Sleep in animals

Common card · No. 259501

Sleep is broadly considered a biological necessity in virtually all animals. The large majority of such taxa with documented sleep physiology are bilaterians, though there is increasing evidence of sleep or sleep-like states in non-bilaterians such as Cassiopea jellyfish and hydra (both cnidarians), and sponges. The various criteria which biologists use to define sleep states have been observed in all other animal phyla, often with profound variation in function. In all of these taxa except sponges, regulation of sleep is documented to involve genes whose transcription oscillates with time, known as circadian or clock genes. These genes and the gene networks they regulate give rise to the internal circadian clock. The three categories of biological sleep schedules are diurnal, nocturnal, and crepuscular which characterize species whose waking periods mostly overlap with day, night, and twilight respectively. Specific sleep patterns and durations vary widely among and sometimes within sleeping...

Read on Wikipedia · Image Christian Ursilva from København, Danmark, CC BY-SA 4.0