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Lecture_11_Animals_II - Deuterostomes Animals II LS1 Summer...

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6/15/2011 1 Animals II LS1: Summer Session A July 18, 2011 Deuterostomes Deuterostomes are a diverse group of animals Exhibit radial cleavage During embryonic development, the blastopore develops into the anus Coelom develops from mesodermal pockets during gastrulation as opposed to the splitting of the mesoderm Deuterostome phylogeny Three major lineages of deuterostomes Echinoderms : which include sea stars, sea urchins, and relatives Hemichordates : including the acorn worms and pterobranchs Chordates : including sea squirts, lancelets, and vertebrates Origin of deuterostomes Recent fossil evidence (as well as DNA data) suggests that all deuterostomes evolves from an organism with pharyngeal slits and bilateral symmetry Echinoderms, therefore, likely reverted to radial symmetry secondarily Echinoderms Although radially symmetrical as adults, echinoderm larvae are bilateral, reflecting their descent from bilateral ancestors
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6/15/2011 2 Unique features of the echinoderms Echinoderms exhibit pentaradial symmetry, a calcified internal skeleton, and a water vascular system with tube feet . Echinoderm diversity The water vascular system is utilized in different ways in the different species of echinoderms. Hemichordates Wormlike, marine deuterostomes Have a proboscis, a collar, a pharynx with pharyngeal slits The Chordates The chordates consist of three principal clades: Cephalochordates Urochordates Vertebrates Chordate Features All share four features: 1. Notochord supports body 2. Nervous system develops from dorsal nerve cord 3. Embryos have pharynx with slits 4. Embryos have tail that extends past anus Chordate advantages 1.
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