Created By: Sarah Butler
http://animals.nationalgeographic.com/animals/invertebrates/starfish/
Sea stars are purely marine animals, even using
[2] sea water instead of blood to pump nutrients throughout their bodies.
Marine scientists have undertaken the difficult task of replacing the beloved starfish’s common name with sea star because, well, the
starfish is not a fish. It’s an echinoderm, closely related to sea urchins and sand dollars.
There are some
2,000 species of sea star living in all the world’s oceans, from
[1] tropical habitats to the cold seafloor. The
five-arm varieties are the most common, hence their name, but species with
10, 20, and even 40 arms exist.
They have
bony, calcified skin, which
protects them from most predators, and many wear
striking colors that camouflage them or
scare off potential
attackers. Purely marine animals, there are no freshwater sea stars, and only a few live in brackish water.
Beyond their distinctive shape, sea stars are famous for their ability to
regenerate limbs, and in some cases, entire bodies. They accomplish this by housing
most or all of their vital organs in their arms. Some require the central body to be intact to regenerate, but a few species can
grow an entirely new sea star just from a portion of a severed limb.
Most sea stars also have the remarkable ability to
consume prey outside their bodies. Using tiny, suction-cupped tube feet, they
pry open clams or oysters, and their sack-like cardiac
stomach emerges from their mouth and oozes inside the shell. The stomach then
envelops the prey to digest it, and finally withdraws back into the body.
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