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. 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 (see picture). They are water-dwelling organisms by nature, but by the means of their alien technology they are able to move about on land. They have no lungs, only gills, so they must carry a supply of water along with them while on land, or they will suffocate within minutes.
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. 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. 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.