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The A/P axis in echinoderm ontogeny and evolution: evidence from fossils and molecules

Peterson, Kevin J. and Arenas-Mena, César and Davidson, Eric H. (2000) The A/P axis in echinoderm ontogeny and evolution: evidence from fossils and molecules. Evolution & Development, 2 (2). pp. 93-101. ISSN 1520-541X. doi:10.1046/j.1525-142x.2000.00042.x.

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Even 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.

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Additional Information:© 2001 Blackwell Science, INC. Article first published online: 24 Dec 2001. We thank Bob Turring of the Graphic Arts Facility of Caltech for creating Figs. 2, 3A, and 5. We are grateful to many colleagues for discussions of these ideas, and in particular to Dr. Andrew Smith of the Natural History Museum (London), Dr. Jim Sprinkle of the University of Texas (Austin), Dr. Frederick Hotchkiss (Harvard, MA) especially for his help with Fig. 6, and to Drs. R. Andrew Cameron and James Coffman of this Division for critical review of the manuscript. This work was supported by a NASA Ames Life Sciences Grant (NAG2-1368), and by the Stowers Institute for Medical Research. K. J. P. was a Geobiology Postdoctoral Fellow of Caltech.
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Stowers Institute for Medical ResearchUNSPECIFIED
Caltech Geobiology Postdoctoral FellowshipUNSPECIFIED
Issue or Number:2
Record Number:CaltechAUTHORS:20160229-081834841
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Official Citation:Peterson, K. J., Arenas-Mena, C. and Davidson, E. H. (2000), The A/P axis in echinoderm ontogeny and evolution: evidence from fossils and molecules. Evolution & Development, 2: 93–101. doi: 10.1046/j.1525-142x.2000.00042.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64832
Deposited By: Ruth Sustaita
Deposited On:29 Feb 2016 17:49
Last Modified:10 Nov 2021 23:35

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