“Seen in the light of evolution, biology is, perhaps, intellectually the most satisfying and inspiring science. Without that light it becomes a pile of sundry facts some of them interesting or curious but making no meaningful picture as a whole.” Dobzhansky 1973 How do these taxa relate? • • • • • • Radiata Ecdysozoa Deuterostomata Bilateria Lophotrochozoa Protostomata How do these embryological features relate to Deuterostomes and Protostomes? • Radial cleavage • Spiral cleavage • Blastopore => mouth • Blastopore => anus • Enterocoely • Schizocoely Basal Deuterostomes Haeckel 1874, proposed phylum “Chordata” and 3 subphyla: __________________ __________________ __________________ (includes Hagfish) Basal Deuterostomes Hypothesis that vertebrates and these “protochordates” share common ancestor provides impetus for study What features do these larvae share? How are they unique? Basal Deuterostomes ____________ (sea stars and allies) In fossil record from Cambrian to present 20 classes… today representatives of 5 Unique features: * * So why would they be considered “more closely related” than other marine invertebrates… say clam worms? http://www.palaeos.com/Invertebrates/Deuterostomia/Homalozoa/Images/Syringocrinus.gif Basal Deuterostomes __________________ (acorn worms) * Bateson 1884, proposed Hemichordata as a subgroup of Chordata http://www.wildsingapore.com.sg/wildfilms/blog/050402cjd2070m3a.jpg http://coris.noaa.gov/glossary/hemichordate_186.jpg Basal Deuterostomes Hemichordata (acorn worms) 2-3 possibilities for taxonomic placement: *Sister group to… *Sister group of… *Undetermined status (incertae sedis) http://www.geol.umd.edu/~tholtz/G331/lectures/331grapt.html Basal Deuterostomes Features shared by echinoderms and hemichordates: *Similar _____________ (bipinnaria and tornaria) *Muscle proteins *Nervous system structure Features linking to chordates: *____________ system http://scaa.usask.ca/gallery/lacalli/images/tornaria3.jpg * http://scaa.usask.ca/gallery/lacalli/images/cucumber5.jpg Urochordates Filter-feeding marine organisms divided into 3 classes: *___________ (tunicates or “sea squirts”) Larva are free-swimming but short-lived +/- phototaxis? Non-feeding larva metamorphosis Adults respire and feed using: * * Endostyle sends food to esophagus, then stomach http://www.youtube.com/watch?v=mecEpYS2Bgw Urochordates Filter-feeding marine organisms divided into 3 classes: * Free-swimming plankton Large mucus tunic http://homepage.mac.com/a.shiroza/pictures/planktons/ bwttf/larvatian1p2_x50.jpg Urochordates Filter-feeding marine organisms divided into 3 classes: *___________ (“salps”) Alternation of generations (free-living and colonial) No notochord… so why in phylum chordata? http://chemistry.csudh.edu/faculty/jim/cantamar/salp.jpg http://www.youtube.com/watch?v=KRVdGam3G2U&NR=1 Cephalochordates “Amphioxus” or “Lancelets” 2 genera: *Branchiostoma *Asymmetron Marine organisms found in coarse, sandy substrates http://comenius.susqu.edu/bi/202/Animals/DEUTEROSTOMES/cephalochordata/uwinnipegLancelet.jpg Cephalochordates Brief survey of systems: Musculature and integument: Mostly all trunk Metamerism (myomeres) Myoseptum Muscle fibers uninucleate Single cell layer epidermis Thin dermis Advantages of thin skin? Cephalochordates Pharyngeal slits: Exit to an internal chamber (___________) Filtered water leaves via… Slow moving water, high metabolic demands of cilia cells, and vasculature in collagen minimizes respiratory usefulness Cephalochordates “Skeletal” Notochord: “Muscular” notochord more apropo Muscular discs encased in sheath __________ ___________ rather than neurons Notochord to rostrum adaptation for burrowing Other “skeletal” elements include: fibrous rods in… Cephalochordates Nervous system 2 part brain rather than 3 Many cranial nerves (38 vs. 10-18) Spinal nerves with dorsal root only conducting sensory (________) signals to spinal cord and brain ________________, __________________ and ________________ Cephalochordates Nervous system Why such a small brain? * * * * Abundant chemoreceptors on cirri and tentacles… WHY? Tail also abundant Cephalochordates Digestive system ______________ ______ _____ coarse filter, monitor water _________ bounded by oral hood and velum Mouth opens to _____ _____ ______ picks up “chunks” http://www.uta.edu/studentorgs/pdsa/chordata.htm _____________ create flow and mucus Moves to midgut to mix with enzymes Intestinal cecum (“____________”) http://www.uta.edu/studentorgs/pdsa/chordata.htm Cephalochordates Circulatory system No ______ No ________ No _______________ Sinus venosus Cecal vein assists by pumping to sinus Cephalochordates Excretory system No _____________ ______________ (between protonephridia and podocytes) Pedicels surround ___________ __________ extend to nephridial tubule Wastes leave ____________ Cephalochordates Reproductive system _____________ Gonads (ovaries OR testes) empty sex cells (eggs OR sperm) into atrium, leaving via atriopore Cephalochordates Compare - Contrast limited cephalization No ________________________ No ________________________ 2 instead of 3 brain parts 2 layered skin (1 cell thick) No __________________ Greatly reduced coelom BUT many synapomorphies Origin of craniates So how do we get a vertebrate from an invertebrate? From annelid or arthropod-like ancestor?!? From a ribbon worm ancestor?!? http://www.idratherbewriting.com/wpcontent/uploads/2007/07/grasshopper.jpg From a sea cucumber?!? From an inverted acorn worm?!? http://northislandexplorer.com/worms/orangeribbonwork.jpg http://www.stanford.edu/~bhackett/monterey-2005-02-04/images/california-sea-cucumber.jpg http://www.bethel.edu/~johgre/bio114d/image s/Lower%20Verts/oAcornWorm.jpg