Venerian

Venerians are a sapient, non-spacefaring species of aquatic creatures which inhabit the anoxic oceans of Venus, hundreds of millions of years after the extinction of the First Men. They were rendered extinct when their planet was terraformed by Earth colonists.

Biology
Venerians physically resemble swordfish in both size and shape, but also possess three retractable clawed tentacles hidden within the "sword", which can be extended and used as manipulatory appendages. They have three steering fins and three tails, and rotate their bodies in a screw-like motion while swimming. They have organs specialized for luminescence, and their senses include sight, touch and "something analogous to hearing". They communicate by snapping the crab-like claws at the end of their tentacles.

The Venusian food chain is based on the energy generated from natural sources of radioactivity, rather than photosynthesis. The Venerians reproduce asexually by laying eggs on the seafloor. Before completing their maturation into adulthood, they gather enough radioactive matter to keep them alive for several years, so that, as adults, they don't ordinarily need to feed. When they run out of food, they are either killed or burrowed in radioactive deposits to be rejuvenated.

Having evolved in an anoxic world, free oxygen is lethal to the Venerians. Being accustomed to the oceanic depths, they can't rise to the surface, as the difference in pressure would burst them.

Culture and society
The Venerians inhabit cities made of coral-like buildings on the oceanic floor. Their culture is belligerent and materialistic.

Appearances

 * Last and First Men: A Story of the Near and Far Future, by Olaf Stapledon (1930)