Marinian

The Marinians were a "human race," one of the "many races" of Marinus. Altos was a Marinian.

The territorial waters surrounding the island of the Great City were also referred to as "Marinian waters." (PROSE: Doctor Who and the Keys of Marinus)

Behind the scenes
It is uncertain whether the term "Marinian" refers to the species which would later be known as the Arbitan or if it is an umbrella term for the "many races of men" as mentioned by Yartek, a Voord. In the serial The Keys of Marinus a Voord was described as a "man" while in the novelisation the Voord were called "creatures" and "sub-humans."