Limulidae is the only recent
familyFamily denotes a group of people or animals affiliated by a consanguinity, affinity or co-residence...
of the
orderIn scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Xiphosurida and contains all the 4 living
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
of horseshoe crabs. Horseshoe crabs fossils have been first seen in the late
DevonianThe Devonian is a geologic period and system of the Paleozoic era spanning from . It is named after Devon, England, where rocks from this period were first studied....
. Horseshoe crabs are found in shallow water on soft sandy or muddy bottoms. There has been a decline in number of individuals, as a consequence of coastal habitat destruction and pollution.
The current living species are:
- Genus Carcinoscorpius
Carcinoscorpius is a genus in the family Limulidae. It contains the following species:* Carcinoscorpius rotundicauda...
Carcinoscorpius rotundicaudaCarcinoscorpius rotundicauda is a species in the family Limulidae. It is found in India, Indonesia, Malaysia, the Philippines, Singapore, and Thailand.-Source:* World Conservation Monitoring Centre 1996. . Downloaded on 09 August 2007....
, Mangrove horseshoe crab, found in south-east Asia.
Genus Limulus
Limulus polyphemus, Atlantic Horseshoe Crab, found along the north-west Atlantic coast.
Genus TachypleusTachypleus is a genus in the family Limulidae....
Tachypleus gigasTachypleus gigas is a species in the family Limulidae. It is found in India, Indonesia, Malaysia, the Philippines, Singapore, China, and Thailand.-Source:* World Conservation Monitoring Centre 1996. . Downloaded on 10 August 2007....
, Costal horseshoe crab, found in South and South-East Asia.
Tachypleus tridentatusTachypleus tridentatus, commonly known as the Japanese horseshoe crab or the Chinese horseshoe crab, is a species in the family Limulidae. In China, horseshoe crab is known as hou . Its name in Japanese is Kabutogani , being also called hachigame, or hachigani in some localities...
, Japanese horseshoe crab, found along West Asian coasts.
The entire body of horseshoe crab is protected by a hard, dark brown carapace.
Limulidae is the only recent
familyFamily denotes a group of people or animals affiliated by a consanguinity, affinity or co-residence...
of the
orderIn scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Xiphosurida and contains all the 4 living
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
of horseshoe crabs. Horseshoe crabs fossils have been first seen in the late
DevonianThe Devonian is a geologic period and system of the Paleozoic era spanning from . It is named after Devon, England, where rocks from this period were first studied....
. Horseshoe crabs are found in shallow water on soft sandy or muddy bottoms. There has been a decline in number of individuals, as a consequence of coastal habitat destruction and pollution.
The current living species are:
- Genus Carcinoscorpius
Carcinoscorpius is a genus in the family Limulidae. It contains the following species:* Carcinoscorpius rotundicauda...
Carcinoscorpius rotundicaudaCarcinoscorpius rotundicauda is a species in the family Limulidae. It is found in India, Indonesia, Malaysia, the Philippines, Singapore, and Thailand.-Source:* World Conservation Monitoring Centre 1996. . Downloaded on 09 August 2007....
, Mangrove horseshoe crab, found in south-east Asia.
Genus Limulus
Limulus polyphemus, Atlantic Horseshoe Crab, found along the north-west Atlantic coast.
Genus TachypleusTachypleus is a genus in the family Limulidae....
Tachypleus gigasTachypleus gigas is a species in the family Limulidae. It is found in India, Indonesia, Malaysia, the Philippines, Singapore, China, and Thailand.-Source:* World Conservation Monitoring Centre 1996. . Downloaded on 10 August 2007....
, Costal horseshoe crab, found in South and South-East Asia.
Tachypleus tridentatusTachypleus tridentatus, commonly known as the Japanese horseshoe crab or the Chinese horseshoe crab, is a species in the family Limulidae. In China, horseshoe crab is known as hou . Its name in Japanese is Kabutogani , being also called hachigame, or hachigani in some localities...
, Japanese horseshoe crab, found along West Asian coasts.
Anatomy
The entire body of horseshoe crab is protected by a hard, dark brown carapace. 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. 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 molluscs, 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 60cm long (including tail).
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. The eggs take about 2 weeks to hatch. The larvae continue to molt six times during the first year.
Blood
Unlike humans, horseshoe crabs do not have haemoglobin in their blood, but instead use
hemocyaninHemocyanins are respiratory proteins in the form of metalloproteins containing two copper atoms that reversibly bind a single oxygen molecule . Oxygenation causes a color change between the colorless Cu deoxygenated form and the blue Cu oxygenated form...
to carry oxygen. Because of the copper present in hemocyanin, their blood is blue.
Their blood contains
amebocyteAn amebocyte or amoebocyte is a mobile cell in the body of invertebrates such as echinoderms, mollusks or sponges. Similar to some of the white blood cells of vertebrates, in many species amebocytes are found in the blood or body fluid and play a role in the defense of the organism against...
, which has a role similar to white blood cells for vertebrates in defending the organism against pathogens. Amebocyte from L. polyphemus is used to make
Limulus amebocyte lysateLimulus amebocyte lysate is an aqueous extract of blood cells from the horseshoe crab, Limulus polyphemus. LAL reacts with bacterial endotoxin or lipopolysaccharide , which is a membrane component of Gram negative bacteria...
, which is used for the detection of bacterial endotoxins.