Deep-Sea Animals: Strange Creatures of the Ocean Depths

The ocean’s depth zones

Scientists divide the open ocean into layers by depth and light:

The deepest known point, the Challenger Deep in the Mariana Trench, lies about 10,935 m (35,876 ft) down. There, the pressure is more than 1,000 times that at the surface.

How deep-sea animals survive

Darkness. Below 1,000 m (3,300 ft), the only light is made by animals themselves. Many deep-sea animals glow, as our list of bioluminescent animals explains, while others have huge eyes to catch faint flashes, or no working eyes at all. Red or black bodies are hard to see, because red light never reaches these depths.

Scarce food. Most food arrives as marine snow, a slow rain of dead plankton and waste from above. Predators often have big mouths, stretchy stomachs and slow metabolisms so that they can survive long gaps between meals. A dead whale on the seafloor can feed scavengers for years.

Pressure and cold. Deep-sea animals have few air spaces that pressure could crush, and their proteins work under conditions that would disable those of surface animals. Many fish build up a molecule called TMAO that keeps proteins stable, and the amount needed may explain why no fish has been found much below about 8,300 m (27,000 ft). In most of the deep sea the water stays at about 1–4 °C (34–39 °F) all year.

1. Anglerfish

Female deep-sea anglerfish carry a glowing lure on a modified fin spine and wait for prey to swim close to their wide, toothy mouths. The humpback anglerfish lives mainly at 200–1,500 m (660–4,900 ft), and females reach only about 15 cm (6 in). Males are tiny, under 3 cm (1.2 in); in some anglerfish families they fuse permanently to the female’s body. Read more in How do anglerfish mate?

2. Pelican eel

The pelican eel, or gulper eel (Eurypharynx pelecanoides), grows to about 75 cm (2.5 ft) and has a loosely hinged mouth much bigger than the rest of its body. Despite that huge gape, it seems to feed mostly on small crustaceans. The tip of its long, whip-like tail carries a light organ.

3. Fangtooth

The common fangtooth (Anoplogaster cornuta) is only about 18 cm (7 in) long, but its fangs are among the largest, relative to body size, of any fish. Adults live at about 500–5,000 m (1,600–16,400 ft), while the young stay nearer the surface.

4. Barreleye

The barreleye (Macropinna microstoma) has a transparent, fluid-filled dome on its head, through which its green, tube-shaped eyes can be seen. It hangs almost motionless at about 600–800 m (2,000–2,600 ft). Scientists studying it off California reported in 2008 that its eyes can rotate inside the dome to look up or forward.

5. Black swallower

The black swallower (Chiasmodon niger) is usually 15–20 cm (6–8 in) long, but its stretchy stomach lets it swallow fish more than twice its own length and up to 10 times its weight.

6. Viperfish

Sloane’s viperfish (Chauliodus sloani) has needle-like fangs so long that they do not fit inside its closed mouth; instead, they form a cage that traps prey. Light organs along its body help it hide and may help attract prey.

7. Tripod fish

The tripod fish (Bathypterois grallator) stands on the seafloor on three long, stiff fin rays, two pelvic fins and its tail, facing into the current. Raised above the mud, it waits for small crustaceans to drift into reach.

8. Frilled shark

The frilled shark (Chlamydoselachus anguineus) is an eel-like shark up to about 2 m (6.6 ft) long, with around 300 small, three-pointed teeth. Its pregnancy may last up to 3.5 years, possibly the longest of any vertebrate.

9. Goblin shark

The pink goblin shark (Mitsukurina owstoni) has a long, flat snout full of electrical sensors and jaws that shoot forward to snatch prey. It lives on continental slopes and has been filmed as deep as about 2,000 m (6,600 ft).

10. Mariana snailfish

The Mariana snailfish (Pseudoliparis swirei) lives at about 6,200–8,000 m (20,300–26,500 ft) in the Mariana Trench, deeper than almost any other fish. It is pale and soft, up to about 29 cm (11 in) long, and has no swim bladder to be crushed. Other snailfish have been filmed below 8,300 m (27,200 ft), the deepest fish ever recorded.

11. Giant squid

The giant squid (Architeuthis dux) has eyes up to at least 27 cm (11 in) across, among the largest in the animal kingdom. Including its two long feeding tentacles, it can reach about 12 m (40 ft). Living giant squid were first filmed in their natural deep-water habitat in 2012, off Japan.

12. Colossal squid

The colossal squid (Mesonychoteuthis hamiltoni) of the Southern Ocean is shorter than the giant squid but much heavier. A specimen caught in 2007 weighed 495 kg (1,091 lb), making it the heaviest invertebrate known. Its arms and tentacles carry swiveling hooks as well as suckers. Compare the two in giant squid vs colossal squid.

13. Vampire squid

The vampire squid (Vampyroteuthis infernalis) is neither a true squid nor an octopus. It lives in low-oxygen water where few predators can follow, feeds on marine snow and, when threatened, releases a cloud of glowing mucus.

14. Dumbo octopus

Dumbo octopuses (genus Grimpoteuthis) flap ear-like fins to swim slowly above the seafloor. They are the deepest-living octopuses known: a sighting at 6,957 m (22,825 ft) in the Java Trench of the Indian Ocean was reported in 2020.

15. Giant isopod

The giant isopod (Bathynomus giganteus) is a relative of woodlice that usually grows to 19–36 cm (7.5–14 in), with confirmed specimens up to about 50 cm (20 in). It scavenges dead animals on the seafloor and copes with long famines; captive isopods have survived more than five years without food.

16. Yeti crab

The yeti crab (Kiwa hirsuta), discovered in 2005 near hydrothermal vents in the South Pacific, is about 15 cm (6 in) long and has legs covered in pale, silky bristles. Bacteria grow on these bristles, and related yeti crabs appear to feed on them.

17. Supergiant amphipod

Amphipods are small shrimp-like crustaceans that swarm over any food that reaches the seafloor. Most are tiny, but the supergiant amphipod (Alicella gigantea) reaches 34 cm (13 in). Other amphipods scavenge in the deepest trenches, including the Challenger Deep.

18. Giant tube worm

Giant tube worms (Riftia pachyptila) live around hydrothermal vents on the Pacific seafloor and can reach 3 m (10 ft) long. They have no mouth or gut. Instead, bacteria inside their bodies turn chemicals from the vents into food, a process called chemosynthesis. Scientists first found them in 1977 on the Galápagos Rift.

19. Sea pig

Sea pigs (genus Scotoplanes) are sea cucumbers that walk across abyssal plains on enlarged tube feet, usually at 1,200–5,000 m (3,900–16,400 ft). They gather food from the mud, eating dead organic matter that has settled on the bottom.

20. Venus’ flower basket

The Venus’ flower basket (Euplectella aspergillum) is a glass sponge whose skeleton is a delicate lattice of silica. A pair of small shrimp often enters the sponge when young and grows too large to leave, spending the rest of its life inside.

Visitors from the surface: diving whales

Some air-breathing mammals visit the deep sea to hunt. Sperm whales dive well beyond 1,000 m (3,300 ft) to catch squid, and Cuvier’s beaked whale holds the mammal records, with dives to 2,992 m (9,816 ft) and up to 222 minutes long. See How deep can whales dive? for more.