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Echinoderms
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Vocabulary Make the vocab list yourself as you learn about Echinoderms!
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Common Characteristics
Spiny skin Endoskeleton Radial Symmetry Water Vascular System
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Water Vascular System Network of seawater- filled tubes
Functions: movement, help obtain food, circulation One opening: madreporite Water pathway: Madreporite, stone canal, ring canal, radial canal, ampulla, tube foot Know this!
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Water Vascular System, Cont’d
How sea stars move: Pump water into tube feet These extend, attach to surface Then water flows out of tube feet They shorten, pulling sea star forward Ampulla - round, muscular sac Tube foot - suction cup, secretes mucus to stick to substrate 2 quick videos:
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Symmetry Radial Why is phylum so advanced, then? (Next slide, please)
Necklace sea star
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Symmetry Bilaterally symmetrical larvae grows into radially symmetrical adult 1st echinoderms bilatera Secondary radial symmetry
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5 Major Classes 1) Sea stars 2) Brittle stars
3) Sand dollars and sea urchins 4) Sea cucumbers 5) Sea lilies and feather stars (crinoids)
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(1) Sea Stars 5-20 arms surround central disk Knobby Sea Star
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Sunflower Sea Star
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(2) Brittle Stars Small with five long, thin arms; fragile
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More Brittle Stars
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(3) Sand Dollars Disc-shaped bodies Covered with tiny movable spines
Sediment feeders This shows only “test”, or endoskeleton
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and Sea Urchins Spherical bodies Sharp spines for defense
Grazers, sediment feeders or scavengers “Aristotle’s lantern” - 5 part mouth The Purple Sea Urchin is one of the sharp-spined urchin species. The spines are used as a means of defense against would-be predators. This urchin is deep purple in color, and grows to a diameter of about 4 inches. The are found along the western coast of the U.S. and Canada where they clink to depressions in the rocks during low tide.
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Aristotle’s Lantern You’re looking at the mouth on the oral side
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Stronglyocentrotus droebachiensis
Longest scientific name in the world!
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(4) Sea Cucumbers Think “sideways, elongated sea urchin”
5 rows of tube feet Sticky tentacle-like tube feet surrounding mouth; eats organic debris in sand Shoots thin tubules out anus when threatened - can eject entire digestive system!
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(5) Sea lilies and Feather Stars
Most ancient group - few species left Mouth on dorsal side Sea Lilies Sessile, have stalks Feather Stars Can creep or swim crinoid swimming!
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From here, we are talking about sea stars
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Some have no anus Very little released thru anus
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Digestive System Feed on clams, oysters, snails. . . Mouth is located on the ORAL side (underneath) Stomach in central disk, digestive glands in arms To eat: pry shell of prey open, evert stomach, digest prey in its shell, suck up soup Small prey eaten whole, shells ejected through mouth Note: “evert” means to turn inside out Some have no anus Very little released thru anus
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Respiration Diffusion across skin of tube feet
Some also have tiny skin gills for diffusion Some have no anus Very little released thru anus
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Excretion Diffusion across skin of tube feet and gills
Some have no anus Very little released thru anus
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Circulation O2, metabolic wastes carried by water vascular system, but no true circulatory system Some have no anus Very little released thru anus
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Nervous System No brain
Nerve ring circles mouth and connects with 5 radial nerves Extensive sensory nerve network coordinates movement of spines/feet Tip of arms have light-sensitive eyespot and nerves to sense food/chemicals One arm leads, others follow
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Reproductive System Most - dioecious
Two gonads in each arm, open directly to outside External fertilization Sea stars can regenerate arms 1st echinoderms bilatera Secondary radial symmetry
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