Phreatichthys andruzzii

Phreatichthys andruzzii is a species of ray-finned fish in the family Cyprinidae. It is the only species of the genus Phreatichthys, and is endemic to Somalia. This cave-adapted fish is whitish (non-pigmented) and blind. It is considered to have evolved in the cave environment for some two million years. Its name derives from the Greek words phreasatos for spring, and ichthys for fish. It grows to a maximum length of 6.2 centimetres (2.4 in).

This fish is the first animal discovered that does not adjust its biological clock with the light of the Sun. It has an unusual internal clock, which measures the passage of time with an extremely long period (up to 47 hours). It is also completely blind to all light stimuli.