“Horseshoe crab blood is bright blue. … Scientists used [the crabs’] clever blood cells to develop a test … which checks new vaccines for contamination.” —Natural History Museum, Londonupturned on the lab bench like a melon, halved: we drew the undulating outline of a horseshoe crab, then sketched the legs tucked in like seeds, studied the way her body shelled itself. grasping legs / walking legs / pushing legs. book gills, like ribs, filled in her abdomen. we traced the arc of carapace, the compound eyes embedded in prosoma, the hinge and spines. meanwhile, on Atlantic beaches, horseshoe crabs swam up to swarming shores, tripped over their own arachnid spawning: shells pressed close to shells, gills held by the shallow swell of waves against the sand. the water balmy, dense with moonlit mating. and meanwhile, too, horseshoe crabs spilled their blue blood into glass jars while strapped to the factory line, their seedlike legs turned inward, bodies tapped for miracle coagulants. our miracle / their wane. each vial brimmed with the drained- blood promise of safety, blue like the bay where the crabs were sent back, once bled, to see if they could still cling to the salt.