Cephalothorax

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Cephalothorax

The cephalothorax (called the prosoma in some groups) is an anatomical

Anatomy

Anatomy is a branch of biology that is the consideration of the body plan. It is a general term that includes human anatomy, animal anatomy and plant anatomy ....
term used in arachnids and malacostraca

Malacostraca

The Malacostraca are the largest class of crustaceans and include most of the animals that non-experts recognize as crustaceans, including Decapoda , stomatopods and euphausiids ....
n crustaceans for the first (anterior) major body section. The remainder of the body is the abdomen

Abdomen

In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity....
(opisthosoma), which may also bear lateral appendages as well as the tail

Tail

The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals and birds....
, if present. The term "prosoma" can also be applied to the head of insects, but as the two are always exactly synonymous in insects (not true for mesosoma

Mesosoma

The mesosoma is the middle part of the body, or tagma , of arthropods whose body is composed of three parts, the other two being the prosoma and the metasoma....
vs. thorax

Thorax

The thorax is a division of an animal's body that lies between the head and the abdomen.In mammals, the thorax is the region of the body formed by the sternum, the thoracic vertebrae and the ribs....
or metasoma

Metasoma

The metasoma is the posterior part of the body, or tagma , of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma....
vs. abdomen

Abdomen

In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity....
), the simpler term - "head" - is used instead.

he chelicerates

Chelicerata

The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda, and includes horseshoe crabs, scorpions, spiders and mites....
, the cephalothorax does not originate from any fusion of head and thorax, because there is no post-cephalic tagmosis

Tagmosis

Tagmosis is the evolutionary process of wiktionary:fuse and modifying segments in metamerism organisms such as arthropods to form tagma ta. In insects, the body segments have become fused into three main tagmata: the head, thorax and abdomen....
(no thorax) in their immediate ancestors.

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Encyclopedia

The cephalothorax (called the prosoma in some groups) is an anatomical

Anatomy

Malacostraca

Abdomen

Tail

Mesosoma

The mesosoma is the middle part of the body, or tagma , of arthropods whose body is composed of three parts, the other two being the prosoma and the metasoma....
vs. thorax

Thorax

Metasoma

The metasoma is the posterior part of the body, or tagma , of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma....
vs. abdomen

Abdomen

Chelicerate cephalothorax

In the chelicerates

Chelicerata

Tagmosis

Chelicerata

The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda, and includes horseshoe crabs, scorpions, spiders and mites....
is formed by the fusion of the head segments and some anterior trunk segments. Recommended usage is prosoma versus opisthosoma

Opisthosoma

The opisthosoma is the posterior portion of the arachnids body behind the prosoma . The number of segments and appendages on the opisthosoma vary....
. The dorsal sclerites of the cephalothorax are typically fused into a shield called a carapace

Carapace

A carapace is a Dorsum section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids as well as vertebrates such as chelonians, order Testudines, turtles and tortoises....
, while the ventral ones are much reduced and usually covered by the coxae of pedipalps and legs I-IV.

Horseshoe crabs are quite unusual in that part of the first two opisthosomal segments have actually become incorporated into their prosoma, and here the term cephalothorax has been proposed as a specific name for this modified anterior part of the horseshoe crab body.

Crustacean cephalothorax

The crustacean cephalothorax is derived from the fusion of the head (from Greek

Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
cephale) and the trunk (from Greek thorax), and therefore includes all the mouthparts, antennae

Antenna (biology)

Antennae are paired appendages connected to the front-most morphogenesis of arthropods. In crustaceans, they are biramous and present on the first two segments of the head, with the smaller pair known as antennules....
, and the thoracic appendage

Appendage

An appendage in the broadest sense is an additional or subsidiary part existing on, or added to, something which can generally still function if the appendage has never existed or is later provided or grown, or will still perform a primary function if the appendage is removed....
s, such as the legs of a lobster

Lobster

Clawed lobsters compose a family of large marine crustaceans. Lobsters are economically important as seafood, forming the basis of a global industry that nets United States dollar1.8 billion in trade annually....
. In the Malacostraca, the cephalothorax is typically covered by a protective carapace

Carapace