Horseshoe crab

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Relevance: The Hindu

Horseshoe crabs are arthropods of the family Limulidae and the only surviving xiphosurans. Despite their name, they are not true crabs or even crustaceans; they are chelicerates, more closely related to arachnids like spiders, ticks, and scorpions. The body of a horseshoe crab is divided into three main parts: the cephalothorax, abdomen, and telson. The largest of these, the cephalothorax, houses most of the animal's eyes, limbs, and internal organs. It is also where the animal gets its name, as its shape somewhat resembles that of a horseshoe. Horseshoe crabs have been described as "living fossils", having changed little since they first appeared in the Triassic.

Only four species of horseshoe crab are extant today. Most are marine, though the mangrove horseshoe crab is often found in brackish water. Additionally, certain extinct species transitioned to living in freshwater. Horseshoe crabs primarily live at the water's bottom but they can swim if needed. In the modern day, their distribution is limited, only found along the east coasts of North America and South Asia.

Horseshoe crabs are often caught for their blood, which contains Limulus amebocyte lysate, a chemical used to detect bacterial endotoxins. Additionally, the animals are used as fishing bait in the United States and eaten as a delicacy in some parts of Asia. In recent years, horseshoe crabs have experienced a population decline. This is mainly due to coastal habitat destruction and overharvesting. To ensure their continued existence, many areas have enacted regulations on harvesting and established captive breeding programs.

The Limulidae are the only recent family of the order Xiphosura, and contain all four living species of horseshoe crabs: 

1. Carcinoscorpius rotundicauda, the mangrove horseshoe crab, found in Southeast Asia. 

2. Limulus polyphemus, the Atlantic horseshoe crab, found along the American Atlantic coast and in the Gulf of Mexico. 

3. Tachypleus gigas, found in Southeast and East Asia. 

4. Tachypleus tridentatus, found in Southeast and East Asia. 

Tachypleus gigas and Carcinoscorpius rotundicauda are found within Indian limits. The distribution of T. gigas and C. rotundicauda is restricted to north-east coast of Orissa and Sunderbans area of the West Bengal, respectively. 

Few people realize how important horseshoe crabs are to modern medicine. Because their blue, copper-based blood quickly clots in the presence of bacterial toxins, medical researchers use it to test intravenous drugs, vaccines, and medical devices, ensuring that they are free of bacterial contamination. 

  1. National Oceanic and Atmospheric Administration (NOAA)
  2. Horseshoe crab
  3. Tachypleus gigas
  4. Mangrove horseshoe crab
  5. Bihar Animal Sciences University


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