RAH_20Lec_209_20__20Chordates

RAH_20Lec_209_20__20Chordates - Hough Lecture Outline -...

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Hough Lecture Outline - Chordates 1 CHORDATE BRANCH OF DEUTEROSTOMES TRANSITIONAL PHYLUM: HEMICHORDATA “Half chordates” - acorn worms similar to lobophorates (but no lobophore) two chordate characteristics: pharyngeal slits PHYLUM CHORDATA Four basic characteristics: 1. dorsal tubular nerve cord derived from ectoderm by invagination process similar t o gastrulation 2. notochord longitudinal supportive staff of dense mesoderm tissue (precurser of vertebral column) just below the nerve cord 3. pharyngeal slits series of vertical openings on each side of pharynx aid in filter feeding (precurser of housing of gills) 4. postanal tail nerve cord, notochord and musculature extending posterior t o the anal opening of the digestive tract NOTE : In some chordate species the pharyngeal slits and tail are not present in adults, but they are present in all chordate embryos (strong evidence for this evolutionary lineage).
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Hough Lecture Outline - Chordates 2 [TWO ACRANIATE (NO SKULL) SUBPHYLA:] I. Subphylum UROCHORDATA Tunicates small, simple marine invertebrates free-living larvae have all of the chordate characteristics adults have pharyngeal slits only; nerve cord and notochord disappear, along with most of the muscular body; barely bilateral, with no head adults have a thick, outer sac-like skin (the tunic) made of cellulose (very unusual for animals) some adults are sessile (attached) – sea squirt, sea peach some adults are planktonic – salps (many are bioluminescent) II. Subphylum CEPHALOCHORDATA Lancelets small fish-like marine invertebrates, with distinct head end some adults burrow tail end in sediment, filter feed retain all of chordate characteristics as adults precede vertebrates in fossil record, but living species have some proto-vertebrate characteristics in neuroembryology: genes for certain vertebrate brain regions proto neural crest cells proto “hypothalamus” cell cluster & limbic system
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Hough Lecture Outline - Chordates 3 [ONE CRANIATE (SKULL PRESENT) SUBPHYLUM:] III. Subphylum VERTEBRATA Vertebrates with skull vertebral column of cartilage or bone encasing the nerve cord (replaces notochord during development) endoskeleton (including vertebrae) of cartilage or bone (strong, but less brittle than chitin) distinct head with skull surrounding brain; trunk, tail regions complex skin tissue with accessories (e.g. scales, feathers, hair) ventral, strong heart and closed circulatory system unique internal organs including liver (many metabolic control functions) kidneys (one pair, advanced nephric) endocrine glands (ductless hormone producers) complex immune system – lymphocytes and phagocytes (invertebrates have phagocytes only) VERTEBRATE EVOLUTION Key features in the progressive evolution of the vertebrate classes involving comparative embryology and anatomy:
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RAH_20Lec_209_20__20Chordates - Hough Lecture Outline -...

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