phylum chordata - york college of pennsylvaniafaculty.ycp.edu/~brehnber/bio 302...
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“Pre-Cambrian”
produced only
unicellular organisms
THE CAMBRIAN EXPLOSION
All major phyla including
Phylum Chordata
Geologic Time Scale
Origin of Species
(Chapter IX)
On the Imperfection of the Geologic Record
“There is another and allied difficulty, which is
much graver. I allude to the manner in which
numbers of species of the same group , suddenly
appear in the lowest known fossiliferous rocks.”
Darwin was aware …
5 CHORDATE CHARACTERISTICS
1) Notochord – present in embryonic, larval or adult stages
Not Cartilage!!
Large fluid-filled cells
having turgor pressure
Embryos
During pharyngeal development,
outside ectoderm invaginates …
inside endoderm evaginates
SLIT formation?
3) PHARYNGEAL POUCHES & CLEFTS
Tetrapod Vertebrates
Pouches form … but slits don’t break through.
Pouches develop into …
middle ear cavity
eustachian tube
tonsils
parathyroid glands
5) ENDOSTYLE or THYROID GLAND
CHORDATE CHARACTERISTICS continued …
Strip of tissue on the floor of the pharynx – secretes sticky mucus that
traps food from “inhaled” water.
In vertebrates, the thyroid gland develops in place of the endostyle.
Subphylum Urochordata
Subphylum Cephalochordata
Subphylum Vertebrata
All Oceans
Most Depths
1600 species
http://www.flickr.com/photos/nuytsia_pix/3130748320/
(secretes mucus)
(lined with ciliated cells)
ODD?
Closed circulatory system … BUT …
- no distinction between arteries & veins
- no capillaries
- blood flows forward & back
ODD?
*super-high tissue concentrations
of vanadium & niobium
*tunic contains cellulose
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