Horseshoe crabs are ancient marine arthropods, often called “living fossils,” that are more closely related to spiders and scorpions than to true crabs. They have a distinctive hinged shell, a long tail called a telson, and unique blue blood containing a protein (LAL) used to test for bacterial contamination in medical products. These creatures are vital to the ecosystem, as their eggs are a critical food source for migratory shorebirds. #reeftank #saltwateraquarium #aquariumhobby #aquariumlife

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