Figure 7

Horizontal light-microscopic sections through the echinoid axial complex. A, B Eucidaris tribuloides (Cidaroida); C, D Diadema setosum (Diadematidae); E, F Psammechinus miliaris (Echinoida); G, H Echinocyamus pusillus (Clypeasteroida). Left column: section at the level of head process and dorsal sac. Right column: section at the level of axial organ and axial coelom. ac = axial coelom, ao = axial organ, dm = dorso-ventral mesentery, ds = dorsal sac, fm = free mesentery, go = gonad, hp = head process, ma = madreporic ampulla, oe = oesophagus, pv = pulsating vessel, re = rectum, sc = stone canal, so = somatocoel.