Fig. 2

CL images of polished sea urchin spines labeled during trial marking experiments. a lateral view with enlarged microregion of a spine showing regenerated tip of Paracentrotus lividus labeled with Mn²⁺ at 1 mg/L, b lateral view with enlarged microregion of a spine showing regenerated tip of Paracentrotus lividus labeled with Mn²⁺ at 3 mg/L, c lateral view of spine showing a regenerated tip of Echinometra sp. labeled with Mn²⁺ at 3 mg/L, d cross-section of a regenerated tip of spine of Echinometra sp. labeled with Mn²⁺ at 3 mg/L. Abbreviations: Th - thickening increments, Pi - pore infilling deposit Fr - cutting fracture (delineated with dotted line). Orange-red skeletal regions indicate enhanced Mn²⁺ concentrations due to twice Mn²⁺ labeling; dark regions indicate growth in normal (without Mn²⁺) seawater