Carapace

Carapace (from gr charax " fortification ", " Palisade " and pagios "fixed"; plural: Carapaces ) is a term for a different animal groups ( taxa ) resulting independently hard cover the body top.

Crustaceans

Many crustaceans (Crustacea ) have a fold of skin from the head trailing edge ( segment of the second maxilla ) emanates; this can also be primary ( eg Cephalocarida ) or secondary (eg isopods and amphipods ) are missing, so not part of the basic blueprint of crustaceans. In many cases, the chitinous head fold is by intercalated limestone armor- reinforced, especially in many decapods. Clear this structure as carapace some or possibly all body segments, it is called the carapace.

So the carapace close to the head on, continues on its rear edge, and still extends more or less over the body of the cancer. Depending on the design it can also envelop the head itself (eg for the ostracods ) and his far also pulled down more or less sideways. The carapace is a Hautduplikatur of the cuticular exoskeleton, that is, it is double-layered and inside of tissues met ( at least a double-layered epidermis with their utilities ). The underlying hull has additionally its own cuticle. In the decapods ( Decapoda ), such as crab, shrimp and lobster -like, the back part of the carapace is called Notum, the lateral parts are called pleura ( the same name, but not homologous to the so- called side plates of insects). The carapace is generally unrelated to the structures of the original body segmentation (which he covered ).

The degree of hull coverage is pronounced differently in the various cancer groups. The ostracods and claws tails (water fleas, including the mussel bivalves ) the Company's most goes here enveloped the carapace the entire body a. This extreme form consists of two shells, a complete cleavage of the shells is carried on each side of the body, he is so zweiklappig like a conch shell, because along the center line on the back ( dorsal). The claws tails the shells merge into each other, so this configuration is referred to as two-lobed. In the so-called higher crayfish he is merged with a different number of segment tops ( tergites ) and forms with them a rigid unit. There are also cancer groups in which the carapace is fused at any point with the covered segments, such as in the "Primeval cancer " Triops. The tank is here connected to the body only at the top rear edge and is loosely based on the fuselage. The carapace may forward into an unpaired, in the middle (median ) located protrusion or projection, the rostrum extend.

Turtles

The most striking of the many special features of the turtles ( Testudinata ) is the bony armor. The turtle can if required - protection from predators or adverse weather - completely hide it. Fossils of turtles from the Triassic show animals with incomplete armor, in one case a the ribs only loosely fitting skin tanks, in the other a plastron without carapace, but corresponds to the characteristic transformation of the ribs that of today's turtles (see origin of the turtle shell ). The " Urschildkröten " of the genera Proterochersis and only slightly younger Proganochelys from the more than 210 million year old Upper Triassic Stubensandstein southwest Germany have a modern tank, which is very similar to living today ( extant ) representative.

Structure and form

The shell of a turtle is made of the more or less strongly curved, dorsal carapace ( carapace ) and the flat, ventral plastron ( plastron ) that are connected to the sides of a bone bridge. Large openings at the front and rear end let the head and front legs or the tail and hind limbs emerge. Dorsal and ventral tanks show the same basic structure: At the bottom is a layer of permanently interconnected plates of dermal bones ( Dermalknochen, osteoderms ). These massive bones form a rigid bandage and give the tank its shape and stability., Spans a skin layer - is covered with thin plates ( scales) of horny substance ( keratin) - except for the soft-shelled turtles. These are due to their shape " Scuta " (Latin, singular Scutum ), named after the rectangular curved wooden shield of the Roman legionaries. The carapace is completely ossified in adult specimens, and especially with the shoulder girdle and the unusually high mounted, widened ribs and with parts of the pelvic girdle and the spinous processes of the spine firmly adherent. Shields the overlying horn are staggered slightly larger than the bone elements and light, the thus achieved overlap of the interstices increases the stability of the tank.

The aquatic soft-shelled turtles have no horn shields, but a flexible, leathery skin on a flat, round back plate, as they have lost the originally existing shields again in the course of their evolutionary history. The marginal bone missing in most cases also. A special development have also taken the joint turtles. A hinge-like articulation in the rear third of the carapace allows them to tank completely close.

Configurations of the dorsal shield

Streamlined sign of a sea turtle

On the carapace of soft-shelled turtles, the horn missing shields

In simple terms, let each of the bone plates and shields on their location on the carapace from the inside out into groups, the counting of the individual elements is from the front ( cranial) to the rear ( caudal ). The names of the bone plates often tally with those of the horn shields and are therefore not unique, and there is many synonyms.

