Echinarachniidae, Lambert & Thiery, 1914

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 : 156

Echinarachniidae

Data from the following extant and fossil echinarachniid genera were incorporated into this study: Echinarachnius ( Fig. 3k–o ), Kewia ( Fig. 3p–s ), and Scutellaster ( Fig. 3t ). Gregory’ s diverticulum was identified in all echinarachniid taxa analyzed. A relatively comprehensive X-ray imaging series is available for Echinarachnius parma (4–62 mm). In this species, Gregory’ s diverticulum was found to be fully distended with sand up to a test length of 20 mm, while remnants of the organ could still be discerned up to a test length of 23 mm. In 32 out of 40 specimens of Echinarachnius (80 %) and 20 out of 20 specimens of Kewia (100 %), sediment was found inside the diverticulum.

Figures

Fig. 3 Absence of Gregory’s diverticulum in the Rolutidae (a–e) as well as presence and shape of the organ in the Taiwanasteridae (f–j) and Echinarachniidae (k–t). The figure shows selected X-ray images. a, b Heliophora orbicularis (15, 46 mm test length); c–e Rotula deciesdigitatus (17, 22, 50 mm); f–j Sinaechinocyamus mai (1.5, 3.5, 6, 6.5, 7.5 mm); k–o