Project 2202: A. Ziegler, J. Lenihan, L. G. Zachos, C. Faber, R. Mooi. Comparative morphology and phylogenetic significance of Gregory's diverticulum in sand dollars (Echinoidea: Clypeasteroida). Organisms Diversity & Evolution. (In Press)
Specimen: Mellita grantii (USNM:E26597)

Abstract

Several derived sand dollar (Echinoidea: Clypeasteroida) families are characterized by the presence of Gregory's diverticulum, an accessory organ of the digestive tract. This soft tissue structure is composed of a central tubular caecum that gives off multiple lobes into the periphery of the test. Most notable are the organ's capacity to selectively store sand grains that the animal has taken up from the surrounding sediment as well as the gradual reduction of Gregory's diverticulum during ontogeny. Several aspects of the biology of this structure have remained unexplored, including the organ's precise morphology and structural diversity. In order to provide a concise basis for future histological, physiological, and functional analyses, a comprehensive comparative morphological and phylogenetic study across numerous taxa was undertaken. Taxon sampling comprised over one hundred clypeasteroid species, including various fossil taxa. This extensive dataset permits establishing a concise terminology that incorporates all of the organ's substructures. In addition, three-dimensional models of Gregory's diverticulum are presented that provide an improved spatial understanding of the organ's morphology in situ. The combined data from dissection, X-ray imaging, micro-computed tomography, and magnetic resonance imaging reveal a previously unknown variability of the structure, which also yields several phylogenetically informative morphological characters. Among those sand dollar families that possess Gregory's diverticulum, the organ is present in two distinct shapes, which can be distinguished by the number, shape, and location of substructures. In addition, the data provide unequivocal evidence that Gregory's diverticulum is absent in the extant taxa Rotulidae and Astriclypeidae, but also in the enigmatic Marginoproctus.


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Article DOI: 10.1007/s13127-015-0231-9

Project DOI: 10.7934/P2202, http://dx.doi.org/10.7934/P2202
This project contains
  • 262 Media
  • 46 Taxa
  • 95 Specimens
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    Members

    member name taxa specimens media media
    notes
    Alexander Ziegler
    Project Administrator
    Last logged in 08/04/15
    4695262262
    Cornelius Faber
    Full membership
    Last logged in 07/05/15
    0000
    Seth Kaufman
    Full membership
    Last logged in 08/04/15
    0000
    Jennifer Lenihan
    Full membership
    Last logged in 06/26/15
    0000
    Rich Mooi
    Full membership
    Last logged in 06/29/15
    0000
    Louis G. Zachos
    Full membership
    Last logged in Never
    0000


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