STAR WHALE

The Star Whales are ancient giant peaceful spacebound sentient creatures. They had several flippers and tentacle like protrusions on their backs and are capable of surviving in the vacuum of space. According to legend, they guided early space travellers through dangers on their journeys through space. By the 29th century, the species is believed extinct save for one, who is theorised to be the last of its kind.
Source: Doctor Who Universe, DW: The Beast Below

MULTI-FORM SPECIES

The multi-form species is a sentient lifeform naturally gelatinous, appearing as a snakelike mass of glowing tendrils with a mouth full of sharp teeth. Capable of creating a perception filter to stop itself being seen, or to hide anything it wants to hide, it is highly polymorph. Having created a psychic link to a living but dormant creature, it can then copy the appearance of that creature or of anything they dream about. Coma patients provide the perfect live feed. They can live for millenia.

One specimen of the species, Prisonner Zero, a known galactic criminal, was locked up in an interdimensionnal prison on Earth by the Atrax for years until 2010.

Source: Doctor Who Universe, DW: The Eleventh Hour

ATRAXI

The Atraxi are a galactic police force.
Working in groups, they resemble eyeballs four meters in diameter around which orbits a ring-like crystalline snowflake structure.
They are capable of atmosheric as well as of interstellar flight. They can perform planetary scanning tasks in a 'searchlight' fashion and lock a planet inside a force field inside of which they can incinerate it in 20 minutes.
They appear to have a very factual, analytical and emotionless kind of intelligence.
They are known to use extradimensionnal prison in which they lock up galactic criminals.
Source: Doctor Who Universe, (DW: The Eleventh Hour)