User:RenaMoonn/sandbox

Updated the synopsis so that it does not include links to information used later in the article. This was done to match the format of the Crocodilia, Aves, Bacteria, Archaea, and Evolution articles. Removed the fossil Limulid pictures from the taxabox to make the article more aesthetically pleasing. Additionally removed the genera list and placed it in the taxabox for the same reason (as well as for saving space). Expanded the culinary use section and moved irrelevant overharvesting information to the conservation section. Somewhat simplified the morphological stasis section, but the first paragraph needs a source.

Horseshoe crabs are marine and brackish water arthropods of the family Limulidae and are the only surviving Xiphosurans. Despite their name, they are not true crabs or crustaceans. Rather, they are chelicerates. This makes them more closely related to arachnids like spiders, ticks, and scorpions.

The body of a horseshoe crab is divided into three main parts: the cephalothorax, abdomen, and telson. The largest of these, the cephalothorax, houses the majority of the animal's eyes, limbs, and internal organs. It's also where the animal gets its name, as its shape somewhat resembles that of a horseshoe.

Horseshoe crabs primarily live on the bottom of shallow coastal waters, but can swim if needed. These animals are occasionally used as fishing bait, but they are also eaten in some parts of Asia. More commonly, horseshoe crabs are caught for their blood, something valuable to the medical industry. This use comes from the Limulus amebocyte lysate, a chemical in their blood for the detection of bacterial endotoxins.

In recent years, these animals have experienced a population decline. This is mainly due to coastal habitat destruction and overharvesting.

Phylogeny and Evolution
The fossil record of Xiphosurans extends all back to the Ordovician, or around 445 million years ago. For modern horseshoe crabs, their earliest appearance was approximately 250 million years ago during the Early Triassic. As their bodies have barely changed between then and the present, extant forms have been described as "living fossils".

Horseshoe crabs resemble crustaceans but belong to a separate subphylum of the arthropods, Chelicerata. Horseshoe crabs are closely related to the extinct eurypterids (sea scorpions), which include some of the largest arthropods to have ever existed, and the two may be sister groups. The enigmatic Chasmataspidids are also thought to be closely related to the horseshoe crabs.

The radiation of horseshoe crabs occurred rapidly and resulted in 88 known lineages, of which only 4 remain. The Atlantic species is sister to the three Asian species, the latter of which are likely the result of two divergences relatively close in time. The last common ancestor of the four extant species is estimated to have lived about 135 million years ago in the Cretaceous.

The Limulidae are the only extant family of the order Xiphosura, and contains all four living species of horseshoe crabs:


 * Carcinoscorpius rotundicauda, the mangrove horseshoe crab, found in South and Southeast Asia
 * Limulus polyphemus, the Atlantic or American horseshoe crab, found along the Atlantic coast of the United States and the Southeast Gulf of Mexico
 * Tachypleus gigas, the Indo-Pacific, Indonesian, Indian or southern horseshoe crab, found in South and Southeast Asia
 * Tachypleus tridentatus, the Chinese, Japanese or tri-spine horseshoe crab, found in Southeast and East Asia

Adaptation to Freshwater
According a phylogeny from 2015, now-extinct xiphosurans traveled to freshwater at least five times throughout history. This same transition happened twice in the horseshoe crabs Victalimulus and Limulitella, with both inhabiting marginally marine environments such as swamps and rivers. In contrast, all extant species are predominantly marine.

Morphological Stasis
As generalists, horseshoe crabs have a broad diet and can live in diverse habitats, meaning they are more likely to survive and produce viable offspring in new places. Horseshoe crabs also have an incredibly efficient immune system, and can also be successful in areas with high concentrations of bacteria. This is accomplished through immune cells known amoebocytes which live in the animal's bloodstream. When they attack, amoebocytes envelop their target, acting like a coagulant and preventing foreign bodies from multiplying. This trait is an adaptation to their often bacteria-rich environment. Horseshoe crab's ability to succeed in many environments limits selective forces, as there are few, if any, mutations that would make them more suited for survival.

