Moon Germ

The Moon Germs are a unicellular prokariotic species which parasitically inhabits Luna.

Biology
Despite looking like dog-sized spiders, they would be more accurately described as bacteria in the biological sense, and possess non-chromosomal DNA. They're also known for their hostility, as they're prone to attack people who encounter them.

Appearances

 * Doctor Who, series 8, ep.07 - "Kill the Moon" (2014)