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Horseshoe
Crab - any of four species of marine arthropods of the order
Xiphosura (class Merostomata), found on the east coasts of Asia and North
America. Despite their names, these animals are not crabs
at all but rather are related to the scorpions, spiders, and extinct
trilobites.
Horseshoe
crabs are of extremely ancient
origin and are often referred to as living fossils. Their fossil relatives
are recognized as far back as the Ordovician Period (505 to 438 million
years ago), and forms similar to modern-day horseshoe
crabs date back to the Jurassic
Period (208 to 144 million years ago). The present genera include two
along the coast of Asia and one along North America. Best known is the
single American species Limulus polyphemus, specimens of
which can reach a length of more than 2 feet. The animals are most
abundant in estuarine waters, in winter at moderate depths and in summer
often on intertidal mud flats. Horseshoe
crabs have been used as food by
humans and are a serious enemy of the soft-shelled crab.
"horseshoe
crab." Encyclopędia
Britannica from Encyclopędia Britannica Premium Service. |
