Sea Stars

雪儿 · 发表于: 2011-7-8 12:21:04

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Sunflower Sea Star

Photograph by Paul Nicklen, National Geographic

A sunflower sea star is draped moplike over a seafloor rock off the British Columbia coast. Though commonly called starfish, sea stars are not fish but echinoderms, more closely related to sea urchins and sand dollars. Only the five-armed species really resemble stars—others may boast as many as 40 appendages.

雪儿 · 发表于: 2011-7-8 12:21:18

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Sea Star’s Back

Photograph by Tim Laman, National Geographic

A close-up reveals the backside of a sea star in Indonesian waters. This star boasts a full complement of five arms but it may not always keep them. When grabbed by a predator, the sea star can simply lose a limb and later grow a replacement. In fact, some species can grow a new body from just a single severed limb and a small part of their central disk.

雪儿 · 发表于: 2011-7-8 12:21:32

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Basket Star

Photograph by Emory Kristof, National Geographic

Basket stars, like this one in California’s Monterey Bay, live along North America’s Pacific coast from the Bering Sea to California. The sea stars feed by using their intricate webs of branching arms to snag zooplankton drifting by in the current.

雪儿 · 发表于: 2011-7-8 12:21:47

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Sea Star on Mussel Bed

Photograph by George Grall, National Geographic

A colorful sea star heads toward a bed of mussels in Clallam Bay, Washington. Though they appear sedentary, sea stars move around on tiny, tubular feet. They also use their feet to pry open shellfish like clams and oysters, beginning a fascinating feeding style. The sea star injects its stomach into a clam’s shell, where it surrounds and envelopes its prey and digests it before retreating back into the sea star’s body.

雪儿 · 发表于: 2011-7-8 12:22:06

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Crown-of-Thorns Sea Stars

Photograph by Brian J. Skerry, National Geographic

Crown-of-thorns sea stars—like this group on Kingman Reef in the Pacific—can inflict a painful sting to humans, but they are far more dangerous to corals. Outbreaks of this fast-spreading sea star can cause high mortality on reefs where they feed. Scientists aren’t sure exactly what causes such outbreaks, or what their ultimate impacts may be on coral reef health.

雪儿 · 发表于: 2011-7-8 12:22:20

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Starfish

Photograph by Tim Laman, National Geographic

Some 2,000 sea star species live throughout the world’s oceans. Some weigh as much as 11 pounds (5 kilograms) and stretch more than 2 feet (65 centimeters) across, but others are only half an inch (1 centimeter) in diameter. These animals reproduce prolifically, and some sea stars can release millions of eggs into the water for fertilization at the same time.

雪儿 · 发表于: 2011-7-8 12:22:35

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Biscuit Sea Star

Photograph by Jason Edwards, National Geographic

Like sand dollars and sea urchins, sea stars are echinoderms, those of the “spiny skin.” Sea star skin is calcified to make the relatively sedentary animal a less appealing meal. It can also adopt a variety of hues to provide an effective camouflage.

雪儿 · 发表于: 2011-7-8 12:23:00

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Sun Star Feeding on Penguin Carcass

Photograph by Paul Nicklen, National Geographic

A sun star feeds on a penguin carcass in frigid Antarctic waters. Sea stars are opportunistic feeders. While some simply gather organic particles that float their way, others actively prey on clams or coral. This sun star is scavenging, making a meal of the remnants of a penguin left behind by leopard seals.

雪儿 · 发表于: 2011-7-8 12:23:10

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Arching Sea Star

Photograph by David Doubilet, National Geographic

Sea stars are remarkable for what they lack. They have no blood, but instead use filtered seawater to circulate nutrients throughout their bodies. They also lack brains, and their nervous systems stretch throughout theirs arms. Sea stars don’t have conventional eyes but “see” with light-sensitive eyespots located at the tip of each arm.

雪儿 · 发表于: 2011-7-8 12:23:22

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Sea Star

Photograph by Tim Laman, National Geographic

A sea star sits on the bottom of a shallow cove in Belize. These bottom-dwellers may be humble creatures, but they play important roles in the ocean ecosystem, including keeping populations of shellfish in check, and, according to recent studies, absorbing large amounts of carbon in the world’s oceans.

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