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| Merostomata
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Merostomata is a class of marine arthropods which includes horseshoe crabs and eurypterids. It includes only four living species.
Xiphosura contains the four living species of the class. The best known species is the horseshoe crab (Limulus polyphemus), whose ancestors can first be seen in the Devonian period's fossil record. They are found along the northwestern Atlantic coast and in the Gulf of Mexico. Horseshoe crabs are found in shallow water on soft sandy bottoms.
The entire body of horseshoe crab is protected by a hard, dark brown carapace. They have two large compound eyes and three smaller simple ones atop the carapace. Beneath the carapace they look quite similar to a large spiderSuborder Mesothelae Liphistiidae (primitive burrowing spiders) Suborder Mygalomorphae Atypidae ( atypical tarantula) Antrodiaetidae ( folding trapdoor spider) Mecicobothriidae ( dwarf tarantulas) Hexathelidae ( venomous funnel-web tarantula) Dipluridae (. They have six pairs of legs for walking, swimming and moving food into the mouth. Behind their legs, they have six book gills, which exchange respiratory gases and are also used for swimming. While they can swim upside down, they usually are found on the ocean floor searching for worms and molluskCaudofoveata Aplacophora Polyplacophora Chitons Monoplacophora Bivalvia Bivalves Scaphopoda Tusk shells Gastropoda Snails and Slugs Cephalopoda Squids, Octopuses, etc. The mollusks or molluscs are the large and diverse phylum Mollusca which includes a vars, which are their main food. They may also feed on crustaceanCrustaceans Hyalella azteca Scientific classification Kingdom: Animalia Phylum: Arthropoda Subphylum Crustacea Classes Remipedia Cephalocarida Branchiopoda Ostracoda Maxillopoda Malacostraca The crustaceans (Crustacea) are a large group of arthropods (55,s and even small fishAtlantic herring, Clupea harengus one of the most abundant species in the world Photo A fish is a poikilothermic (cold-blooded) water-dwelling vertebrate with gills. There are over 27,000 species of fish, making them the most diverse group of vertebrates..
In the spring, Horseshoe crabs migrate to certain shallow coastal waters. Males select a female and cling onto her back. They use holes in sand to lay eggs. These holes are 10-25cm in height. The female usually lays up 1,000 eggs in this hole and the male releases his sperm onto them so that they can be fertilised. These larvae take about 16 weeks to hatch, and it takes another 6 months to reach adult stage. They can reach sexual maturity in 3 years or more.
The young stay here, light brown in color at first, and migrate into deeper waters as they get older. They used to be harvested for fertilizer, but their only current commercial value is that they are sometimes chopped up for lobster bait.
The other three species of this subclass are found along Asian coasts from Japan and Korea, down to the Philippines.