BESSAN

A winged species that was conquered and destroyed by the Krillitane.
Source: Doctor Who, "School Reunion"

SEX MONSTER / SEX GAS

A gaseous alien parasite that feeds on orgasmic energy. Composed of vorax and ceranium gases, Earth's atmosphere is poisonous to the alien, so it needs to take a human host to survive for prolonged periods. It vies for control with its host, causing physiological changes that eventually cause the host's internal organs to explode.

The alien also makes its host secrete a blend of ultra-powerful pheromones that cause tremendous sexual attraction in those around it for the purposes of feeding. Coupling with the host is fatal, causing the host's partner to disintegrate into a pile of dust at climax and allowing the alien to absorb the energy from the orgasm.

A specimen came to Earth in a meteorite in the early 21st century and landed near Cardif. Although the technological level of the entitiy is unknown, it refered to the meteorite as his ship and said it came to Earth by design, so it has some knowledge of interstellar scale and has the ability to manoeuver through space in a container of some sort.

Source: Torchwood "Day One"

DOGONS

The Dogons are a space faring reptilian species with thirteen eyes, each of which grant them especially enhanced perceptions in various respects. A Dogon ship crashed near the british town of Cardif in the early 21st century and some dead specimen were dissected by human scientists.
Source: Torchwood "Random Shoes"

EXXILONS

Planet of Origin: Exxilon

A highly advanced civilisation of bald silicon-based humanoids with bulbous eyes and bark-like glowing skin, the Exxilon visited Earth and were mistaken for space gods in ancient Peru. They created the City, a huge complex imbued with artificial intelligence that turned on them, either killing them or casting them out. The surviving Exxilons then either reverted to stone-age savagery, worshipping the city and offering sacrifices to it; or fled the city and the savages but were persecuted by their peers and driven to the planet's lower levels. The mineral parrinium, the only antidote to the disease known as the space plague, was found only on Exxilon.

Source: Doctor Who "Death to the Daleks"

ARGOLINS

Planet of Origin: Argolis

Argolins are yellow skinned humanoid nhabitants of Argolis who developed an nascent interstellar civilisation until 2250, when after a 20-minute nuclear war with the Foamasi, their planet was tunred into a nuclear wasteland and the few surviving Argolins became sterile. The radiation also slowed down their metabolic rate, making them appear ageless for a long period of time, until they suddenly withered away in a matter of hours. The surviving Argolins rebuilt their civilisation around services to other civilisations and became leisure providers. They attempted to renew their race through cloning but with poor results until, in 2290, when they were on the verge of bankrupty, alien input allowed them to perfect a Tachyon Recreation Generator to rejuvenate their race.
Source: Doctor Who “The Leisure Hive”

ARCTURUS

Planet or origin: It is not known if the name of the species related to the star known to humans as Arcturus.
The arcturus are non humanoid multi-strand organisms with a roughly skull shaped mass with two eyes at its center. They cannot survive in Earth-like environments, unless immersed in a container filled with their native life fluids. They often have such containers equipped with traction unit to move around on alien worlds. They have developed an advanced space faring civilisation and, in the future, will be members of the same Federation as Earth and Alpha Centauri.
Source: Doctor Who, 'The Curse of Peladon", "The Beast of Peladon"