Synapomorphy: plates 6, 7, 8, and 9 spreading into the fasciole in E.
Number of pore pairs of the frontal ambulacrum enclosed in the internal fasciole.
Arrangement of the ambulacral pores enclosed in the internal fasciole.
Architectural position of the fasciole within the frontal ambulacrum.
The resulting vector field [ILLUSTRATION FOR FIGURE 10 OMITTED] shows quite strong differences located along the outline of the test (frontal part; midline of interambulacra 1 and 4) and along the internal fasciole (lateral and posterior parts).
The peramorphosis corresponds to an architectural differentiation of the species that encompasses the belt of plates bearing the internal fasciole and the anterior ambulacrum.
Echinocardium laevigaster displays four pairs of ambulacral plates entering the subanal fasciole (character 12).