The world's seas are filled with a variety of radically different life forms. While some of these are widely recognised thanks to their appearances in aquariums, many creatures lurk in the depths of Earth's deepest seas which appear almost alien in comparison.
A form of marine arthropod, crustaceans have a segmented exoskeleton and possess various appendages, including antennae and mandibles for feeding. Hermit crabs are best known for their unusual method of gaining a shell. Instead of growing a shell themselves, these crabs search for a discarded mollusc shell to use; once inside, they're very difficult to uproot. Found in crevices and holes in the sea, lobsters possess large claws for breaking down and grabbing food, as well as a tail which allows them to swim by flapping it. Lobsters are usually found walking along the seabed, however.
Mollusks are a huge animal group, with more than 80,000 species in existence. Mollusks don't all look alike, but tend to be similar internally. The blue ring octopus, for example, is distinctive thanks to its eight arms, which it can regenerate if needed, and the potency of its poison, which it uses to protect itself from predators such as moray eels. A cuttlefish, meanwhile, shares the eight arms of the octopus but also possesses fins for swimming, as well as the ability to propel itself through the sea by shooting water from its mouth. The cuttlefish also spits ink to disorient predators.
A hugely varied animal group, fish are split into several classifications, among them bony fish, so called because of the material found in their skeletons, and cartilaginous fish, which possess skeletons constructed of cartilage. A denizen of areas such as the Red Sea, the brightly coloured clown fish makes its home among the tentacles of sea anemones, which double as both a living space and a mode of protection against predators. The clown fish also eats the scraps of food left by the anemone, and also uses its bright patterns to attract other fish for the anemone to kill. Sharks make up 7 per cent of all fish, with numerous varieties in existence. All sharks are cartilaginous fish, giving them usefully lightweight skeletons. Their large livers also help to give these heavy fish buoyancy.
Echinoderms are symmetrical creatures recognisable by the various arms which protrude from all over their bodies. They lack brains and eyes, and use tentacles tipped with suction pads to slowly move around. Feather stars are a species of echinoderm with many arms, with some varieties having up to 200. These arms appear feathery, hence the creature's name. They employ a sticky material to aid in capturing food. Sea urchins are distinctive thanks to the potentially poisonous spines covering their bodies. They possess sharp teeth, as well as tiny pincers which they use to catch prey.