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Fast Facts About Sea Animals

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Covering two-thirds of the earth's surface, the oceans and seas hold 99 percent of the earth's living space. Sea-life began over 3 billion years ago. Sea animals are found in various forms, with diversity in their diets, habitats and lifestyles. Microscopic plants are at the bottom of the marine animals' food chain, followed by microscopic animals. Third in the food chain are crustaceans, and then fish. Mammals are at the top of the food chain.


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Fish have gills that metabolize oxygen from the seawater. They are cold-blooded and lack digits. Some fish have both male and female sex organs, and some change sexes during their lifetimes. Oarfish are 50-foot long, snake-like creatures with a head that resembles a horse. Seahorses are fish that swim in an upright position. The female seahorse lays eggs in the male's brood pouch, where he keeps them until they hatch.


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Crustaceans are arthropods, and have a hard, flexible exoskeleton. Their bodies are made up of connected sections that create movable joints. Barnacles, crabs, crayfish, hermit crabs, krill, lobsters and shrimp are some of the animals that are crustaceans. Crustaceans use gills to breath. They have compound eyes that usually are on stalks, two pairs of antennae, a pair of mandibles and two pair of maxillae. Over 30,000 species of crustaceans live in the sea.

Marine Mammals

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Marine mammals are protected by the Marine Mammal Protection Act, in effect since 1972. They breathe air, give live birth to their babies and produce milk to feed their young. Marine mammals are carnivores. Dolphins, seals, sea lions, manatees and whales are sea mammals. There are only 300 to 400 North Atlantic right whales still in existence, making them the rarest marine mammal. The blue whale is the largest known animal in the world, and most can be found off the coast of California.

The American Horseshoe Crab

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American horseshoe crabs are unlike any other sea animal. They are not crabs, but are related to scorpions, spiders and ticks, existing for over 250 million years without changing form. The horseshoe crab's light blue blood is used in the medical field for tests that detect septic shock, causing toxins in medicines. They are returned to the water unharmed after donating their blood. Horseshoe crab eggs are the main sustenance for many migrating seabirds.