Astriclypeidae, Stefanini, 1912

Ziegler, Alexander, Lenihan, Jennifer, Zachos, Louis G., Faber, Cornelius & Mooi, Rich, 2016, Comparative morphology and phylogenetic significance of Gregory’s diverticulum in sand dollars (Echinoidea: Clypeasteroida), Organisms Diversity & Evolution (New York, N. Y.) 16 (1), pp. 141-166 : 158

Astriclypeidae

This family is here represented by three extant and two fossil genera. Gregory’ s diverticulum could not be found in Astriclypeus mannii ( Fig. 5a–e ), Sculpsitechinus auritus ( Fig. 5f–j ), Sculpsitechinus tenuissimus , or Echinodiscus bisperforatus ( Fig. 5k–o ). The initial results based on X-ray imaging were supplemented by high-field MRI datasets, here shown in the form of virtual sections at the level of the main digestive tract ( Fig. 5e, j, o ). Although the observation that Gregory’ s diverticulum is absent in extant astriclypeid taxa is in conflict with the previous report that Gregory’ s diverticulum is present in E. bisperforatus ( Mooi and Chen 1996) , careful study of the rotatable 3D MRI datasets did not reveal any trace of the organ. Gregory’ s diverticulum also could not be seen in the fossil astriclypeid species Paraamphiope raimondii and Amphiope bioculata , as well as two further, yet unnamed fossil species of Amphiope .

elongated digestive tract. All images show an aboral view with ambulacrum III facing upwards. Streak artifacts in c and d caused by the use of X-ray-opaque paper cloth during scanning. in intestine, re rectum, st stomach. Scale bar = 1 mm

Figures

Fig. 5 Absence of Gregory’s diverticulum in the Astriclypeidae. The figure shows selected X-ray images as well as virtual MRI sections. a–e Astriclypeus mannii (9, 13, 16, 17.5, 16 mm test length); f–j Sculpsitechinus auritus (8, 11, 28, 30, 16 mm); and k–o Echinodiscus bisperforatus (12, 30, 31, 32, 15 mm). White arrows denote the area of the