75% of sea creatures glow in the dark

Sunlight from the surface doesn't penetrate farther than 650 feet down. Beyond that, it's a lightless expanse for the remaining 13,350 feet down to the ocean floor.

Most of us have seen footage of flickering, glowing deep sea creatures. But a new study shows that fully 75% of the ocean's creatures bioluminesce, which means that the depths of the ocean may not be nearly as dark as we might have thought. And in some categories, like jellyfish and jellyfish-like creatures (siphonophores), up to 99% of the species is able to glow.

Many of these creatures give off only a faint glow. So faint, in fact, that until recently, cameras were not able to capture it. However, the glow is bright enough for the creatures' purposes - and for those of their predators, as well.

Earlier studies were no doubt also thrown off by the fact that many of these creatures can and do turn their bioluminescence on and off at will. Light attracts food, but it also attracts predators.

And it's expensive to produce, to boot. A deep sea creature needs to preserve its energy, given how difficult it must be to make a living in the depths.

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By NOAA/NMFS/SEFSC Pascagoula Laboratory

Striped anglerfish ( Antennarius striatus ). Gulf of Mexico.

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First footage of deep-sea anglerfish pair

Vampire squid

The vampire squid (Vampyroteuthis infernalis, lit. "vampire squid from Hell") is a small cephalopod found throughout temperate and tropical oceans in extreme deep sea conditions.

The vampire squid uses its bioluminescent organs and its unique oxygen metabolism to thrive in the parts of the ocean with the lowest concentrations of oxygen.

This organism has two long retractile filaments, which distinguish it from both octopuses and squids, and places it in its own order, Vampyromorphida. As a phylogenetic relict, it is the only known surviving member of its order

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By Citron

Adult vampire squid (Vampyroteuthis infernalis)

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The vampire squid can turn itself "inside out" to avoid predators.

Crystal Jellyfish

Aequorea victoria, also sometimes called the crystal jelly, is a bioluminescent hydrozoan jellyfish, or hydromedusa, that is found off the west coast of North America.

The species is best known as the source of two proteins involved in bioluminescence, aequorin, a photoprotein, and green fluorescent protein (GFP).

Almost entirely transparent and colorless, and sometimes difficult to resolve, Aequorea victoria possess a highly contractile mouth and manubrium at the center of up to 100 radial canals that extend to the bell margin.

The bell margin is surrounded by uneven tentacles, up to 150 of them in fully-grown specimens. The tentacles possess nematocysts that aid in prey capture, although they have no effect on humans.

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By Sierra Blakely

Ventral view with hyperiid amphipod

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By Sierra Blakely

Ventral view with hyperiid amphipod

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Crystal jellies are very transparent about their life in the open ocean.

The frilly mouth of the jelly—it's the little clapper below the bell—can extend to nearly the size of the jelly itself to swallow food.

In this video, you can see the mouth in action, moving along the bell edges to slurp food from the tentacles. Radial canals—the "spokes on a wheel"— then move nutrients about the jelly.