The Limulus Polyphemus -or horseshoe crab- is coming from the age of “visible life” that is the Paleozoic era (440 -248 million years ago).
They are older than dinosaurs, older than flowering plants, they have ten eyes, spawn on the beach, molt around 17 times in 9 to 10 years & can live up to 20 years. These days, extracts from their blood are used by the pharmaceutical industry. Their eggs — laid on the beach — are essential to migratory birds who feed on them from nests that have been disrupted by waves and storms. The feeding of shorebirds has no adverse affect on the breeding success of the horseshoe crab.
They fascinate me. Below some pix taken Saturday at Coney Island and a painting of larvae & juvenile.
For more info check this wonderful site : Limulus Polyphemus