Fig. 4

CL images of polished ossicles of Echinometra sp. labeled with Mn²⁺ at 1 mg/L during the second labeling experiments. a-d transverse cross-sections through a tooth (from the level near shaft/plumula boundary (∼8 mm from the adoral tip) towards the incisal end (∼6, 4 and 2 mm from the adoral tip, respectively)), e lateral view of tooth near the proximal part of shaft, f cross-section of an ambital interambulacral plate in lateral view, g cross-section near an ambitus showing a contact (adapical suture) between two test plates, h lateral view of a growing spine. Abbreviations: 1st, 2nd, 3rd - successive labeling events (indicated by solid arrows); R - interlabeling recovery, C - outer crust, Pb - pillar bridges, P - pisms, Cp - carinar process plates, Sp - secondary plates, St - stone part, Pp - primary plates, Plb - plate boundary, L - lamellae, N - needles. Orange-red skeletal regions indicate enhanced Mn²⁺ concentrations due to Mn²⁺ labeling; dark regions indicate growth in normal (without Mn²⁺) seawater