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Unformatted text preview: Like protostomes, deuterstomes are triploblastic and eucoelomate. But they differ in the pattern of development: the anus ; mouth forms secondarily the mouth ; anus forms secondarily Blastopore forms: From gut, by enterocoely (archenteron outpocket pinches off to form coelom) Schizocoely (blocks of mesoderm split internally to form coelom) Origin of coelom Endodermal , from archenteron outpocket Ectodermal , from cells near blastopore Mesoderm formation Radial, indeterminate (cell fates established late in development) Spiral, determinate (cell fates established early in development) cleavage Deuterostomata Deuterostomata Protostomata Protostomata The deuterostomes: Echinoderms & Chordates The deuterostomes: Echinoderms and Chordates Deuterostome development : formation of mesoderm and coelom Blastopore forms anus, mouth forms secondarily , hence, deuterostomes ( deutero = second , stome = mouth ) Mesoderm begins to form from outpockets of the early gut: enterocoely ( from endoderm) The deuterostomes: Echinoderms and Chordates Porifera Cnidaria Platy- Nematoda Arthropoda Annelida Mollusca Echino- Chordata helminthes dermata levels of cell & tissue organization fundamental symmetry and number of germ layers development pattern the nature of the body cavity presence or absence of a body cavity Protostoma Deuterostoma Eucoelomates Pseudocoelomates other Bilateria Acoelomates Protistan ancestor Eumetazoa Parazoa Bilateria Radiata About 7,000 species, all marine substrate dwellers (larvae planktonic). Adults sedentary or slow-moving. Unique features (besides deuterostomate development) are: Pentaradial symmetry . After coelom formation, larva goes through a bilaterally symmetric stage which develops asymmetrically. Internal (dermal) skeleton (endoskeleton) made of ossicles of CaCO 3 . Movable in some species (spines). Internal water vascular system , derived from coelom. Used in locomotion and other functions. Connects to podia (short 'tentacles' or arms, often with grasping ends) -- also called tube feet . phylum Echinodermata Larval development very complicated. After coelom formation, larva is bilaterally symmetrical but develops asymmetrically: at early metamorphosis, left side of coelom grows, right side degenerates subsequently, coelom forms 5 branches that guide growth further growth and metamorphosis yields adult with secondary radial symmetry based on five body 'sectors': pentaradial symmetry phylum Echinodermata class ASTEROIDEA (sea stars) [ brittle stars are similar; crinoids resemble sea stars but have 'feathery' arms; may be sessile with stalks (sea lilies) or mobile (feather stars)] Most show pentaradial symmetry, with 5 arms (some have 20 or more arms): Central core madreporite arms Pyloric stomach Stone canal Pyloric cacae mouth Ring canal Radial canal Cardiac stomach Radial and ring canals, stone canal: water vascular system , opening to outside is madreporite...
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- Spring '07