The formation of the sea urchin calcareous embryonic skeleton occurs in
specialized vesicles/vacuoles within the PMCs. Cells tightly control the concentration of the ions precursors and nucleation is initiated by deposition on an organic
template. The pH, pCO 2 , and the concentration of trace elements are regulated by
Fig. 8.2 Schematic drawing the location and arrangements of PMCs. (a) Gastrula frontal and
vegetal views showing the PMCs aggregates (clusters) at opposite sides of the archenteron and one
of the clusters enclosing the spicule triradiate rudiment; (b) formation of PMCs aggregates and
initial pseudopodial fusion; (c) alignment of PMCs and enlargement of the fused cytoplamic space,
note the first sign (white dot) of biomineral deposition; and (d) development of spicule rudiment
inside the cell cluster (white area), assuming the shape of a triradiate crystal (modified from
Dubois and Chen 1989)
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V. Matranga et al.
specialized vesicles/vacuoles within the PMCs. Cells tightly control the concentration of the ions precursors and nucleation is initiated by deposition on an organic
template. The pH, pCO 2 , and the concentration of trace elements are regulated by
Fig. 8.2 Schematic drawing the location and arrangements of PMCs. (a) Gastrula frontal and
vegetal views showing the PMCs aggregates (clusters) at opposite sides of the archenteron and one
of the clusters enclosing the spicule triradiate rudiment; (b) formation of PMCs aggregates and
initial pseudopodial fusion; (c) alignment of PMCs and enlargement of the fused cytoplamic space,
note the first sign (white dot) of biomineral deposition; and (d) development of spicule rudiment
inside the cell cluster (white area), assuming the shape of a triradiate crystal (modified from
Dubois and Chen 1989)
232
V. Matranga et al.