American horseshoe crab

…is the single American species Limulus polyphemus, specimens of which can reach a length of more than 60 cm (2 feet), though males and females typically average lengths of 36.6–38.1 cm (14–15 inches) and 45.7–48.3 cm (18–19 inches) respectively. The other three species—the Japanese, or tri-spine, horseshoe crab (Tachypleus tridentatus),…

…on the eye of the horseshoe crab (Limulus polyphemus). Using minute electrodes in his experiments, he obtained the first record of the electrical impulses sent by a single optic nerve fibre when the receptors connected to it are stimulated by light. He found that the receptor cells in the eye…