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Ptychoderid hemichordate neurulation without a notochord
Shawn Luttrell1, Charlotte Konikoff, Alana Byrne
1Department of Biology, University of Washington, Seattle, WA 98195, USA.
Integrative and Comparative Biology
|September 12, 2012
Summary
Hemichordates and chordates show similar central nervous system (CNS) development, with hemichordates lacking a notochord but possessing a proboscis skeleton. This suggests the CNS may have evolved before the notochord.
Area of Science:
- Developmental Biology
- Evolutionary Biology
- Comparative Anatomy
Background:
- Enteropneust hemichordates share key traits with chordates, including a Hox-specified axis, pharyngeal slits, dorsal CNS, and a postanal tail.
- Ptychoderid hemichordates, like Ptychodera flava, exhibit feeding larvae and significant CNS regeneration capabilities.
Purpose of the Study:
- To compare neurulation and central nervous system (CNS) development between ptychoderid hemichordates and chordates.
- To investigate the evolutionary relationship between the notochord and the CNS in chordates and hemichordates.
Main Methods:
- Histological analyses were employed to compare neurulation processes.
- Comparative developmental studies focused on Ptychodera flava and chordate models.
Main Results:
- Similarities in central nervous system (CNS) development were observed between ptychoderid hemichordates and chordates.
- Ptychoderid hemichordates, lacking a notochord, develop a proboscis skeleton from endoderm post-neurulation.
- The proboscis skeleton's position suggests a structural role analogous to the chordate notochord.
Conclusions:
- The findings suggest that the central nervous system (CNS) may have preceded the evolution of the notochord.
- Alternatively, the notochord might have been lost in hemichordates.
- The notochord's evolutionary origin is ambiguous, possibly arising from endoderm rather than mesoderm.
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