Space amoebae
Like common planetary amoebae, but instead of growing in the biosphere of a planet, the Space Amoebae have evolved in the hydrogen deposits of certain nebulae. This, in turn, has left no limitation like gravity to their form, and thus they can grow very large.
Biology
Under normal conditions the space amoebae graze on gases common to stellar nebulae.
All but the younger specimens are accompanied by quasi-independent flagella, organisms spawned by the Amoeba and programmed through liquid, RNA-laced secretions to do the bidding of its host. These flagella are capable of manipulating and even attacking objects in an impressive yet restricted range around the host, periodically returning to lodge inside the host Amoeba's body for re-programming.
They are not that dangerous to starships, as long as the vessels don't enter the mass of their bodies. When this happens, the situation can get bad - The sticky mucuslike substance they're made of can easily trap ships inside them, and especially shieldless craft with low-grade propulsion systems will have trouble shaking free.
Sometimes, the amoebae can also mistake the trapped vessels for nutritive substances and start digesting them. In this case, it is advisable to immediately contact local space authorities or other nearby vessels for help.
Images
Starship maneuvers for evading space amoebae, from an UOSF operations manual.
