A pufferfish fills its stomach with water or air to ward off predators while some species have spikes that prevent animals from eating them. They're also highly poisonous and any animal that eats a pufferfish is in for a deadly surprise. The pufferfish's venom is dangerous for humans too and there is no known cure. In Japan these poisonous fish are served for dinner. Only a special chef trained to take out the poison is allowed to cook a puffer. Puffers eat algae and occasionally other animals like clams and mussels. They can be up to three feet long and over 100 species of pufferfish live throughout the world's oceans.
Jellyfish are beautiful but can be dangerous. As a species they are millions of years old and lived in the oceans before dinosaurs lived on land. They can be found along coastlines, deep water and water that is cold or warm. Jellyfish can be very tiny, the size of a fingernail, and others have tentacles over 100 feet long. The varying species can look very different from each other, but each jellyfish has tentacles that come out from its body and trail behind it as it swims. These tentacles have many stingers to paralyze and kill the jellyfish's prey. Certain jellyfish species are more dangerous than others and some are even poisonous to humans. One jellyfish in Portugal, called the man-of-war, has a bite as toxic as a cobra snake. Even a dead jellyfish can sting.
The Blue Whale is the largest animal living on the planet, growing to over 100 feet long. A baby blue whale gains 200 pounds per day in its first year of life. Whales can hold their breath for a long time under water, but they have to breathe air. They have a blow hole on top of their body they use like people use their noses, to take in oxygen. They are found in every ocean and spend their summers in cold, polar seas. These huge animals feed entirely on a tiny little animal called krill. Whales don't have teeth instead they have 400 plates that work as a sifter, letting in tons of the tiny animals per day. The average blue whale lives as long as a person, 80 to 90 years.
The hammerhead shark has a flat, mallet-like head that it uses to trap its favorite food, the stingray, to the ocean floor to kill it. The hammerhead's mouth is on the underside of its belly and its teeth look like the serrated edge of a knife. Hammerheads don't lay eggs; instead they have live babies, like humans. But a hammerhead can have many more babies at one time, up to 50. Hammerheads live for 20 to 30 years. There aren't many cases of them attacking humans since they aren't very aggressive. But they are very efficient when attacking prey, so people should keep their distance.