Horseshoe crab

Horseshoe crabs are marine and brackish water arthropods of the family Limulidae, suborder Xiphosurida, and order Xiphosura.[2] Their popular name is actually a misnomer, for they are not true crabs.

Horseshoe crabs live primarily in and around shallow coastal waters on soft sandy or muddy bottoms. They tend to spawn in the intertidal zone at spring high tides.[3] They are commonly eaten in Asia, and used as fishing bait, in fertilizer and in science (especially Limulus amebocyte lysate). In recent years, population declines have occurred as a consequence of coastal habitat destruction and overharvesting.[2] Tetrodotoxin may be present in Carcinoscorpius rotundicauda.[4]

Because of their origin 450 million years ago, horseshoe crabs are considered living fossils.[5] A 2019 molecular analysis places them as the sister groupof Ricinulei within Arachnida.[6]