Monaxi

The  were a "trader" species which sold "lesser" species as slaves to "more developed" civilisations. (COMIC: Medicine Man)

The Monaxi worked with Mister Ebonite to capture individuals and put them in the Arena of Fear. (COMIC: Arena of Fear)

Biology
The Monaxi were a composite of matter and energy. They looked like ornate flying saucers. But this was just a protective shell. Their true form was a grotesque head with small eyes, a large mouth with serrated teeth, and a large number of tendrils under their head. Their entire body was enveloped by an energy carapace. This could, however, be penetrated by a sonic screwdriver. The resulting shock would stun a Monaxi. (COMIC: Medicine Man)

Culture
The Monaxi were a race of slavers who used Earth and a number of other "primitive" worlds as hunting grounds where they would capture potential slaves and sell them to "higher species". The Monaxi looked down on all bipeds such as humans or Time Lords who all looked the same to them. (COMIC: Medicine Man)