animals with hard external skeletons like crabs, lobsters, and shrimp that live mostly in water.
From Latin crusta (shell or crust) plus the suffix -acea (relating to). Crustaceans were classified together because they all share that characteristic hard outer shell.
Crustaceans have blue blood because they use copper-based hemocyanin instead of iron-based hemoglobin like us—meaning when they bleed, the ocean literally turns blue, which is bizarre and beautiful at the same time.
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