The deep sea

Animals of the water column and sea floor below the reach of sunlight.

• Giant SquidArchiteuthis dux
• Giant Tube WormRiftia pachyptila
• Vampyroteuthis infernalis
• Grimpoteuthis discoveryi
• Pompeii WormAlvinella pompejana
• Giant IsopodBathynomus giganteus
• Sperm WhalePhyseter macrocephalus

About this list

Below about a thousand metres there is no sunlight, and most of what light exists is made by the animals themselves. Bioluminescence is the norm rather than the exception down here.

Two patterns recur. Gigantism: the giant isopod is a woodlouse relative the size of a cat. And chemosynthesis: the tube worms of hydrothermal vents have no gut at all, and live on sulphide-oxidising bacteria housed inside their own tissue — the first ecosystem found that does not ultimately run on sunlight.