the chordate phylum chordate phylum: 6 vertebrate and 2 invertebrate classes, all having a similar...
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The Chordate PhylumChordate phylum: 6 vertebrate and 2 invertebrate classes, all having a similar set of 25,000 genes
Chordates: 6 vertebrate classes
Class: Birds. Hornbill
Class: Mammals. Mouse Class: Mammals. MandrillClass: Mammals.Monotremes; Echidna
Class: Reptiles. Bardick snake Class: Birds. Hummingbird
Phylum: Chordates. 6 vertebrate classes
Class: Jawless fish. Hagfish Class: Bony fish. Teleost. Anemone fish
Class: Amphibia. Xenopus tadpolesClass: Bony fish. Coelacanth
Class: Cartilaginous fish. Ratfish, Chimera
Invertebrate chordates: 2 classes
Phylum: Echinoderms. Starfish
Phylum: Chordates. Class: Urochordates; Ascidians
Phylum: Hemichordates; Class: Enteropneust
Phylum: Chordates. Class: Cephalochordates
posterior
anterior
Nearest phyla to chordates
Chordates and Arthropods are descended from a pre-Cambrian bilateral ancestor; as are the
other 24 bilateral phyla
Stages of Xenopus development
4-cell stage, 2.5 hrFertilized egg, 30 min.
Unfertilized eggs, in jelly coatsOocytes in the ovary. Note blood vessels
Spermentrypoint
Greycrescent
Stages of Xenopus development
Tadpoles, 2 weeks old, feeding
Late gastrula, 16 hr
Late neurula, 30 hr
Late blastula, 9 hr. About 8000 cells
Neural folds
Blastoporealmostclosed
Animalpole view
Phylotypic stage(pharylgula/tailbud stage): first embryonic stage to possess the main chordate traits, and an
“adult”map of >200 gene expression domains covering the 3 germ layers
(all preceding organs and cell types)