While most starfish are less than 6 inches wide, some of the world's largest species grow up to 3 or 4 feet. When measuring a starfish's width, marine biologists always includes its arms, which are known as rays. Each of the world's largest starfish has its own distribution range, so they rarely compete for food or territory.
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Midgardia xandaros are native to the Caribbean Sea and the Gulf of Mexico. This starfish does not have a large body, but each arm reaches out 2 feet. Most Midgardia xandaros starfish have an approximate diameter of 4 feet. These starfishes have up to 12 rays. In the Gulf of Mexico, Midgardia xanadros may live 2,000 feet below the water's surface. Midgardia xanadros belong to the Brisingid group of starfish and was discovered in 1970.
Although they are born with five arms, adult sunflower stars (Pycnopodia helianthoides) have up to 24 rays. Sunflower stars have a diameter of approximately 3 feet when they reach adulthood. These sea stars have some disconnected pieces in their skeletal structure; the disconnected pieces allow the sunflower star to expand its mouth to swallow large prey. Sunflower stars are large enough to prey on squid. These marine animals are native to North America's Pacific Coast.
Crown-of-Thorn Sea Star
Also known as Acanthaster planci, the crown-of-thorn sea star grows to between 1 and 2 feet. However, some specimens have grown up to 2.5 feet. This starfish receives its name from its spiny exterior; the crown-of-thorn's spines measure one-tenth of an inch. The crown-of-thorns spines are poisonous, which prevents predators from eating them. These starfishes have 13 to 16 rays when they are adults. Crown-of-thorn sea stars are native to the Indian and South Pacific Oceans.
The Evasterias echinosoma starfish lives in the Pacific Ocean on the eastern coast of Russia. This starfish grows between 2 and 2.5 feet. Evasterias echinosoma has five rays on its body. Physical characteristics of the starfish are rounded sides and short needles on its rays. These marine animals live at depths of 300 to 400 feet. Other echinoderms and mollusks are the primary diet items of Evasterias echinosoma.
Northern Pacific Seastar
Native to Australia's coastal region, the Northern Pacific seastar (Asterias amurensis) grows over 1 foot in width as an adult. This starfish is usually yellow or bright orange, but some species may be a dark violet. Northern Pacific seastars live at depths of 80 feet. Since they are not large enough to prey on cephalopods, Northern Pacific seastars usually search for sea snails, mollusks and crabs when they are hungry. This starfish has five rays.
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- Western Australia Department of Fisheries: Northern Pacific Seastar