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TAMU MARB 435 - Information on Echinoderms
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MARB 435 1st Edition Lecture 21Current LecturePhylum Echinodermata part 2Class Echinoidea About 950 species Grazers on hard substrates Body wall ossicles are fused to form an internal test pedicellariae between spines Have no arms Ambulacra extend toward the aboral pole  Aboral surface is restricted to small area around anusLocomotion Combination of spines and tube feet If turned upside down, they can right themselves Can move in any direction without turning around (no anterior or posterior end in regular urchins)Aristotles lantern Highly developed jaw apparatus Composed of ossicles and muscles• Used for grazing on hard substrates (sediment-dwelling species usually lack Aristotle’s lantern)Irregular UrchinsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Secondary bilateral symmetry Anus shifted towards the outer rim of the body Move along a fixed anterior-posterior axis Adapted to move over or through sand or mud Short spines used for locomotion instead of tube feet Mostly selective deposit feedersReproduction All echinoids are gonochoric 5 gonads (fewer in irregular urchins) are suspended in the ambulacra on the inside of the test Mostly free spawners: sperm and eggs are shed into the seawater Some cold water species brood their offspringDevelopment Typical deuterostome development Radial cleavage Hollow blastula Gastrulation by invagination Mesoderm forms from archenteron Coelom forms by enterocoelySea Urchin Grazing Positive effects: keeps algal growth in check on coral reefs Example: Diademaantillarum Negative effects: can turn kelp forests into urchin barrens Examples: Strongylocentratusspp., Lytechinussp., CentrostephanusrodgersiDiademaantillarum Was once the most abundant sea urchin in the Caribbean No commercial importance Inhabits sheltered areas, e.g. depressions in coral Moves to more open habitat at night Omnivorous, but mostly grazes on algae Keystone herbivore: maintains balance between algal growth and coralsMass Mortality 97% of the Caribbean population died in 1983-1984 of unknown causes Seemed to be affected by a waterborne pathogen Disease spread quickly and killed entire populations within daysConsequences Lack of grazing activity: reefs become overgrown with algae In Jamaica algal cover increased from 1 to 95% within two years of the urchin die-off Algae block off sunlight to coral symbionts Limit surface for coral larval recruitment Slow recoveryClass Holothuroidea About 1,200 species (about 1/3 deep sea) Many different habitats Burrowing in sand Epibenthic on sand Hard substrate Crevice dwellers On algae A few pelagic species Size range: a few mm to 2 mRespiratory Trees inhalation: contraction of cloacal dilator muscles  inrush of water  closing of anal sphincter  contraction of cloaca  water is pressed into respiratory trees  exhalation: contraction of the trees  water is forced out again Respiratory trees are absent in some small species which accomplish gas exchange over the body surfaceCuvieran Tubules• Tubules attached to the main branches of the respiratory trees in some species• Can be ejected through anus as a predator defense• Sticky and poisonous (saponins) • Can immobilize and eventually kill an attackerSea pigs Reproduction and Development Single, branched gonad (all other echinoderms have more than one) Mostly free spawners, but some brood their offspring on their body surfaceNutrition and Medicinal Value Low in fat 55% protein 10-16% mucopolysaccharides (important to form cartilage) Medicinal uses: chondroitin sulfate: relieves arthritis pain and is a virus inhibitor (patented in Japan for HIV therapy) saponins: anti-inflammatory and anti-cancer properties Sea cucumber oil: contains anti-inflammatory


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