Organoids
Organoids are a special type of Zoid left over from the time of the Ancient Zoidians. They usually look like small Tyrannosaurs, (albeit many with added features like wings, spikes, etc.), and are around the size of a small horse. Organoids are unique to Chaotic Century and Guardian Force, and do not appear in any other series (though they appear in some games). Organoids have the ability to fuse with other Zoids, either healing them, making them more powerful, evolving them, etc. They also have the memories of their Zoidian partners stored inside of them. Only four Organoids appear in the series: Zeke, Shadow, Ambient, and Specula.
Read more about this topic: Zoids: Chaotic Century