Eck's species

Eck's species is a mysterious unnamed species of sapient bidimensional creatures native to a two-dimensional realm. As such, they physically have height and width, but no depth.

Biology
When crossing over into the tridimensional world, Eck's species appear as floating paper-thin aliens with a luminous contour and six limbs, and produce static noises. They're practically blind in their natural state, but wear removable artificial eyes in order to see. In their native realm, they're eyeless, and "see" with other senses, which don't work properly in three dimensions. Highly intelligent, they're also capable of speech.

Under normal circumstances, they are completely invisible, unless seen through lenses made from meteoric quartz. They also become visible when charged with electricity. They can pass through walls at will by going sideways, but are also able to cut through walls by tilting themselves in the right angle, or even going straight on, the latter which leaves a hole on the wall shaped like the creature's body.

Eck's species is extremely vulnerable to fire, which consumes them almost instantly. Electric shocks, on the other hand, only seem to make them visible and disoriented. They can't assimilate three-dimensional food.

Culture and society
The two-dimensional creatures are an advanced species and have knowledge of time warps and other dimensions.

Appearances

 * The Outer Limits, s02e03, "Behold, Eck!" (1964)