Brief description of what you observed
Found shells of Tachypleus tridentatus, or Japanese, tri-spine horseshoe crabs on a tideland, obviously after they had molted. Tachypleus tridentatus is listed as Critically Endangered/Endangered Species on the IUCN Red List of Threatened Species.
This medium-sized Horseshoe Crab had become entangle in some fishing line on the shore of the causeway island near Sanibel, FL. We managed to untangle it and send it on it's way. Note the curled up defensive posture in one photo; it just didn't enjoy being turned upside down, even if it was necessary to get the fishing line off.
Found near shore in black mangrove forest.
Male and female pair in mating clasp.
Single cast moult recovered via dredge from RV Gemma while on an educational tour.
Found dead on the beach at Calvert Cliffs (women's size 8 sandal adjacent to specimen for perspective).
Merostomata is the name given to a grouping of the extinct Eurypterida (sea scorpions) and the Xiphosura (horseshoe crabs). The term was originally used by James Dwight Dana to refer to Xiphosura only, but was emended by Henry Woodward to cover both groups.