Modern forms






 Limulus polyphemus

 Eastern America

 Largest Living Species

 Carcinoscorpius rotundicauda


 Smallest Living Species

 Tachypleus gigas

 South East Asia

 Tachypleus tridentatus

 South East Asia


Limulus polyphemus:


Out of the four remaining species, Limulus polyphemus is the largest and best known. Its geographical distribution ranges between approximately 19° North to 42° North along the east coast of North America. Ranging from Maine in the far north to the Yucatan peninsula in Mexico, L. polyphemus populations show a distinct latitudinal gradient, exhibiting discrete genetic variation. The peak abundance occurs in Delaware Bay, New Jersey, USA.
L. polyphemus are ecologically very important, its eggs provide food for threatened loggerhead sea turtles, alligators, wading birds and many fish species. Its foraging technique aerates substrata thereby affecting infaunal communities. However there has been an alarming decline in population numbers over the last twenty years, threatening a diverse ecosystem. The decline has been caused by the high commercial value placed on the organism. The horseshoe crab has extensive pharmaceutical and biomedical application. Compounds within its respiratory pigment are a vital component in the manufacture of intravenous solutions, antibiotics, and kidney dialysers. Currently there are no legal protections for this species and no controls on horseshoe crab "harvesting" thus potentially threatening the future of the species and an ecosystem.


(Photo by Peter Dyrynda 2003-04. Used with permission according to the copyright terms and conditions)

Carcinoscorpius rotundicauda:


C. rotundicauda which is also known as the "mangrove horseshoe crab" is an Indian species and the smallest extant xiphosuran. Horseshoe crabs are generally considered to be entirely marine though C. rotundicauda has been recorded entering rivers in India and was once caught 145 km (96 miles) upstream. This highlights its ability to adapt to fluctuating conditions (salinity). Cladistic analysis placed it closer to the tribe Tachypleus than L. polyphemus. It is considered to be the sister taxon to the clade which includes T. gigas and T. tridentatus, with L. polyphemus most distantly related. As with L. polyphemus, its biomolecular properties are used in the biomedical industry. Haemagglutinin is extracted from the amoebocytes of the crab, which is used an an arteficial blood clotting agent.


Tachypleus gigas:


T. gigas which is also known as the " coastal or Singapore horseshoe crab" occurs around the coast of South Asia. It is distinguished from its sister taxon T. tridentatus by its size, colour, shape of the tail and the number of spines at the base of the opisthosoma. Its ecology and serology are almost identical. Populations have been severely reduced due to habitat destruction and pollution, threatening the future of this species.


Tachypleus tridentatus:


T. tridentatus is also known as the "Chinese horseshoe crab" and is the sister taxon to T. gigas. It is smaller in size and has a serated telson. Its ecology and serology are almost identical to T. gigas making it a valuble source to the biomedical industry.

Author: Andrew Przewieslik
Last updated: 21/11/05
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Websites produced by students on the MSc Palaeobiology programme in the Department of Earth Sciences at the University of Bristol for academic year 2005-6