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12 Cards in this Set
- Front
- Back
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Simple Metazoan Characteristics
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Multicellular
Blastula forms during embryonic development Sex cells formed in specialized organs Male gametes (sperm) have flagella |
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More derived metazoans
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Bodies composed of two distinct germ layers (diploblastic): ectoderm and endoderm
Gut with single opening Nervous tissue |
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Yet more derived metazoans
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bodies composed of three distinct germ layers (triploblastic): ectoderm, mesoderm, endoderm
Gut open at both ends |
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Even more derived metazoans
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Exhibit coelom
Two lineages: protostomes and deuterostomes |
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Protostome development
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Lineage of very derived metazoans
Ancestral condition Mouth develops first, anus second |
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Deuterostome development
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Lineage of very derived metazoans
Derived condition Mouth develops second, anus first Pattern exhibited by echinoderms, hemichordates and chordates |
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Phylum Chordata
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Monophyletic
Includes: subphylum urochordata (tunicate) subphylum cephalochordata Craniata: subphylum Vertebrata |
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Phylum Chordata characteristics
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Notochord (stiff, longitudinal rod)
Nerve cord (tubular and dorsal notochord) Postanal tail (as a larva or embryo) Endostyle (groove on pharyngeal floor) Pharyngeal pouches (may be plesiomorphic--same as ancestral) |
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Nonvertebrate Chordates
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Urochordates (sea squirts)
Cephalocordates (lancelet/amphioxus) Cambrian Chordates: Pikaia, Vetulicolians (Xidazoon), Yunnanozoans (Haikouella) |
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Urochordates
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Tunicates/sea squirts
Marine Filter feeders Most adults sedentary Larval form most like ancestral chordate Secondarily lost chordate characteristics |
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Cephalochordate characteristics
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(lancelet/amphioxus)
Marine Filter feeders Adults burro, but capable of swimming Possess myomeres (apomorphic-changed from ancestral condition)--segments of striated muscle Swim by lateral undulations Possess atrium (plesiomorphic: has not changed from ancestral condition) Circulatory system with dorsal aorta and ventral heart (apomorphic) Excretory cells called podocytes (apomorphic) |
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Cambrian chordates
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Pikaia:
Possess myomeres Possess a notochord Possible cephalochordate Vetulicolians (Xidazon): Possess endostyle and pharyngeal gill slits Possible segmentation Lack a notochord Yunnanozoans (Haikouella): Possess myomeres, notochord, pharynx with atrium Exhibit many derived characeristics Possible sister group to vertebrates |
