Hydras are the massive 50 foot worms deployed by The Zodiac to purify defiant Zodiac Rebel worlds. They are born to serve and are deployed more like equipment than soldiers. Named because of the way they spew out a plasma mortor which, when shot, splits into 2, and those each split into 2, and so forth and so on. Hydra names aren't as readily known as the rest. They seem to all start with "R" and end with "L", ex: Rigel, Razzal, Reynell, Rethenelliel, it seems to be a common.