The Remoraxians were a species of "interstellar parasites", also known as "space remora" in some parts of the Milky Way. Their modus operandi was to travel from system to system, constantly looking for a new home to convert in a suitable habitat for them, namely a waterworld.
They were led by the Remoraxian Prime, their genetic monarch, who could command them in different forms.
They were known humanoid forms and smaller parasite ones (in the strict sense of the word), able to take over the will of other beings. They were all provided with sharp teeth.
In 1974, the Remoraxian tried to invade and occupy Earth, by flooding it through artificial climatic changes. The Brigadier and other UNIT members were possessed by some Remoraxians set in their throats. Thanks to the Third Doctor, they were freed and the whole fleet was compelled to leave the planet. (COMIC: In With the Tide)