Fig. 3

CL and SEM images of Paracentrotus lividus labeled with Mn²⁺ at 1 mg/L during the second labeling experiment. a lateral view of a polished spine with enlarged microregion showing septa formation, b cross-section of a polished spine, c-e micromorphology of septa revealed after formic acid etching, f, g cross-sections showing lateral view of the polished tooth, h, i transverse cross-sections through the polished tooth (at the level of proximal shaft (∼6 mm from the aboral end and ∼8 mm from the adoral tip) and near the incisal end (∼11 mm from the aboral end and ∼3 mm from the adoral tip), respectively), j, k cross-sections near the polished ambital plates showing a contact between two test plates (adapical and interadial sutures, respectively). Abbreviations: Th - thickening increments, Pi - pore infilling deposit, Ms - microspines, Sb - stereom bridges, C - outer crust, Pb - pillar bridges, P - pisms, Cp - carinar process plates, Sp - secondary plates, Plb - plate boundary, L - lamellae, N - needles. Orange-red skeletal regions indicate enchanced Mn²⁺ concentrations due to Mn²⁺ labeling; dark regions indicate growth in normal (without Mn²⁺) seawater