The Echinoid Directory

Phormosoma placenta Wyville Thomson, 1872. Detail of apical disc (one genital and two ocular plates) and oral and adapical ambulacral plating. All from Mortensen, T. 1935. A monograph of the Echinoidea. Volume 2, Bothriocidaroida, Melonechinoida, Lepidocentroida and Stirodonta. C.A. Reitzel, Copenhagen (text-figs 80, 81).