what class of arthropods do crabs belong to
Arthropod Arthropods belong to phylum Euarthropoda.[3][81] The phylum is sometimes called Arthropoda, but strictly this term denotes a (putative - see Tactopoda) clade that also encompasses Phylum Onychophora.[1]
Horseshoe crab Horseshoe crabs use hemocyanin to carry oxygen through their blood. Because of the copper present in hemocyanin, their blood is blue. Their blood contains amebocytes, which play a similar role to the white blood cells of vertebrates in defending the organism against pathogens. Amebocytes from the blood of L. polyphemus are used to make Limulus amebocyte lysate, which is used for the detection of bacterial endotoxins in medical applications.[19] This means there is a high demand for harvesting the blood, which involves collecting and bleeding the animals, and then releasing them back into the sea. Most of the animals survive the process; mortality is correlated with both the amount of blood extracted from an individual animal, and the stress experienced during handling and transportation.[20] Estimates of mortality rates following blood harvesting vary from 3-15%[21] to 10-30%.[22] Approximately 500,000 crabs are harvested annually.[23]