Figure 7. Ophiopleura borealis postlarval development. A, B, 0.6 mm dd postlarva; A, dorsal, note the high disc, swollen lateral arm plates and dorsal madreporite; B, ventral, note ventral hydropore at madreporite tip (between ASs); C, 0.8 mm dd postlarva dorsal, secondary inter-radial plates have formed above the radial primary plates (IR0); D, E, 1 mm dd postlarva; D, dorsal, secondary radial plates (SRP) have formed above the radial primary plates; E, ventral, the madreporite is now ventral; F, 1.2 mm dd postlarva dorsal; G, H, 1.8 mm dd postlarva; G, dorsal, secondary inter-radial plates (IR2) have formed below the first inter-radial plates (IR1); H, ventral, a second mouth papilla has formed on the dental plate; I, J, 2.6 mm dd juvenile; I, dorsal, the k-plate separates the radial shields proximally; J, ventral; K–L, 5 mm dd juvenile; K, dorsal, note the thick skin on the disc only partly removed; L, ventral; M, arm lateral, note two widely spaced short arm spines; N, arm ventral. Abbreviations: as in Figs 1–3, 5. Scale bars in millimetres.