MARB 435 1st Edition Lecture 21 Current Lecture Phylum Echinodermata part 2 Class 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 anus Locomotion 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 Urchins These 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 feeders Reproduction 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 offspring Development Typical deuterostome development Radial cleavage Hollow blastula Gastrulation by invagination Mesoderm forms from archenteron Coelom forms by enterocoely Sea 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 Centrostephanusrodgersi Diademaantillarum 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 corals Mass 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 days Consequences 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 recovery Class 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 m Respiratory 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 surface Cuvieran 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 attacker Sea 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 surface Nutrition 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 compounds