“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