Horseshoe crab

From Wikivisual

Horseshoe crabs are arthropods that live primarily in shallow ocean waters on soft sandy or muddy bottoms. They will, however, occasionally come on shore, e.g. for mating. They are commonly used as bait and in fertilizer, and in recent years there has been a decline in number of individuals, as a consequence of coastal habitat destruction in Japan and overharvesting along the east coast of North America. Tetrodotoxin may be present in the roe of species inhabiting the waters of Thailand.<ref>Kungsuwan, Attaya; Yuji Nagashima, Tamao Noguchi (1987). "Tetrodoxin in the Horseshoe Crab Carcinoscorpius Rotundicauda Inhabiting Thailand". Nippon Suisan Gakkaishi 53: 261-266. http://rms1.agsearch.agropedia.affrc.go.jp/contents/JASI/pdf/society/34-3054.pdf. Retrieved 6 January 2011. 

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Contents 1 Classification 2 Anatomy 3 Breeding 4 Blood 5 Horseshoe crabs and Mankind 5.1 Consumption 5.2 Fishing 5.3 In culture 6 References 7 External links

[edit] Classification

Horseshoe crabs look similar to crustaceans, but actually belong to Chelicerata, and are therefore more closely related to spiders and scorpions. The earliest horseshoe crab fossils are found in geologic layers from the late Ordovician period, roughly 450 million years ago. Unlike most species which go extinct after approximately 10 million years on average, the horseshoe crab has changed remarkably little in the last 250 million years.

Limulidae is the only recent family of the order Xiphosurida and contains all the 4 living species of horseshoe crabs:

• Genus Carcinoscorpius
  • Carcinoscorpius rotundicauda, mangrove horseshoe crab, found in Southeast Asia.
• Genus Limulus
  • Limulus polyphemus, Atlantic horseshoe crab, found along the northwest Atlantic coast and in the Gulf of Mexico.
• Genus Tachypleus
  • Tachypleus gigas, coastal horseshoe crab, found in South and Southeast Asia.
  • Tachypleus tridentatus, Japanese horseshoe crab, found along East Asian coasts.

[edit] Anatomy

The entire body of the horseshoe crab is protected by a hard shell. They have two large compound eyes and multiple smaller simple ones atop the carapace. Beneath the carapace they look quite similar to a large spider. They have five pairs of legs for walking, swimming and moving food into the mouth. The long, straight, rigid tails can be used to flip themselves over if they are turned upside down, so a crab with a broken tail may die.

Behind their legs, they have book gills, which exchange respiratory gases and are also occasionally used for swimming. While they can swim upside down, they usually are found on the ocean floor searching for worms and mollusks, which are their main food. They may also feed on crustaceans and even small fish.

Females are larger than males, C. rotundicauda is the size of a human hand, while L. polyphemus can be up to 60 centimetres (24 in) long (including tail). The juveniles grow about 33% larger with every molt until reaching adult size.<ref>Cartwright-Taylor, Lesley; Julian Lee, Chia Chi Hsu (2009). "Population structure and breeding pattern of the mangrove horseshoe crab Carcinoscorpius rotundicauda in Singapore". Aquatic Biology 8: 61–69. doi:10.3354/ab00206. http://www.int-res.com/abstracts/ab/v8/n1/p61-69/. </ref>

[edit] Breeding

During the breeding season, horseshoe crabs migrate to shallow coastal waters. Males select a female and cling onto her back. The female digs a hole in the sand and lays her eggs while the male fertilizes them. The female can lay between 60,000–120,000 eggs in batches of a few thousand at a time. Many shore birds eat the eggs before they hatch. The eggs take about 2 weeks to hatch. The larvae molt six times during the first year.

[edit] Blood

Unlike humans, horseshoe crabs do not have hemoglobin in their blood, but instead use hemocyanin to carry oxygen. Because of the copper present in hemocyanin, their blood is blue. Their blood contains amebocytes, which play a role similar to white blood cells for vertebrates in defending the organism against pathogens. Amebocytes from the blood of L. polyphemus are used to make Limulus amebocyte lysate, which is used for the detection of bacterial endotoxins.

[edit] Horseshoe crabs and Mankind

[edit] Consumption

Horseshoe crabs is the lovers' crab in Vietnam because the male strongly clings to the female ; lovers must eat them both together.

[edit] Fishing

Horseshoe crab are used as bait to fish for eels (mostly in the USA). However, fishing horseshoe crab is temporarily forbidden in New Jersey and Delaware (moratorium on harvesting), where their population has become too small. This low population also endangers the future of the red knot. They are protected birds and feed on protein-rich horseshoe crab eggs during their stopover on New Jersey and Delaware's beaches.<ref>http://www.ens-newswire.com/ens/mar2008/2008-03-26-093.html</ref>

[edit] In culture

The Horseshoe crab inspired Hans Ruedi Giger's alien while in its Facehugger state. It also inspired Nintendo Pokemon Kabuto. In Japanese, the horseshoe crab is "Kabuto-gani" : it is named after the Samurai's helmet (Kabuto).

[edit] References

[edit] External links

• Horseshoe Crab History, Biology, Research and Conservation
• Science Friday Video: Horseshoe Crab Season
• Horseshoe crab at the Smithsonian Ocean Portalda:Dolkhale

de:Pfeilschwanzkrebse es:Xiphosura fa:خرچنگ نعلی fr:Limulidae id:Belangkas it:Limulidae ja:カブトガニ綱 nl:Degenkrabben pl:Skrzypłocz ru:Мечехвосты sk:Hrotnáčovité th:แมงดาทะเล vi:Họ Sam zh:鱟