Bone plates

• The unpaired, front plate in the middle (median ) is called Nuchal or neck plate (Latin nucha " neck ").
• 8 Neuralia (reference to the neural arch of the vertebra ) are continuing the Media series. Only the Neuralia are fused with the spinous processes of the spine.
• The series is completed by Pygale ( gr pyge " rump "). Above is the appearance of additional 1 to 2 Pygalplatten, the Suprapygalia possible.
• On both sides ( lateral) of the Neuralia are each 8 Costalia (Latin costa 'rib'; Syn: Pleuralia, gr pleura, " side ", " rib " ) intertwine with the ribs.
• The edge of the bone armor is on both sides of each 11 Marginalia (Latin margo " edge "). Rarely additional peripheral Supramarginalia are present, an original feature that is missing most advanced forms.

Horn shields ( Scuta )

• The unpaired, foremost median cervical or neck shield ( Syn: Cervical, Nuchal, Präcentrale; cervix Latin "neck" ) is located in front of the spinal column shields. According to some authors of the neck shield is one of the Vertebralia.
• Below are 5 vertebral or vertebral shields ( Vertebralia, Syn: Centralia ) in a median row over the spine ( vertebral columna ).
• On both sides of the vertebral shields close each 4 pleural, side, ribs or shields ( Costalia, Syn: lateralia ) to.
• The carapace and is bordered on both sides by 12 per marginal or boundary shields ( Marginalia ). Together, the two rearmost caudal shields that Postcentralia form, the Supracaudal or pygidium ( Supracaudale, syn. caudal; Latin cauda "tail ").

The often strikingly drawn and formed only a few millimeters thick Scuta show at a newly hatched turtle a single growth bands around each plate center ( areola ). During adolescence, there are further strips added, but this happens at irregular intervals and is set almost entirely in older specimens, therefore, allowed the number of growth rings no conclusion to the age. The shape of the horn shields, their number and relative position to each other, for example, the number of ribs shields touching the neck shield, vary among the species. With the help of these features can be, the species of living animals uniquely determined. But the shield relief can be very diverse. So the Scuta form in some species from one, others three longitudinal keels. In the Map turtles, for example, the center keel ( Dorsalkiel ) occurs in the vertebral shields is very clear, other species show two additional Lateralkiele along the side shields. Frequently, individual variations occur, especially in the number of shields. Such sign abnormalities are usually not genetic, but due to different incubation conditions of eggs in the nest. The species-specific data on the number of the horny shields thus corresponds to statistical averages.

The turtle shell is a stable, yet by no means insensitive structures. Immediately below the horn shields is the crisscrossed by numerous blood vessels and nerves and therefore extremely sensitive to pain periosteum of Dermalknochen. Strong mechanical action may occur tank fractures.

Function and meaning

The curvature of the carapace can vary in strength. The adapted to life in water turtles such as the neck turner turtles ( Pleurodira ) and the aquatic or amphibious living in freshwater species, the neck Berger Turtles ( Cryptodira ) have flatter Carapaces than their terrestrial representatives who Tortoises ( Testudinidae ) whose carapace a characteristic has dome- like shape. The greater the curvature of the back shell, the greater the mechanical strength and thus the protective effect. In addition, a high arched carapace for the cold-blooded animals increases the ability to store heat. But there are limitations: Types, who are forced to protect against extreme temperatures, to dig deep caves, such as steppes or Four-toed Tortoise ( Testudo horsfieldii ), have shallower tanks than those who live in more temperate regions. The carapace of the sea turtle also shows significant adaptations to habitat and lifestyle. It is flat and streamlined, and the bone portion is reduced in order to save weight.

The turtle shell is a unique development that has remained virtually unchanged for over 200 million years and has contributed significantly to the evolutionary success of this very ancient group of reptiles. Few enemies are able to overcome the shell of a full-grown turtle. Raptors let turtles from great heights fall on rocks, they too will be captured by crocodiles ( Crocodilia ). As the biggest threat but turns out the man. From the horny substance of various sea turtles, the coveted especially in the 19th century tortoiseshell can win. Although demand has fallen sharply, but at the hunting pressure to minimize the other reasons largely on the verge of extinction standing animals, more than 148 States have since 1994 ( as of 2000) in Artenschutzübereinkommen CITES obliged to ban the trade in tortoiseshell, including the wholesale Japan.

Arachnids

In the arachnids (Arachnida ) is the carapace (also Peltidium to gr - lat. Pelta " small crescent sign" ), a uniform chitinöser back plate of the fused segment tops ( tergites ) of head ( cephalon ) and chest (thorax), the may cover the front body ( the prosoma, mostly inaccurate as cephalothorax ( " head - chest " ) refers ). If the Peltidium of several pieces (with the scourge scorpions, spiders and rolling Palpenläufern ), are the names from front to back: Pro-, meso-and Metapeltidium. The bottom of the front abdomen is used in many types of a triangular ventral plate, the sternum, covered.