Dolphins always sleep with one eye open. This is because they don't breathe automatically and their brains need to remind them to surface and breathe, so only half of a dolphins brain sleeps at a time. So, the eye on the 'awake' side stays open.
Sleeping Dolphin
An octopus has a rectangular shaped pupil in its eye. This is a very sensitive eye that focuses like a camera lens. It can narrow to a slit, or go wide angle. It needs and eye that can refocus quickly so that it can see and control its long arms.
Rectangular octopus eye.
The giant squid is the largest invertebrate in the world and has the largest eyes of any animal. These can be forty centimetres across. A giant squid can reach a size of 60 feet in length but are difficult for marine biologists to study because they live at such great depths.
Giant Squid.
The starfish has no brain and is able to turn itself inside out. It is not a fish but closely related to the sea urchins.
Sea Star
A jelly fish doesn't have as brain, eyes, ears, heart, or bones. It's entire body is made up of 95% water.
Jelly Fish
A shrimp doesn't wear its heart on its sleeve as the saying goes. It keeps it in its head.
Shrimp
Oysters don't stay the same sex. They change each year.
Sydney Rock Oysters
The seahorse is the only species of animal where the male becomes pregnant.
Pregnant Seahorse (male.)
Giant electric eels can deliver more than 650 volts of electricity in one shock. They live in muddy water and have poor eyesight so they rely on electrical signals to move around. This ability to stun is their only defence.
Electric eel.
The blue whale makes the loudest sound made by any animal. Its whistle reaches 188 decibels. The sound can be heard for hundreds of miles. The sound of a jet plane taking off is 140 decibels and a human shouting reaches 70 decibels.
Blue Whale
