Aquamen

The Aquamen were an enemy whom the Fourth Doctor recalled having defeated. (PROSE: The English Way of Death)

Behind the scenes
Among some 250,000 entries, the "Aqua Man", created by Stephen Thompson, was one of three winners of the Blue Peter's 1967 design-a-monster-competition, along with the Hypnotron and the Steel Octopus. Unlike the later Abzorbaloff, it was not featured in the Doctor Who television series, however, a prop Aqua Man was constructed alongside the Steel Octopus and the Hypnotron. (REF: The Doctors: The Archive)