Limulus polyphemus, the Atlantic horseshoe crab, is a marine arthropod considered a “living fossil” extending back approximately 450 million years. The blood color is blue due to the presence of hemocyanin and contains amoebocytes, used to detect toxins. Its genome presents specific duplications of  genes related to innate immunity. https://doi.org/10.1186/2047-217X-3-9, 05/14/2014 Author: Guillem Dachs Margarit