The phylogeny of invertebrates and the evolution of myelin.
Current concepts of invertebrate phylogeny are reviewed. Annelida and Arthropoda, previously regarded as closely related, are now placed in separate clades. Myelin, a sheath of multiple layers of membranes around nerve axons, is found in members of the Annelida, Arthropoda and Chordata. The structure, composition and function of the sheaths in Annelida and Arthropoda are examined and evidence for the separate evolutionary origins of myelin in the three clades is presented. That myelin has arisen independently at least three times, namely in Annelids, Arthropodas and Chordates, provides a remarkable example of convergent evolution.
Roots
Betty I
BI
Department of Cell and Systems Biology, University of Toronto, Ontario, Canada. betty.roots@utoronto.ca
D000818:Animals; D000845:Annelida; D001181:Arthropods; D004594:Electrophysiology; D019143:Evolution, Molecular; D007448:Invertebrates / Q000235:genetics* / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D008055:Lipids / Q000032:analysis; D008854:Microscopy, Electron; D009185:Myelin Proteins / Q000032:analysis; D009186:Myelin Sheath / Q000737:chemistry / Q000235:genetics* / Q000648:ultrastructure; D009412:Nerve Fibers / Q000502:physiology; D009431:Neural Conduction; D010802:Phylogeny; D013997:Time Factors
D008055:Lipids; D009185:Myelin Proteins