Exam 1 Chapter 2: Protochordates and Chordate Origins Flashcards
(28 cards)
Define protostome development
- spiral cleavage, blastopore becomes mouth
- mesoderm origin in mesentoblasts
Define deuterostome development
- Radial Cleavage, blastopore becomes anus
- origin of mesoderm from blastomeres
Name the five basic chordates characteristics
- notochord, pharyngeal slits, endostyle/thyroid, Dorsal hollow nerve cord, postanal tail
Notochord
chord bendable(so laterally flexible), but not compressible (resists shortening in length); lies along the path of the dorsal hollow nerve cord
o Without a notochord, lateral muscle contraction telescopes the body uselessly
o Notochord prevents collapse of the body - muscle contractions on alternating sides flex the body
Pharyngeal Slits
o Start in pouch form (pouch on one side, slide on other)
o Contributes to filter feeding, through front and items sucked out through slits
Endostyle/thryoid
- endostyle provides filter feeding
- thryoid regulates metabolism, effects bodily organs
Dorsal hollow nerve cord
on top of notochord, provides skeletal support and movement
Postanal tail
source of locomotion
In deuterostomes, which of the following groups are informally called “protochordates”?
o Hemichordata
o Chordates (Cephalochordata)
o Urochordata
o Vertebrata
Groups in Ambulacraria
- hemichordata, echinodermata
Echinodermata
o Echinoderms (“spiny-skins”) are named for the spines or spikes observed in many species
o All echinoderms are marine animals
o Bilateral as young, become radial later in development
o Deuterostomes, makes them closer to chordates
Examples: Seastars, starfish, sea urchins, anemones
Hemichordata
Enteropneusta and Pterobranchia
Enteropneusta
- acorn worms
o One chordate trait: pharyngeal slits
Pterobranchia
pterobranchs: tiny, attaches to surfaces, secrete carbohydrate tube(s)
One chordate trait: pharyngeal slits
Groups in Chordata
- Cephalochordata, Urochordata
In cephalochordata, what is the function of the wheel organ?
- Coordinate motion of cilia on whell organ create a flow of water, food particles trapped in mucus; major ciliated food corridors line the pharynx
- Has all 5 chordate characteristics
groups in Urochordata
- Ascidians and Larvaceans
How does metamorphosis affect the 5 chordate characteristics in Acidians?
All 5 exist in larvae
Notochord and nerve cord shrink and transform into something else, disappears
Only maintains endostyle
Larvaceans
o Have all five chordate characteristics, retain them all
The origin of chordates
Annelid/Arhtropod Hypothesis and Auricularian (echinoderm) hypothesis
Annelid/Arhtropod hypothesis
- both segmented with similar nervous and blood systems
explains chordate origins by the segmentation seen in the organisms along their spinal cord
Auricularian Hypothesis
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proposed fate of the circumoral ciliated bands?
Circumoral ciliated bands (and underlying nerves) moved dorsally to meet and fuse at the dorsal midline - dorsal nerve cord
proposed fate of adoral ciliated band?
Adoral ciliated band gave rise to the endostyle and ciliated tracts inside the pharynx
