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2 Echinoderm Classes Asteroidea – Sea Stars : Multiple arms radiating from central disk Tube feet on bottom Ophiuroidea – Brittle Stars: Distinct central disk with snake like arms Tube feet lack suckers Riley Galton

3 Echinoderm Classes Echinoidea – Sea Urchins and Sand Dollars: No arms, but 5 rows of tube feet Have muscles that can move spines graphyiles/ Crinoidea – Feather Stars and Sea Lilies Flexible arms used in suspension feeding Haven’t changed in 500 million years http://lh6.ggpht.com Riley Galton

4 Echinoderm Classes Holothuroidea – Sea Cucumbers Reduced endoskeleton Five rows of tube feet Concentricycloidea – Sea Daisies Only two known species Disk shaped, less than 1cm in diameter Riley Galton

5 Echinoderm Sensory Structures Eyespots on the ends of ambulacra are sensitive to light Pedicellariae (jaw like skeletal structures used to keep organisms from settling on skin), tube feet, and spines are sensitive to touch Riley Galton

6 Echinoderm Reproduction Sexual: Eggs and sperm are released into the water where they are fertilized Larvae are planktonic Internal fertilization has been observed in certain species of sea stars, brittle stars, and sea cucumbers Asexual: Echinoderms can regenerate body parts and organs Asexual reproduction can occur (though not by will) if the echinoderm is torn with enough of the body on each part Riley Galton erfig.gif

7 Body Cavity (Coelom) PRESENT! Coelom = A fluid-filled cavity between body wall and gut; lined by mesoderm Two parts: Perivisceral coelom – large, fluid-filled cavity where major organs, digestive tube and sex organs, are suspended Water Vascular System - network of hydraulic canals unique to echinoderms that branches into extensions (tube feet) which function in locomotion, feeding and gas exchange Julia Heunis

8 Body Symmetry evolved from animals with bilateral symmetry adult echinoderms possess radial symmetry All echinoderms exhibit fivefold radial symmetry in portions of their body at some stage of life (5 parts around central axis), even if they have secondary bilateral symmetry For the most part… LARVAE ~ bilateral ADULTS ~ radial Julia Heunis wiki/Echinoderm

9 Excretory System NO true excretory system! Main opening of a sponge used only to EXPEL WASTE Anus leads directly from stomach/digestive tract Anus = top mouth = bottom Julia Heunis

10 Olivia Heunis

11 Skeletal Type Echinodermata: “Spiny Skinned” DO NOT possess an exoskeleton a thin outermost skin covers a mesodermal endoskeleton made of tiny calcified plates and spines - forms rigid support contained within tissues of the organism Skeleton composed of skeletal plates called ossicles Ossicles = small bones In some species, such as the sea urchin, plates of the skeleton are locked together to form a rigid structure. most sea stars and brittle stars can flex their ‘arms’ = skeleton has gaps, flexible plate junctures Julia Heunis

12 Other Unique Features Echinoderms can REGENERATE ex: sea cucumbers can eject a portion of gut in response to predators and regenerate when safe Water vascular system (described earlier) is unique to echinoderms; varies water pressure to control tube feet Crinoids and some brittle stars = passive filter-feeders, absorbing suspended particles from passing water sea urchins = grazers sea cucumbers = deposit feeders starfish = active hunters Julia Heunis

13 More Unique Features Autonomy = The spontaneous self amputation of an appendage when the organism is injured or under attack. The autotomized part is usually regenerated. “arms” → multiples of 5; some have more because of regeneration mutable collagenous tissue ~ connect ossicles; can maintain different positions without much effort Julia Heunis

14 Nervous System Decentralized central nerve ring surrounds gut, connect radial nerves. Radial nerves run under each arm, coordinate movement, etc. Do not have “brains,” but some have ganglia along radial nerves David Lin

15 Digestive System Complete digestive system (tubular gut), mouth to anus. (bottom to top) Crinoidia: filter-feed, use cilia Asteroidea: Cardiac (evert), pyloric stomach, digestive glands Urchins: “Aristotle’s lantern” (masticatory apparatus) Holothurians: suspension/deposit feeders, use tentacles. _Internal_Anatomy/id/2099728 David Lin k/pages/echinoderm.html

16 Locomotion/Musculature Utilize water vascular system and tube feet Water in from madreporite, pumped into ampulla by radial canal Ampulla contracts, water to podia Podia contracts, water to ampulla – Podia bend, shorten allows movement (vacuum and suction) David Lin m.jpg

17 Gas Exchange Asteroids, crinoids: dermal gills (thin epidermis) Urchins: infolds of body wall (bursae) opening to outside Sand dollars: modified podia on top (petaloids) which are thin-walled and flaplike. Holothurians: highly branched hindgut called "respiratory tree" David Lin rmata.html

18 Circulatory System Mostly in perivisceral coelom, enhanced by water vascular system and hemal system. – Hemal system: series of canals and spaces mostly in coelomic channels. Fluid movement by cilia. Used to distribute nutrients. No respiratory system. David Lin echinodermata.html echinodermata.html

19 Quiz 1. Echinodermata have ________ symmetry as larvae, but display ________ symmetry as adults. 2. What allows Echinoderms to function in locomotion, feeding and gas exchange? 3. Sea stars can grow new arms and sea cucumbers can replace their gut after ejecting them. What feature of echinoderms does this demonstrate? 4. Name the stomachs of a sea star. Functions?

20 Answers Bilateral, radial Water vascular system Regeneration Cardiac, pyloric; evert and enzymes, further digestion

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