The
Matrium!
It is a type of spreading fungus that can only spread in the dark. This way, it would only exist in ships (In places were lighting isn't high) and in caves. Direct sunlight would damage it. However, if it is a player made light, its spread would decrease extremely, but could cover up the light. To defend its new growth, it could then make a few "Pods", that create a few creatures when a player comes near. Pods would probably come from advanced/less used blocks like bobby AI and computers. This would also give something for the Human NPCs to do. You could use them to defend your ship from these little buggers. The way they would spread from ships however, is that if there is over 360 "infected" blocks, then these mega spore cannons could start forming. These Spore Cannons would look like a Spore Cannon from the Zerg, in Starcraft. If a ship comes into range, it would fire from a special block called a BioMass Computer. You could basically make a biological weapon by harvesting from the spores, infesting a part of your ship on purpose to send into your enemies.
Blocks:
Mycelium Vines - 6hp 1 armor - grows on walls. Blocks with Vines on them turn into Plagued Blocks.
Plagued Blocks - 120hp 80 armor - Is turned into by Vines. Powerful and hard to get rid of. Can spawn Emitters on them.
Emitters - 18 hp 5 armor - Makes the nearby 8x8x8 "air" blocks nearby into damaging effects. They are quite rare and only spawn in deeply infected areas.
Spawner - 22 hp 12 armor - Spawns mobile spores. Only spawns when a player is nearby.
Basicly, they are slow growing infections fungus. They grow so slowly, a server would have to be on 24/7 for the fungus to take control of a ship.
Who knows, maybe players will begin to make temples in their name
