Loren, a biology graduate student, writes, “It’s a sketch of the horseshoe crab Limulus, such as a zoologist would make (and with the abdominal segments correctly identified). Perhaps the most magnificent living fossil of all, the horseshoe crab is the survivor of a lineage that extends back some 445 million years into the Ordovician. The four extant species are the only living representatives of the ancient arthropod class Merostomata and the only known chelicerate crabs.”