Space barnacle

Space barnacles, sometimes capitalised as Space Barnacles, were a space-borne, barnacle-like species that fed off energy and converted it into mass, in order to reproduce. They often clung to the outside of spacecraft, which provided them with a steady supply of energy to feed on. They looked like white, ridged domes.

History
Some space barnacles once attached themselves to the Godspeed, and started taking its power. They killed Tobbs when he tried to investigate. The Ninth Doctor told the crew to shut down all systems, materialised outside the Godspeed and used the light on top of the TARDIS to attract the barnacles. When they all moved to the TARDIS, he dematerialised, taking the sphere of barnacles with him, and rematerialised in a nearby asteroid belt where the barnacles could feed off the sun. (PROSE: The Hungry Night)

In November 2019, a "herd" of Space Barnacles ended up on Earth after coming through a Space-Time Rift. The Preternatural Research Bureau helped corral them back into the Rift so that the Space Lords' Space-Time Police could take custody of them. Maxie Masters was instructed to help P.R.O.B.E. to hunt down the space barnacles, which she didn't think was an exciting use of her time. (PROSE: Out of the Box)