Xiphosura

The Xiphosura are an order of marine chelicerates that includes a large number of extinct lineages and only four extant species in the family Limulidae, which include the horseshoe crabs. The group has hardly changed in millions of years; the modern horseshoe crabs look almost identical to prehistoric genera such as the Jurassic Mesolimulus, and are considered to be living fossils. The most notable difference between ancient and modern forms is that the abdominal segments in present species are fused into a single unit in adults.

Xiphosura were traditionally placed in the class Merostomata, although this term was intended to encompass also the eurypterids, whence it denoted what is now known to be an unnatural (paraphyletic) group (although this is a grouping recovered in some recent cladistic analyses). Although the name Merostomata is still seen in textbooks, without reference to the Eurypterida, some have urged that this usage should be discouraged. The Merostomata label originally did not include Eurypterida, although they were added in as a better understanding of the extinct group evolved (see Merostomata for additional details). However, as the similarities, which were once thought to tie the group together, are now understood to be symplesiomorphies, it seems that abandoning the term altogether to avoid any confusion arising from these historical usages of the term is the best strategy.

Clearwater Marine Aquarium

The Clearwater Marine Aquarium is a 501(c)(3) non-profit organization, and aquarium in Clearwater, Florida, the hours of operation are subject to change. It is dedicated to the rescue, rehabilitation and release of sick and injured marine animals, public education, and animal-assisted therapy and research.

Clearwater Marine Aquarium opened in 1972 at its current location on Clearwater Beach, in a former water treatment plant (the large tanks being well-suited for rehabilitation operations).

Numerous forms of marine life are permanent residents at the aquarium, all of which have serious injuries that prevent their return to the wild.

The aquarium's best-known permanent resident, and the focus of its marketing campaigns, is Winter, a bottlenose dolphin who was rescued in December 2005 after having her tail caught in a crab trap. Her injuries caused the loss of her tail, and the aquarium fitted her with a prosthetic tail which brought worldwide attention to the facility. Winter later starred in the 2011 film, Dolphin Tale, and the sequel, Dolphin Tale 2, shot partially on location at the aquarium.

Atlantic horseshoe crab

The Atlantic horseshoe crab (Limulus polyphemus) is a marine chelicerate arthropod. Despite its name, it is more closely related to spiders, ticks, and scorpions than to crabs. Horseshoe crabs are most commonly found in the Gulf of Mexico and along the northern Atlantic coast of North America. A main area of annual migration is Delaware Bay, although stray individuals are occasionally found in Europe.

The other three extant species in the family Limulidae are also called horseshoe crabs. These are Tachypleus tridentatus, Tachypleus gigas and Carcinoscorpius rotundicauda, which all are restricted to Asia. All four are quite similar in form and behavior.

Names and classification

This group of animals is also known as horsefoot, or saucepan. Some people call the horseshoe crab a "helmet crab", but this common name is more frequently applied to a true crab, a malacostracan, of the species Telmessus cheiragonus. The term "king crab" is sometimes used for horseshoe crabs, but it is more usually applied to a group of decapod crustaceans.

Horseshoe crab

Horseshoe crabs are marine arthropods of the family Limulidae and order Xiphosura or Xiphosurida, that live primarily in and around shallow ocean waters on soft sandy or muddy bottoms. They occasionally come onto shore to mate. They are commonly used as bait and in fertilizer. In recent years, a decline in the population has occurred 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. Because of their origin 450 million years ago (Mya), horseshoe crabs are considered living fossils.

Classification

Horseshoe crabs resemble crustaceans, but belong to a separate subphylum, Chelicerata, and are closely related to arachnids. The earliest horseshoe crab fossils are found in strata from the late Ordovician period, roughly 450 million years ago.

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

Sea turtle

Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines. There are seven extant species of sea turtles: the green, loggerhead, Kemp's ridley, olive ridley, hawksbill, flatback, and leatherback.

Taxonomy and Evolution

Sea turtles, along with other turtles and tortoises, are part of the order Testudines. All species except the leatherback are in the family Cheloniidae. The leatherback is the only extant member of the family Dermochelyidae.

In general, sea turtles have a more fusiform body plan than their terrestrial or freshwater counterparts. The reduced volume of a fusiform body means sea turtles can not retract their head, legs, and arms into their shells, like other turtles can.

The species are primarily distinguished by their anatomy: for instance, the prefrontal scales on the head, the number of and shape of scutes on the carapace, and the type of inframarginal scutes on the plastron.

The leatherback is the only sea turtle that does not have a hard shell. Instead, it bears a mosaic of bony plates beneath its leathery skin. It is the largest sea turtle, measuring 6 to 9 feet (1.8 to 2.7 m) in length at maturity, and 3 to 5 feet (0.91 to 1.52 m) in width, weighing up to 1,500 pounds (680 kg). Other species are smaller, being mostly 2 to 4 feet (0.61 to 1.22 m) and proportionally narrower.