Fig. 1 in New insights into the origin and relationships of blastoid echinoderms

Fig. 1. Growth zone of ambulacrum B in the irregular echinoid Echinocyamus bisexus Kier, 1968, Eocene, Georgia, USA. An echinoid growth zone consists of four columns of plates, two central ambulacral columns the plates of which alternate, flanked by single columns of interambulacral plates (light grey shading). All the plates of a growth zone are added adjacent to the ocular plate at the aboral tip of each ambulacrum (on the opposite surface of the echinoid). The first two ambulacral plates to form during growth, the basicoronal plates adjacent to the mouth (M), express Lovén's Law. A, B, C, D, E, Carpenter's (1884, 1891) ambulacra; An, anus; H, hydropore (madreporite) on the opposite surface of the echinoid; L, left; R, right, designate ambulacral columns; M, mouth. Modified from Paul and Hotchkiss 2020: fig. 3.