Crystoids seem to be radioactive, and try and exterminate anything that is not a Typhon based organism. It's also shown, that their nests are also sentient, but die when giving birth to these crystoids. They stay close, and are easily distracted.
Cystoids are the smallest Typhon creatures that players encounter in Prey, but their size can be deceptively disarming. About the size of a softball, these creatures make up for their diminutive size with some explosive firepower, and these little firecrackers tend to travel in packs and live in Cystoid Nests. Cystoids aren’t deep thinkers, so the second they sense movement, they take off on a Kamikaze mission that ends in a tiny explosion.
Being damaged by Cystoids gives radiation poisoning. The more Cystoids damages you, the more radiation poisoning you will take.
Cystoids look like small, black balls with spikes on them.
Cystoids kill themselves when they explode, so as long as players are aware of their surroundings, they can easily deal with these nests by tossing a random object in their direction or use GLOO cannon. Explosive Canister is an effective object to destroy multiple Cystoid.
Cystoids also produced by Weavers when attacked.
All weapons except GLOO Cannon are not reccomended since you will waste more ammo than what you can expect. GLOO Cannon can destroy Cystoid in one precision shot. The only exception weapon aside of GLOO Cannon is Huntress Boltcaster where the Huntress ammo can be retrieved after use. The Cystoids "hunt" the shots, as they make noise, and will explode if hit by them directly.
Cystoid Nest usually emits small radiation compared to Cystoid. It is one way to detect their presence if the nests are still around you.
If you encounter Cystoid Nest, it's better to find object that was large or having blast radius large enough to make a chain explosive which can also kill Cystoid upon impact such as Explosive Canister.
Be careful though that if you got attacked by multiple Cystoid at the same time, the radiation poisoning can even more lethal rather than one Cystoid at the time.