Diet
Horseshoe crabs are more often 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. Foraging usually takes place at night. Gravel and sand particles are ingested to further grind up food in a gizzard before passing it into the stomach.

Growth and Development
Females are about 20–30% larger than males. The smallest species is C. rotundicauda and the largest is T. tridentatus. On average, males of C. rotundicauda are about 30 cm long, including a tail (telson) that is about 15 cm, and their carapace (prosoma) is about 15 cm wide. Some southern populations (in the Yucatán Peninsula) of L. polyphemus are somewhat smaller, but otherwise this species is larger.

In the largest species, T. tridentatus, females can reach as much as 79.5 cm long, including their tail, and up to 4 kg in weight. This is only about 10-20 cm longer than the largest females of L. polyphemus and T. gigas, but roughly twice the weight.

The juveniles grow about 33% larger with every molt until reaching adult size. Atlantic horseshoe crabs molt in late July.

Reproduction
During the breeding season (spring and summer in the Northeast U.S.; year-round in warmer locations or when the full moon rises), horseshoe crabs migrate to shallow coastal waters. There they spawn on beaches and salt marshes. The smaller male horseshoe crab clings to the back or opisthosoma of the larger female using specialized front claws and fertilizes the eggs as they are laid in the sand. Additional males called "satellite males" which are not attached to the female may surround the pair and have some success in fertilizing eggs. Young female horseshoe crabs can be identified by the lack of mating scars.

The female can lay between 60,000 and 120,000 eggs in batches of a few thousand at a time. The eggs may be inseminated within 20 to 30 minutes. In L. polyphemus, the eggs take about two weeks to hatch; shore birds eat many of them before they hatch. The larvae molt six times during the first year and annually after the first 3 or 4 years.

Natural breeding of horseshoe crabs in captivity has proven to be difficult. Some evidence indicates that mating takes place only in the presence of the sand or mud in which the horseshoe crab's eggs were hatched; it is not known with certainty what is in the sand that the crabs can sense or how they sense it. Artificial insemination and induced spawning have been done on a relatively large scale in captivity, and eggs and juveniles collected from the wild are often raised to adulthood in captivity.

In order to preserve and ensure continuous supply of horseshoe crabs, a breeding center was built in Johor, Malaysia where the crabs are bred and released back into the ocean in the thousands once every two years. It is estimated to take around 12 years before these animals are suitable for consumption.

Consumption
While not having much meat, horseshoe crabs are valued as a delicacy in many parts of East and Southeast Asia. The meat is white, has a rubbery texture similar to lobster, and possesses a slightly salty aftertaste. Horseshoe crab can be eaten both raw and cooked, but must be properly handled to prevent food poisoning.

Horseshoe crab is commonly prepared by grilling or stewing, but the meat can also be pickled in vinegar or stir-fried with veggies. Many recipes involve the use of various spices, herbs, and chilies to give the dish more flavor.

In addition to the meat, horseshoe crabs are also valued for their eggs.

The eggs are eaten in parts of Southeast Asia, Johor and China.

Use in Fisheries
Horseshoe crabs are used as bait to fish for eels (mostly in the United States), whelk, or conch. Nearly 1 million (1,000,000) crabs a year are harvested for bait in the United States, dwarfing the biomedical mortality. However, fishing with horseshoe crab was banned indefinitely in New Jersey in 2008 with a moratorium on harvesting to protect the red knot, a shorebird which eats the crab's eggs. A moratorium was restricted to male crabs in Delaware, and a permanent moratorium is in effect in South Carolina.

A low horseshoe crab population in the Delaware Bay is hypothesized to endanger the future of the red knot. Red knots, long-distance migratory shorebirds, feed on the protein-rich eggs during their stopovers on the beaches of New Jersey and Delaware. An effort is ongoing to develop adaptive-management plans to regulate horseshoe crab harvests in the bay in a way that protects migrating shorebirds.