The Gelloids were a species, composed largely of protoplasm. They were known to the Federation by the 2370s.

A Gelloid was visiting Deep Space 9 in 2370 when the station became home to a disorientated group of Horta. When the Horta found their way onto the space station's promenade the people of the station, including the Gelloid and an avian trader, were rather startled and in the ensuing chaos the avian’s talons got stuck in the Gelloid's gooey protoplasm. (DS9 novel: Devil in the Sky)

The Gelloids were likely a species native the alpha or beta quadrants, though it's possible they were visiting gamma quadrant natives.