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Echinoderms and Invertebrate Chordates
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Echinoderms Members of the phylum Echinodermata
Sea Stars, Sea Urchins, Sea Cucumbers and Sea Lilies
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Pineapple Sea Star
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Brittle Star
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Crown of Thorns
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Sea Urchin
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Feather Star
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Feather Stars
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Echinoderm Characteristics
All Echinoderms have a hard, spiny or bumpy endoskeleton composed of calcium carbonate which is covered by a thin epidermis
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Rays Long, tapering arms of a sea star which are covered with short rounded spines
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Pedicellariae Spines of some sea stars and sea urchins have become modified into pincer like appendages Used for protection and for cleaning the surface of its body
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Radial Symmetry Is an advantage to animals that are stationary or move slowly Enables animals to sense potential food, predators and other aspects of their environments Is a circular body plan
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Basket Star
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Sea Lily
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Water Vascular System Enables Echinoderms to move, exchange gases, capture food and excrete wastes Is a hydraulic system that operates under water pressure
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Madreporite A sieve like, disk shaped opening on the upper surface of the echinoderm’s body Water enters and leaves the water vascular system through this opening
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Tube Feet Hollow, thin walled tubes that end in a suction cup
Look somewhat like miniature droppers Each tube foot works independently of the others
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Ampulla Round muscular structure which works something like the bulb of a dropper located at the base of the tube feet
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Nutrition Sea stars are carnivorous and prey on worms or on mollusks such as clams Most sea urchins are herbivores and graze on algae Brittle stars, sea lilies and sea cucumbers feed on dead and decaying matter that drifts down to the ocean floor
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Sea Star Digestion To eat, a sea star pushes it stomach out of its mouth, releases powerful enzymes which turn solid food into a soupy liquid that the stomach can easily absorb
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Nervous System Echinoderms have no head or brain, but they do have a central nerve ring that surrounds the mouth Nerves extend from the nerve ring down each ray Each radial nerve then branches into a nerve net that provides sensory information to the animal
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Senses Echinoderms have cells that detect light and touch, but most do not have sensory organs Sea stars are an exception-at the tip of each ray on the underside is an eye spot which consists of a cluster of light detecting cells
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Larvae Have bilateral symmetry, a feature more common to chordates
Ciliated larvae develop from the fertilized egg of en echinoderm then becomes a mature adult through dramatic changes known as metamorphosis
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Diversity of Echinoderms
Approximately 6000 species exist today Four classes Ophiuroidea-brittle stars Echinoidea-sea urchins and sand dollars Holothuroidea-sea cucumbers Crinoidea-sea lilies and feather stars
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Sea Stars Most species have five rays, but some have up to 40
Rays are tapered and extend from the central disk
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Brittle Stars Extremely fragile, parts of its rays will break off, an adaptation that helps it survive when attacked by a predator Do not use tube feet for locomotion, propel themselves with a snakelike, slithering motion Tube feet pass particles of food to the mouth
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Sea Urchins Globe or disk shaped animals covered with spines
Do not have rays Look like living pin cushions, spines protect them from predators
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Sand Dollars Sand dollars have a flat, circular skeleton with a five petaled flower pattern on the surface A living sand dollar is covered with small, hair like appendages Tube feet on the top are modified into gills, those on bottom aid in bringing food particles to the mouth
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Sea Cucumbers Vegetable like appearance
Have a leathery covering which allows them to be more flexible than other echinoderms Use tentacles and tube feet to pull themselves along the ocean floor May expel a tangles mass of sticky tubes or rupture releasing some internal organs when threatened
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Sea Cucumber
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Sea Lilies Are sessile-cannot move around
Body is on a stalk attached to the ocean floor Are filter feeders
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Feather Stars Larvae are sessile
Adult feather star uses its feathery arms to swim from place to place
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Chordates Includes 3 subphyla
Urochordata-sea squirts Cephalochordata-lancelets Vertebrata-the vertebrates Have a notochord-a dorsal hollow nerve cord
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Invertebrate Chordates
Have no backbone, gill slits, and muscle blocks Bilateral symmetry All chordate embryos have a notochord
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Notochord A long semirigid, rodlike structure located between the digestive system and the dorsal hollow nerve cord Made up of large, fluid-filled cells held within stiff fibrous tissues in invertebrate chordates
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Notochord
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Dorsal Hollow Nerve Cord
Develops from a plate of ectoderm that rolls into a hollow tube Composed of cells surrounding a fluid-filled canal that lies above the notochord Cells in the posterior portion become the spinal cord, the anterior portion develops into a brain
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Gill Slits Paired openings located in the pharynx, behind the mouth
Many chordates have several pairs of gill slits Used by some to strain food from the water and for gas exchange during respiration
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Muscle Blocks Modified body segments that consist of stacked muscle layers Are anchored by the notochord which gives the muscles a firm structure to pull against Aid in movement of the tail
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Tunicates Members of the subphyllum Urochordata
Have many of the shared characteristics of chordates during their larval stage
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Tunicates Also known as sea squirts
Larvae do not feed and are free swimming for only a few days after hatching The then settle and attach themselves with a sucker to boats, rocks and the ocean floor
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Incurrent siphon ▼ Pharynx-lined With gill slits ► ◄ Ciliated groove Excurrent siphon► ◄Heart ◄Stomach ◄Tunic
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Lancelets Cephalochordata
Small streamlined and common marine animals about 5 cm long Bury themselves in the sand with only their heads sticking out Filter feeders
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