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What ions do sea urchins use to build their skeletons?
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Sea urchin skeletons are made of calcium carbonate. The key ions are:
- Ca2+ (calcium) — the main cation.
- CO3 2− (carbonate) — the anion that combines with Ca2+ to form CaCO3. In seawater most dissolved inorganic carbon is HCO3− (bicarbonate), which animals convert (often with carbonic anhydrase and bicarbonate transporters) into carbonate for mineralization.
- Mg2+ (magnesium) — incorporated into the crystal lattice to produce high‑magnesium calcite (common in echinoderms). Small amounts of Sr2+ and other trace ions can substitute as well.
Many urchins first deposit amorphous calcium carbonate (ACC, loaded with Mg) as a precursor that later crystallizes into Mg‑calcite.
- Ca2+ (calcium) — the main cation.
- CO3 2− (carbonate) — the anion that combines with Ca2+ to form CaCO3. In seawater most dissolved inorganic carbon is HCO3− (bicarbonate), which animals convert (often with carbonic anhydrase and bicarbonate transporters) into carbonate for mineralization.
- Mg2+ (magnesium) — incorporated into the crystal lattice to produce high‑magnesium calcite (common in echinoderms). Small amounts of Sr2+ and other trace ions can substitute as well.
Many urchins first deposit amorphous calcium carbonate (ACC, loaded with Mg) as a precursor that later crystallizes into Mg‑calcite.
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