Organisms Diversity & Evolution

, Volume 16, Issue 1, pp 141–166 | Cite as

Comparative morphology and phylogenetic significance of Gregory’s diverticulum in sand dollars (Echinoidea: Clypeasteroida)

  • Alexander ZieglerEmail author
  • Jennifer Lenihan
  • Louis G. Zachos
  • Cornelius Faber
  • Rich Mooi
Original Article


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 cecum 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 100 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, microcomputed 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.


Echinodermata Digestive tract Gregory’s diverticulum Magnetite Comparative morphology Soft tissue Phylogeny 



Microcomputed tomography








British Museum of Natural History, London, UK


Bernice P. Bishop Museum, Honolulu, HI, USA


California Academy of Sciences Geology, San Francisco, CA, USA


California Academy of Sciences Invertebrate Zoology, San Francisco, CA, USA


Computed tomography


Florida Department of Natural Resources, St. Petersburg, FL, USA




Museum of Comparative Zoology, Cambridge, MA, USA


Misaki Marine Biological Station, Misaki, Japan


Muséum national d'Histoire naturelle, Paris, France


Magnetic resonance imaging


Million years ago


National Museum of Natural Science, Taipei, Taiwan


Scripps Institution of Oceanography, San Diego, CA, USA


Université de Bourgogne, Dijon, France


Museum of Paleontology, University of California, Berkeley, CA, USA


Museo de la Universidad Nacional Experimental Francisco de Miranda, Falcón, Venezuela


United States National Museum, Washington, DC, USA


University of Texas at Austin, Austin, TX, USA


University of Toronto, Ontario, Canada


Western Australian Museum, Perth, Western Australia, Australia


Museum für Naturkunde, Berlin, Germany


Zoologisches Museum Hamburg, Hamburg, Germany


Zoologisk Museum København, Copenhagen, Denmark


Zoologische Staatssammlung München, Munich, Germany



We would like to thank the following colleagues for providing access to museum specimens: Nadia Améziane (MNHN), Andrew Cabrinovic (BMNH), Jean DeMouthe (CASG), Mariko Kondo (MMBS), Kwen-Shen Lee (NMNS), Carsten Lüter (ZMB), Kelly Markello (CASIZ), Jørgen Olesen (ZMK), David L. Pawson (USNM), Chrissy Piotrowski (CASIZ), Bernhard Ruthensteiner (ZSM), Andreas Schmidt-Rhaesa (ZMH), and Robert M. Woollacott (MCZ). We are grateful to Felix Beckmann, Johannes Müller (ZMB), Nina Nagelmann, and Malte Ogurreck for their kind help with imaging equipment. Adam Baldinger (MCZ), Tom Schiøtte (ZMK), and Berit M. Ullrich provided valuable assistance with specimen handling and shipment. Constructive comments and suggestions by Andreas Kroh and one anonymous reviewer helped to improve the text. We are furthermore indebted to Gonzalo Giribet (MCZ) and Andreas Ziegler for facilitating access to scanning systems.

Supplementary material

13127_2015_231_MOESM1_ESM.pdf (6.4 mb)
ESM 1 (PDF 6.35 mb)


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Copyright information

© Gesellschaft für Biologische Systematik 2015

Authors and Affiliations

  • Alexander Ziegler
    • 1
    Email author
  • Jennifer Lenihan
    • 2
  • Louis G. Zachos
    • 3
  • Cornelius Faber
    • 4
  • Rich Mooi
    • 5
  1. 1.Institut für ZoologieRheinische Friedrich-Wilhelms-Universität BonnBonnGermany
  2. 2.Museum of Comparative Zoology, Department of Organismic and Evolutionary BiologyHarvard UniversityCambridgeUSA
  3. 3.Department of Geology and Geological EngineeringUniversity of MississippiOxfordUSA
  4. 4.Institut für Klinische RadiologieWestfälische Wilhelms-Universität MünsterMünsterGermany
  5. 5.California Academy of SciencesSan FranciscoUSA

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