ZOO 2090 Midterm Review.docx - ZOOLOGY MIDTERM REVIEW The...

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ZOOLOGY MIDTERM REVIEW The Origin of Chordates Why do organisms look the way they do? To understand a structure (morphology) Adaptation to a lifestyle or environment (link between structure and function) Ancestry: phylogenetic inertia Chordata and its close relatives Homologous characters share a common ancestry/derived from same ancestral structure o Human hands and bird wings homologous as forelimbs Analogous characters have same function but not necessarily same ancestry o Insect wing and bird wing Phylogeny is a genealogy (historical relationships) of species or higher taxa genera, families A group that includes the most recent common ancestor and ALL its descendants is a monophyletic group 7 levels of hierarchical classification o Kingdom: Animalia o Phylum: Chordata Subphylum: Vertebrata o Class: Mammalia o Order: Primates o Family: Hominidae Subfamily: Homininae o Genus: Homo o Species: sapiens Close Relatives of the Phylum Chordata linked by similar embryonic development: o Phylum Echinodermata (starfish etc.) o Phylum Hemichordata (acorn worms, etc.) Together the three phyla make up Deuterostoma, with Protostoma as its sister group Deuterostoma and Protostoma differ in embryological development Phylum Hemichordata (acorn worms) Considered closely related to chordates because they share pharyngeal slits Suspension feeders Burrowing marine worms that share larval and molecular characters with echinoderms Proboscis is used for locomotion and feeding (eating sediments or filter feed) ~ 90 species. Pterobranches – sessile adult colonies show modified enteropneust pattern o U shaped trunk so that anus opens at top of rigid tube in which they reside (live fixed in the ground)
Phylum Echinodermata Marine deuterostomes with radial symmetry as adults, bilateral symmetry as larvae Deuterostoma = “secondary mouths” o Blastopore (first opening) of the embryo becomes anus and a new opening is formed for the mouth Protostoma = “primary mouths” o Blastopore forms the mouth Phylum Chordata Subphylum: Urochordata notochord extends to tail Subphylum: Cephalochordata notochord extends to head Subphylum: Vertebrata notochord replaced by vertebrae 5 CHORDATE FEATURES 1. Notochord fluid-filled elastic rod dorsal to the gut tube and ventral to the nerve chord. Flexible sideways, but does not collapse Functions: keeps the body straight and prevents collapse during axial muscle contraction for movement. Promotes or organizes embryonic development of nearby structures Well developed in cephalochordates Fate: In most adult chordates, the notochord disappears or becomes highly modified its function is taken over by vertebral column in later forms 2. Dorsal, hollow nerve cord hollow tube formed by invagination at the surface of the ectoderm in embryo Gives rise to central nervous system Neural tube is dorsal to gut tube Contrast to invertebrates nerve cord is solid ventral to gut 3. Pharyngeal slits

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