Limulus polyhemus, the Atlantic horseshoe crab. Little changed in 300 million years, which means they watched the dinosaurs go. They are mating this month, the larger females coming up with the high tide, the smaller males (sometimes several of them) attached to their backs, to lay their eggs at the high water line. More related to the spiders than the crustaceans, these familiar creatures need all the resilience they’ve mastered over the years. They are chopped up for chum for the eel and conch fisheries by the millions. They are besieged by habitat destruction and pollution and global climate change. A keystone species, their diminishing numbers mean that many shore birds, particularly the red knot, are doing poorly, since migrating birds depend on the protein orgy provided by horseshoe crab eggs.
A primitive lifeform, a living fossil? Perhaps, but some of you would not be alive without them today. A compound extracted from their blood is used by pharmaceutical and medical device manufacturers to test for bacterial contamination. Bacteria endotoxins can't be sterilized away, so it’s actually federal law that vaccines, IV drugs, and medical devices have to be tested with limulus amebocyte lysate, or LAL. You can read more about this little-known but fascinating subject here.
(The image above is not a fossil, it's a design pressed into the concrete at the Lenape Playground in Marine Park.)