Fig. 14 in New insights into the origin and relationships of blastoid echinoderms

Fig. 14. Subterminal branching in the ambulacra of the callocystitid Callocystites fresti Paul, 2015a (SM A.85652), Wenlock (Silurian), Indiana, USA. Open arrow points to the place where the next lateral branch of the radial water vessel would have taken place, but the tip of the radial water vessel was at the top of the brachiole (Br) that arose from the final facet (solid arrow). Thus, branching of the radial water vessel in brachiole-bearing echinoderms was always subterminal. Modified from Paul and Hotchkiss 2020: fig. 7.