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Lecture 1-Phylogeny and Classification

Lecture 1-Phylogeny and Classification - Phylogeny and...

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Phylogeny and Classification August 27, 2007 to September 14, 2007 Phylum Chordata (Chordates) o Craniates and “Protochordates” Three major groups of chordates Tunicates-Urochordata “Uro”-tail Earliest chordates Lancelets-Cephalochordata “Cephalo”-head Elaborate front end/anterior elaboration Craniates-Craniata Includes vertebrates Are chordates “Crania”-brain case that covers brain Hagfish are craniates but not vertebrates since they do not have vertebrae o Thus, the craniates consist of hagfish and vertebrates o Chordata Characteristics Characteristic-any feature or attribute Non-exclusive characteristics-attributes chordates and other animals share; not only in chordates o Eukaryotic-have a true nucleus Archae and Bacteria do not have one o Have muscular tissue o Triploblastic-have three primary germ layers (ectoderm, mesoderm, endoderm) “Triplo”-three “Blast”-immature Immature organisms show three layers (gastrula) Nearly all animals are triploblastic o Eucoelomate-having a mesoderm lined coelem Coelem-main body cavity in organisms that house organs “Coelo”-body cavity “Eu”-true o Metameric-having segmental structure “Meta”-many/series “Mer”-unit Worms are not metameric o Pharyngeal patches or slits-pockets or holes in the throat “Pharynx”-throat Hemichordates are the only other group with pharyngeal slits; chordates are probably closely related and form a clade with hemichordates Exclusive characteristics-only chordates have them o Dorsal (back) hollow nerve cord As opposed to a solid ventral cord o Notochord Lies ventral (belly) to the nerve cord Induces nerve cord formation Many chordates lack it in adulthood o Subpharyngeal gland-located below throat Embryonic outgrowth of pharynx/throat Takes two forms in chordata Endostyle-mucus secreting gland present in eurochordates, cephalochordates, and the larval form of lamprey fish Thyroid-produces hormone thyroxin o Thyroxin influences the rates of cell metabolism Both are similar: 1
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In development and position (ventral…under…to throat) In that they have chemical products containing iodine (very rare in bodies) Since in lamprey the larva endostyle is converted to the adult thyroid THUS, the endostyle and the thyroid are probably homologous Because the endostyle is found in more basal organisms and lamprey fish larvae’s endostyles evolve into the thyroid, the thyroid probably evolved from the endostyle See generalized chordate diagram (blue handout)-know in detail General characteristics o Buccal cavity-oral cavity; non-exclusive to chordates o Gut-non-exclusive o Caudal region-tail region; exclusive o Pharyngeal arches-region of the wall of the pharynx between pharyngeal pouches/gill slits; non-exclusive due to hemichordates The “Protochordates” o Urochordata
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