Horseshoe crab

Horseshoe crabs are <a href="/facts/Arthropod/JKJLTFzp">arthropods</a> of the family Limulidae and the only surviving <a href="/facts/Xiphosura/C2JVjLpj">xiphosurans</a>. Despite their name, they are not true <a href="/facts/Crab/GvkhXnSK">crabs</a> or even <a href="/facts/Crustaceans/PBobIVJP">crustaceans</a>; they are <a href="/facts/Chelicerata/9YNa15kz">chelicerates</a>, more closely related to <a href="/facts/Arachnid/xPJbsLga">arachnids</a> like <a href="/facts/Spider/aqpU7eg3">spiders</a>, <a href="/facts/Tick/LNe33WJf">ticks</a>, and <a href="/facts/Scorpion/clJKHDdY">scorpions</a>. The body of a horseshoe crab is divided into three main parts: the <a href="/facts/Cephalothorax/0CER7JDU">cephalothorax</a>, <a href="/facts/Opisthosoma/rXmmsVrX">abdomen</a>, and <a href="/facts/Telson/71eFnSJb">telson</a>. The largest of these, the cephalothorax, houses most of the animal's <a href="/facts/Eye/h3lbYU55">eyes</a>, limbs, and <a href="/facts/Internal_organs_of_arthropods/JKJLTFzp">internal organs</a>. It is also where the animal gets its name, as its shape somewhat resembles that of a <a href="/facts/Horseshoe/5gXPTqFB">horseshoe</a>. Horseshoe crabs have been described as "<a href="/facts/Living_fossil/EujFvU2D">living fossils</a>", having changed little since they first appeared in the <a href="/facts/Triassic/r6CNxKXC">Triassic</a>.
Only four species of horseshoe crab are extant today. Most are <a href="/facts/Marine_life/TF5MGzFb">marine</a>, though the <a href="/facts/Mangrove_horseshoe_crab/XwycKvzE">mangrove horseshoe crab</a> is often found in <a href="/facts/Brackish_water/f6z3UXCa">brackish water</a>, and the <a href="/facts/Atlantic_horseshoe_crab/lJlYkhfC">Atlantic horseshoe crab</a> is resident in brackish estuarine ecosystems such as the <a href="/facts/Delaware_Bay/mbQIQruo">Delaware</a> and <a href="/facts/Chesapeake_Bay/IBeolBQc">Chesapeake</a> bays. Additionally, certain extinct species transitioned to living solely in <a href="/facts/Fresh_water/xMP2TxwI">freshwater</a>. Horseshoe crabs primarily live at the <a href="/facts/Benthic_zone/N3lM6P7I">water's bottom</a> but they can swim if needed. In the modern day, their distribution is limited, only found along the coasts of the western <a href="/facts/Atlantic_Ocean/EI4uChIb">Atlantic Ocean</a> in <a href="/facts/North_America/djNjCQIl">North America</a>, and the <a href="/facts/Central_Indo-Pacific/jmkcFlh2">Central Indo-Pacific</a> in <a href="/facts/South_Asia/7gTqe3hY">South</a> and <a href="/facts/Southeast_Asia/VafwT517">Southeast Asia</a>.
Horseshoe crabs are often caught for their <a href="/facts/Blood/03zEulkj">blood</a>, which contains <a href="/facts/Limulus_amebocyte_lysate/M5BmAkYR">Limulus amebocyte lysate</a>, a chemical used to detect bacterial <a href="/facts/Endotoxin/Ch967TXw">endotoxins</a>. Additionally, the animals are used as fishing bait in the <a href="/facts/United_States/P0sCdLe5">United States</a> and eaten as a delicacy in some parts of <a href="/facts/Asia/4IToYrrQ">Asia</a>. In recent years, horseshoe crabs have experienced a population decline. This is mainly due to coastal <a href="/facts/Habitat_destruction/pyPMkBCY">habitat destruction</a> and overharvesting. To ensure their continued existence, many areas have enacted regulations on harvesting and established captive breeding programs.

Horseshoe crab open-in-new

Horseshoe crab