7 Horseshoe Crab Characteristics: 7 Facts You Should Know!

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Horseshoe crabs are the invertebrates belonging to the subphyla- Chelicerata. Biologically, they lie in the phylum of Arthropods. Let us see some of its characteristics.

  1. Horseshoe crabs are not actual crabs because they lack antennae and mandibles.
  2. Horseshoe crabs are not death causing as they do not have venom. Only a species has a chemical substance “tetrodotoxin”, which is fatal to live beings.
  3. Horseshoe crabs possess light-sensing organs in their tails used for navigating the prey.
  4. They do have a specific type of cell-amoebocytes, which plays an important role in immune defence. That is why they are the major point of interest for scientists in biomedical purposes.
  5. They do have blue blood due to the presence of copper in hemocyanin responsible for the bright blue colour under ultraviolet light.
  6. Their tails are used for flipping so they can swim upside down.
  7. The most fascinating feature is the presence of their legs in the mouth and is used for digging.

Are horseshoe crabs endangered?

IUCN stands for International Union for Conservation of Nature and works to conserve and protect nature. Let us see if horseshoe crab are endangered or not.

Horseshoe crabs are categorised on the Red list of endangered species by IUCN in March 2019. Atlantic horseshoe crabs are grouped from vulnerable to extinction by the organization. While two other species (Tachypleus gigas, and Carcinoscorpius rotundicauda) are threatened species.

Horseshoe crab upside down
Image credits: Horseshoe crab by Adam Sofen (CC BY 2.0) from Wikimedia Commons

They are on the edge of extinction because of overexploitation by humans. As the blood of horseshoe crabs contains a coagulant- Limulus amoebocyte lysate which makes them valuable for pharmaceutical industries. But scientists are trying to explore other synthetic methods to synthesize this compound. Blood of horseshoe crabs costs for approx. 1 lakh INR.

Are horseshoe crabs omnivores?

Omnivores are organism that gets their nutrition from both herbs as well as from flesh. Let us see whether horseshoe crabs are omnivores or not.

Horseshoe crabs are omnivores. They catch their prey during the night. They mostly feed upon soft shell molluscs, razor clams, some marine larvae and algae. As they do not have jaws and teeth, abdominal legs play a vital role in crushing and grinding.

Some horseshoe crabs are also detrivores. Example: Carcinoscorpius rotundicauda. They eat other organisms to obtain enough energy which can be used for their bodily functions.

Are horseshoe crabs arachnids?

Arachnida is one of the major classes of Arthropoda. Some members also have venom and can sting to affect humans. Let us see whether horseshoe crab belongs to arachnids or not.

Horseshoe crabs are arachnids because they possess some salient features like non-working 1 or 2 appendages. The head and thorax fuse to form the cephalothorax, with no antennae or wings. That is why they are not real crustaceans or crabs.

The body is covered with a hard covering known as carapace ranging from the cephalothoracic region and reduced appendages are known as Chilaria. Some members have a whip-like tail or telson which may contain an unfavourable substance.

Are horseshoe crabs blind?

The eyes are the organs which can respond to light in both vertebrates and invertebrates. Let us see whether horseshoe crabs are blind or not.

Horseshoe crabs are not blind. As they do have nine eyes i.e., 7 simple and 2 compound eyes composed of ommatids act as lenses which give monochromatic vision to these organisms. These eyes from the mosaic-like structure of the object and image are not so clear, fine and colourful.

As eyes are the light-sensing organ in many organisms but in a few, other organs have receptors to light like in horseshoe crabs, tails have a series of receptors which can respond to visible light.

Are horseshoe crab invertebrate?

Invertebrates are those who do not have a vertebral column at any stage of their life. These are known as lower chordates. Let us see if horseshoe crabs are invertebrates or not.

Horseshoe crabs are invertebrates that belong to the phylum Arthropoda. From Porifera to echinoderms, all are invertebrates as they are devoid of the vertebral column. They only have a chitinous exoskeleton that provides rigidity and aids in support and movement.

Are horseshoe crabs intelligent?

Intelligence is a feature of vertebrates mostly mammals as it depends upon the cranial capacity. Let us see if horseshoe crabs are intelligent or not.

Horseshoe crabs are not as intelligent as humans. They are sensitive, and conscious and show some reactions against stimuli due to developing but incomplete nervous systems. But they do not have brains like human.

Are horseshoe crabs mammals?

Mammals are the higher animals in the hierarchy of animal kingdom classification. They have all the characteristic features of vertebrates.

Horseshoe crabs are not mammals as they do not have any features regarding the class. They do not have vertebral columns and notochord. They are oviparous and have an incomplete organ system. They do not have sensory organs like ear, tongue etc. and are ammonotelic.   

They lack teeth, jaws and focused visual organs. They show in vitro fertilization and lay eggs. They do not have a closed circulatory system and RBCs in their blood.

Conclusion

In my conclusion, horseshoe crabs have interesting features. But due to anthropogenic activities, it became vulnerable and may lead to extinction soon.

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