Saharduin
One of the most enduring, lasting and popular races in Warhammer 40,000, /tg/ loves the Sarhaduin.
The Saharduin (sometimes known as "Piscean Warriors") are a race of shark-like aliens. They should not be confused with the Space Marine chapter the Space Sharks, who cry themselves to sleep at night, wishing they where as awesome as the Saharduin.
Sarharduins possess a sinuous body, with a long, finned tail. They have two legs and two arms, and a mouthful of sharp teeth. They stand approximately seven and a half feet tall in their typical stance. They are water-dwelling organisms by nature, but solve this by having a tank of water on their back and reproductive organs made of the strongest steel.
The Saharduin control several worlds in the Ultima Segmentum. They are both hostile and powerful, and have technology roughly equivalent to that of the Imperium, but wetter. A typical Piscean Warrior is armed with a boltgun-analogue and a power sword. The Imperium fought a long war against the Sarharduin, but were unable to eradicate them, though this may simply be because the Ultramarines are rubbish. The menace could only be contained. To this day, no known human has ever set foot upon one of the planets of Saharduin; they remain dark and unexplored.