Fig. 5

CL and optical images of polished ossicles of Prionocidaris baculosa labeled with Mn²⁺ at 1 mg/L during the second marking experiments. a cross-section of an ambitus interambulacral plate in lateral view, b cross-section of a young interambulacral plate near the apical disc in meridional view, c cross-section of an ambitus interambulacral plates with enlarged central tubercle in lateral view, d lateral view of tooth near the proximal part of the shaft, e lateral view of tooth near the incisal end, f-i transverse cross-sections through a tooth (from the level near shaft/plumula boundary (∼7 mm from the adoral tip) towards the incisal end (∼5, 3 and 1 mm from the adoral tip, respectively)), j lateral view of a distal end of growing spine, k lateral view of a growing spines showing an initial phase of cortex formation at the middle height of the spine, l lateral view (at the middle height of the spine) of a growing spines showing later phase of cortex formation with enlargement of selected microregion, m-o cross-sections of a growing spine showing later phase of cortex formation (at the middle height of spine) under CL, optical and polarizing microscope views, respectively, p-s lateral views (at the middle height of spine) of a growing spine showing late phase of cortex formation. Abbreviations: Th - thickening increments, Res? - possible deposition of calcite on previously resorbed stereom, Ms - microspines, C - outer crust, Pb - pillar bridges, P - prisms, Pp - primary plates, L - lamellae, N - needles, Spi - spinule, Pro - protuberances, Sc - stromatic channels, Ic - inner cortex, Oc - outer cortex. Orange-red skeletal regions indicate enchanced Mn²⁺ concentrations due to Mn²⁺ labeling; dark regions indicate growth in normal (without Mn²⁺) seawater