They were headed toward the United Federation of Planets, dominating all species in their path. Their arrival was estimated in the 33rd century, give or take a century. They are like the Arivne, as they were telepathic, but were also emotional and belligerent.
They were about the size of a horse and look like a cross between an insect and a centaur. They had four legs with three joints covered in shiny black chitin. Their egg-shaped bodies were shiny brown with bits of green and blue. The thorax, rising from the front, had black bristles, two arms, and a head. The arms were mechanical looking, ending in tentacles with one arm bigger than the other. Each of the four elbows had a hooked claw. The head was triangular with bubbly red eyes that looked like two clusters of salmon eggs and a small hole for a mouth. The mouth had a slender black tongue that went in and out, and finished off their bodies with a thick, barbed scorpion-like tail.
The life span of some Irapina was as long as two thousand years. This group harvested organs from other Irapina for use as replacement parts.
By the 23rd century their invasion force consisted of ten billion of the ruling class. They had four planet-sized Irapina starships approximately twenty-five thousand light years away from Federation space. They were moving quite slow, at approximately warp three.
Circa 2230, the Irapina detect two powerful psychokinetic and telepathic races in the vicinity of the Federation, the Arivne and the Organians. They began to consider transporting advanced scouts to test the mental determination of future enemies, though the energy expenditure would delay their fleet's arrival until the 34th century.
In 2269 the Irapina decided to send representatives to Organia and the Arivne homeworld of Anomaly. The Arivne acted as intermediaries and translators so that the Irapina could interact with Federation representatives within interactive, illusory tests. James T. Kirk, Spock and Leonard McCoy subsequently engaged the Irapina. At last report, the Irapina were frightened into changing course. Their new heading was the Orion Arm of the galaxy, for the Romulan Star Empire. (TOS novel: Planet of Judgment)