Alien Races

HG Wells' Selenites and Martians could coexist. Some future history series have many alien species but maybe two main ones? Heinlein's Future History has two sets of two: Martians and Venerians in the Solar System and two extra-solar races.

Poul Anderson's Technic History: Ythrians; Merseians.

Larry Niven's Known Space: kzinti; Puppeteers.

Star Trek: Vulcans; Klingons.

Jerry Pournelle's CoDominium: Moties; -?

Kzinti, Vulcans and Klingons are multi-authored. Ythrians and kzinti have each been imported to another series.

Knowing, for example, that kzinti have a low tolerance for sensory deprivation, insightful authors can draw novel conclusions:

"The walls here in this section of officer country were covered with holographic murals; a necessity, since kzinti were very vulnerable to sensory deprivation."

-"The Man Who Would Be Kzin," p. 298.

Similarly, an Ythrian ship must have large portholes, a large chamber for flying and no spacesuits. That large chamber also provides a cabin of appropriate size for a Wodenite.

Back to those murals: one shows two kzinti burying their muzzles in the belly of a giant turtle, as if we needed to be reminded of either Ythrian or kzinti eating habits. See Hunting.