“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

Origin of craniates

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