| Zoology 250 (2002) PROTOSTOMIA & DEUTEROSTOMIA (click on tree to see full cladogram) |
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Two major divisions of the Bilateria (Protostomia & 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:
- schizocoely: mesenchyme cells proliferate into balls of cells that then 'split' to form mesodermally lined coelom (Protostomia)
- enterocoely outpockets from archenteron close off and form enclosed, mesodermally lined coelom (Deuterostomia)
- 3) Origins of mouth & 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 & determinate cleavage
- multiciliated cells
- trochophore-like larva
- DEUTEROSTOMIA:
- radial & indeterminate cleavage (primitive state)
- monociliated (primitively)
- larva not trochophore-like
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Copyright © 2002 by A. Richard Palmer. All rights reserved.
(revised Feb. 3, 2002)