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“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 DeuterostomesHaeckel 1874, proposed phylum “Chordata” and 3 subphyla:
__________________
__________________
__________________ (includes Hagfish)
Basal DeuterostomesHypothesis 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 DeuterostomesHemichordata (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 DeuterostomesFeatures 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
UrochordatesFilter-feeding marine organisms divided into 3 classes:
*___________ (tunicates or “sea squirts”)
Larva are free-swimming but short-lived
Non-feeding larva metamorphosis
Adults respire and feed using:
* *
Endostyle sends food to esophagus, then stomach
http://www.youtube.com/watch?v=mecEpYS2Bgw
+/- phototaxis?
UrochordatesFilter-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
UrochordatesFilter-feeding marine organisms divided into 3 classes:
*___________ (“salps”)
Alternation of generations (free-living and colonial)
No notochord… so why in phylum chordata?
http://www.youtube.com/watch?v=KRVdGam3G2U&NR=1
http://chemistry.csudh.edu/faculty/jim/cantamar/salp.jpg
Cephalochordates“Amphioxus” or “Lancelets”
2 genera:*Branchiostoma *Asymmetron
Marine organisms found in coarse,sandy substrates
http://comenius.susqu.edu/bi/202/Animals/DEUTEROSTOMES/cephalochordata/uwinnipeg-Lancelet.jpg
CephalochordatesBrief 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?
CephalochordatesPharyngeal 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…
CephalochordatesNervous system
2 part brain rather than 3
Many cranial nerves (38 vs. 10-18)
Spinal nerves with dorsal root onlyconducting sensory (________) signals to spinal cord and brain
________________, __________________ and ________________
CephalochordatesNervous system
Why such a small brain?
****
Abundant chemoreceptorson cirri and tentacles… WHY?
Tail also abundant
CephalochordatesDigestive 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
http://www.uta.edu/studentorgs/pdsa/chordata.htm
_____________ create flow and mucus
Moves to midgut to mix with enzymes
Intestinal cecum (“____________”)
CephalochordatesCirculatory system
No ______
No ________
No _______________
Sinus venosus
Cecal vein assists by pumping to sinus
CephalochordatesExcretory system
No _____________
______________ (between protonephridia and podocytes)
Pedicels surround ___________
__________ extend to nephridial tubule
Wastes leave ____________
CephalochordatesReproductive system
_____________
Gonads (ovaries OR testes)empty sex cells (eggs OR sperm) into atrium,leaving via atriopore
CephalochordatesCompare - Contrast
limited cephalization
No ________________________
No ________________________
2 instead of 3 brain parts
2 layered skin (1 cell thick)
No __________________
Greatly reduced coelom
BUT many synapomorphies
So how do we get a vertebrate from an invertebrate?
From annelid or arthropod-like ancestor?!?
From a ribbon worm ancestor?!?
From a sea cucumber?!?
From an inverted acorn worm?!?
http://www.stanford.edu/~bhackett/monterey-2005-02-04/images/california-sea-cucumber.jpg
http://www.idratherbewriting.com/wp-content/uploads/2007/07/grasshopper.jpg
http://northislandexplorer.com/worms/orangeribbonwork.jpg
http://www.bethel.edu/~johgre/bio114d/images/Lower%20Verts/oAcornWorm.jpg