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Zoology 250 (2017)
PROTOSTOMIA &
DEUTEROSTOMIA
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Two major divisions of the Bilateria (Protostomia and Deuterostomia) exhibit many differences:
- 1) Origin of mesoderm is from very different cell types:
- mesenchyme cells (non-epithelial) migrate in (Protostomia)
- epithelial cells inpocket from archenteron (Deuterostomia)
- 2) Origin of coelom is via two different mechanisms:
- enterocoely outpockets from archenteron close off and form enclosed, mesodermally lined coelom (Deuterostomia)
- schizocoely: mesenchyme cells proliferate into balls of cells that then 'split' to form mesodermally lined coelom (Protostomia)
- 3) Origins of mouth and anus differ. The blastopore gives rise to the:
- mouth; the anus arises secondarily (Protostomia)
- anus; the mouth arises secondarily (Deuterostomia)
- 4) Other differences include:
- PROTOSTOMIA:
- spiral and determinate cleavage
- multiciliated cells
- DEUTEROSTOMIA:
- radial and indeterminate cleavage (primitive state)
- monociliated (primitive state)
- 5) Membership in the Deuterostomia and Protostomia is in a state of flux:
- deuterostomes may only include echinoderms, hemichordates and chordates; the remaining bilaterian phyla may all be protostomes or be split into two groups: protostomes and lophophorates (stay tuned!)
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Copyright (c) 2017 by A. Richard Palmer. All rights reserved.
(revised Dec. 19, 2016)