Betelgeusian (The Hitchhiker's Guide to the Galaxy)

Betelgeusians are a humanoid species native to the Betelgeuse planetary system, and known to inhabit at least two of the system's planets: Betelgeuse V and VII.

Biology
Betelgeusians have strange familial structures, including multiple mothers and some sort of relation known as semi-cousin. They are able to grow extra arms and heads, although this might be due to medical intervention, more than a natural ability.

History
Current galactic president Zaphod Beeblebrox belongs to this species, and so does his semi-cousin Ford Prefect.