The Prime Species are one of the most common species in the Yheyn-Seas. Across the Matoran Universe, there are six varieties. However, in the wake of the Leagues fall, their already tenuous relationships have all but fallen apart, and it's considered a crime against existance to be a member of one in territory that another shares.
The Southern Alliance, as its, has representatives of two species - those of Pridak and Carapar. Ehleks species once used to be very commonplace, but all but vanished a couple thousand years ago with no explanation.
Thus it is with Yheyn. The Prime Species have their own unique names, but they cannot be pronounced by any but those of that species, and only in the ancient languages members of that species once spoke in the past. Instead, most simply refer to them all as Primes, and let the universe sort the rest of it out in a conversation.
Pridaks species of Prime are of roughly the size of a Toa. Their armoring is generally red or white with a secondary color, thoguh there are a few exceptions. They are far more physically adept than the avreage Toa, being incredibly fast and possessing enhanced senses and strength.
Carapars species of Prime are much larger, standing only a head shorter than a Vortixx and being much bulkier overall. There armoring is often of a dark coloration, and is incredibly thick. They are much stronger and tougher than most species, though they are about equal with a Zyglak. Crossbows are commonly employed against them, as normal arrows simply break against their plated hides. They are also resistant to the environment around them.
Both species of Prime are naturally adept at using Kanohi powers, being quick to adapt to a new mask and able to use them at heightened levels of efficiency. Many are also natural leaders as well, and dislike having to follow others - thus, only highly charismatic individuals are able to gather large forces of Primes to their service for extended periods of time. The Barraki come to mind.