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The A/P axis in echinoderm ontogeny and evolution: evidence from fossils and moleculesEven though echinoderms are members of the Bilateria, the location of their anterior/posterior axis has remained enigmatic. Here we propose a novel solution to the problem employing three lines of evidence: the expression of a posterior class Hox gene in the coeloms of the nascent adult body plan within the larva; the anatomy of certain early fossil echinoderms; and finally the relation between endoskeletal plate morphology and the associated coelomic tissues. All three lines of evidence converge on the same answer, namely that the location of the adult mouth is anterior, and the anterior/posterior axis runs from the mouth through the adult coelomic compartments. This axis then orients the animal such that there is but a single plane of symmetry dividing the animal into left and right halves. We tentatively hypothesize that this plane of symmetry is positioned along the dorsal/ventral axis. These axis identifications lead to the conclusion that the five ambulacra are not primary body axes, but instead are outgrowths from the central anterior/posterior axis. These identifications also shed insight into several other evolutionary mysteries of various echinoderm clades such as the independent evolution of bilateral symmetry in irregular echinoids, but do not elucidate the underlying mechanisms of the adult coelomic architecture.
Document ID
20040112514
Document Type
Reprint (Version printed in journal)
Authors
Peterson, K. J. (California Institute of Technology Pasadena 91125, United States)
Arenas-Mena, C.
Davidson, E. H.
Date Acquired
August 21, 2013
Publication Date
March 1, 2000
Publication Information
Publication: Evolution & development
Volume: 2
Issue: 2
ISSN: 1520-541X
Subject Category
Life Sciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Evolutionary Biology