Only a few organisms are adapted to living in this band of oxygen-poor water. The vampire squid is one; the only cephalopod to tolerate the OMZ.
The vampire squid is something of a hybrid of squid and octopus; a living relic; the only modern representative of cephalopods before they split into 2 groups: one with 8 limbs, the other 10.
A vampire squid has 8 arms that are webbed together. It propels itself through the water by flapping 2 small fins, 1 on each side of the mantle.
Inside webbed limbs are 2 tactile filaments, which can extend well past their arms. These filaments let vampire squid forage.
Vampire squid are saprovores: feeding on marine snow and other detrital matter that comes around.
This relic is admirably adapted. Vampire squid can breathe normally when oxygen is just 3%. Their metabolic rate is the lowest of all deep-sea cephalopods. Their gills cover an especially large surface area. Their blue blood’s hemocyanin binds and transports oxygen most efficiently.
To help minimize physical requirements, the gelatinous tissues of vampire squid closely match the density of the surrounding seawater. Vampire squid have weak musculature but are able to stay agile and maintain buoyancy with minimal effort, thanks to balancing organs (statocysts) which are similar to the human inner ear.
Life in the slow lane has its advantages. Whereas all other soft-bodied creatures like it (coleoids) have a single reproductive cycle, vampire squid have multiple reproductive cycles.
Vampire squid are covered in photophores: tiny light-producing organs. They can exercise exquisite control over this multitude of luminescent spots: able to produce disorienting flashes of light for up to several minutes.
If threatened, the vampire squid releases a dazzling luminescent mucus from its arm tips that lets it disappear into the blackness without having to swim far.
This self-limited lifestyle has a large payoff. The only predators that vampire squid have are those transiently passing through the OMZ.