Anglerfish
In some deep-sea anglerfish, tiny males fuse permanently to much larger females, sharing their blood supply for the rest of their lives.
Oceans
Atlantic Bluefin Tuna
Bluefin tuna are warm-blooded fish: a heat exchange system in their blood vessels keeps their muscles much warmer than the surrounding water.
Atlantic Goliath Grouper
Goliath groupers can make loud, booming sounds with their swim bladders that divers can feel as well as hear.
Basking Shark
The basking shark is the second-largest fish in the world, and it filters up to about 2,000 tonnes of water an hour through its huge open mouth.
Bottlenose Dolphin
Each bottlenose dolphin develops its own signature whistle, which works like a name, and dolphins respond when they hear their own.
Bull Shark
Bull sharks can live in fresh water and have been found thousands of kilometres up the Amazon River and far up the Mississippi.
Clownfish
All clownfish are born male; when the dominant female of a group dies, the largest male changes sex and becomes the new female.
Common Octopus
About two-thirds of an octopus’s neurons are in its arms, which can taste, touch and act partly on their own.
Fin Whale
The fin whale is the second-largest animal on Earth, and so fast that sailors called it the ‘greyhound of the sea’.
Flying Fish
A flying fish can glide for about 50 metres or more, and one was filmed staying airborne for about 45 seconds by touching the water with its tail to keep going.
Giant Manta Ray
Manta rays have one of the largest brains relative to body size of any fish, and they appear to recognise themselves in mirrors in experiments.
Giant Oarfish
The giant oarfish is the longest bony fish in the world and is thought to be behind many legends of sea serpents.
Giant Squid
The giant squid has eyes up to about 27 cm across, the size of a football, among the largest eyes of any animal.
Great Barracuda
Great barracudas often follow snorkellers out of curiosity, watching them with their fang-filled jaws slightly open.
Great Hammerhead Shark
A hammerhead’s wide head, called a cephalofoil, spreads out its electrical sensors, helping it find stingrays buried in sand.
Great White Shark
Great white sharks can detect tiny electrical fields from living animals using sensory pores on their snouts called ampullae of Lorenzini.
Green Sea Turtle
Female green turtles return to the same beach where they hatched, sometimes after travelling thousands of kilometres, navigating partly by Earth’s magnetic field.
Greenland Shark
The Greenland shark is the longest-lived vertebrate known: scientists estimated one individual to be around 400 years old.
Hawksbill Sea Turtle
Hawksbills eat sponges full of glass-like spikes that would harm most animals, and by doing so they help keep coral reefs healthy.
Humpback Whale
Male humpbacks sing complex songs that can last up to 20 minutes, and whole populations change their song over time as new versions spread.
Leatherback Sea Turtle
The leatherback is the largest turtle on Earth and can dive deeper than 1,200 metres, deeper than any other reptile.
Lion’s Mane Jellyfish
The largest lion’s mane jellyfish ever recorded had a bell over 2 metres wide and tentacles about 37 metres long, longer than a blue whale.