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sea star
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sunflower starfish high Arctic sea star
Study how sieve plates and suction-cupped tube feet enable sea stars to catch prey and move through water
watch a starfish's tube feet pry open a mussel's shell and extrude its stomach onto the mussel
Observe sea star reproduction, from egg and sperm release and fertilization to development of zooplankton embryos and larvae
Crown of thorns starfish (Acanthaster planci). firebrick starfish A bright red starfish with five arms rests on wet rock and green sea grass.
examine a variety of echinoderm species such as starfish, basket star, sand dollar, and sea cucumber
Principal features of a starfish. Water for the water vascular system enters through the madreporite and passes into a ring canal and on to radial and lateral canals, from which it enters the tube feet, which are connected to saclike ampullae on top. Contraction of the tube feet forces water into the ampullae, creating suction that allows suckers at the ends of the feet to hold to a surface. When the ampullae contract, water is forced into the feet, extending them and releasing the suction. These coordinated actions permit movement, attachment, and capture of prey. In many starfish, the cardiac stomach is everted through the mouth on the body's undersurface to envelop prey, and digestion may begin outside the body before the stomach is drawn back in.
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sunflower starfish
sunflower starfish Sunflower starfish (Pycnopodia helianthoides).

sea star

echinoderm
Also known as: Asteroidea, starfish
Written and fact-checked by
Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
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sea star, any marine invertebrate of the class Asteroidea (phylum Echinodermata) having rays, or arms, surrounding an indistinct central disk. Despite their older common name, they are not fishes. The roughly 1,600 living species of sea stars occur in all oceans; the northern Pacific has the greatest variety. Most species are 20 to 30 cm (8 to 12 inches) across; some are only 1 cm (0.4 inch), and others are as much as 65 cm...

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