Hydrans were a non-humanoid species. Their government was the Hydran Kingdom. (Star Fleet Battles, Star Trek: Origins, RIS Bouteina: "Humans, Romulans and Space-Beasts")
Biology[]
Hydrans were notable to breathe methane, which could be uncomfortable or lethal for most Federation species. They had three arms, legs and eyes, as well as a tough, leathery skin. They had three sexes: male, female and matriarchal, only two of which are sentient. All births resulted in multiples of 3 (at least one of each sex) who are taken care of by the Matriarchals. (TOS games: Starfleet Command (game), Starfleet Command Volume II: Empires at War)
Hydran romance levels were determined by their levels of manethozine, which was detectable by a love tester. (RIS Bouteina: "Love Plan")
Culture[]
Males tended to dominate command-level positions, as well as science and engineering, while females tend to form up most of the worker classes, as well as marines and fighter pilots. Some females could hold command positions (usually within fighter squadrons), or even the throne. Matriarchals were non-sentient and were homemakers.
Their culture was deeply religious and their religion bordered on animism, as each household, starship, squadron and fleet possessed a god or a set of gods. Some gods were of a higher order, but what gods were put in the public limelight were decided by what groups came to power. Even with Hydran religion, the Hydrans were similar in disposition to the Federation concerning diplomacy and exploration so that, when they weren't at war, they were out there exploring the galaxy for scientific purposes.
Hydrans tended to favor sending fighters as a first line and then let the mothership close in on the target. (TOS games: Starfleet Command (game), Starfleet Command Volume II: Empires at War)
Technology[]
Hydran warships usually came in three flavors: fusion beam-armed carriers for close combat, hellbore cannon-armed ships for long-ranged combat and orbital bombardment and, finally, command cruisers as well as explorers with mixed weaponry. Also, Hydrans were among the first to develop ablative armor and Hydran ships were usually built to last a long time, if not for combat. They also designed their ships for continuous operation under maximum evacuation capacity. Its shipbuilding culture was also marked by a never-ending desire of greater MEC per unit of mass. (RIS Bouteina: "Fury of the Prison Ships")
Also, Hydran replicators were usually networked in a ship so that all replicators could serve the same things. (RIS Bouteina: "Spoiled Rotten")
Finally, gatling phasers were standard equipment on Hydran starships by the late 24th century. (RIS Bouteina: "Hystelic Kingdom")
They were able to break the time barrier before the Federation and the Klingons were able to develop the hardware necessary. (Star Trek: Origins)