs that merged into a tail resembling that of a fish.
On Coruscant, the Holographic Zoo of Extinct Animals featured a holographic display showcasing Mermen in the act of hunting a krabbex. They were depicted wielding spears crafted from bone.
As indicated in Star Wars (1977) 75, beings referred to as Mermen seemingly existed on the planet Iskalon when the Iskalon Effect occurred, resulting in the deaths of numerous innocent mermen due to the resulting massive wave. It is possible, however, that the term "mermen" was simply another name for the native Iskalonians.