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Brachiopoda  (Armfüßer)   Lower Cambrian–Recent

As a rule, the caterpillars reach shell sizes of a maximum of 5 centimeters, while fossil species can reach up to 30 centimeters, and especially in the case of the atremata such as Lingula, the stem can also be up to 30 centimeters long. The most striking feature of the crescent is the two-lobed shell, which is divided into a dorsal and a ventral shell. Although they are similar to the mussels on the outside, they can be recognized immediately at the position of the plane of symmetry. These pass through them vertically through the single flap and divide them into two symmetrical halves, while it runs along the shell edge with mussels. Above all, the shells can be shaped very differently in the case of the fossil representatives. Thus, in addition to the convex biconvex shells, which are arched in both directions, which the majority of the animals possess, there are concave-convex and aberrant forms which deviate from the normal form. In some species, the shape changes in the course of development from a convex-concave form to a biconvex, in which case one speaks of resupinant housings. In most species, both flaps are highly calcified and covered with an organic layer, the periosteum. Below these are alternating layers of calcium carbonate (calcite) and protein skins. In some species there is a layer of prism-shaped calcite crystals. The shells may have fine channels, through which protuberances of the mantle are covered with secreet cells, the so-called caeca. Such a tray is referred to as a "punctate" tray. Some original species such as Lingula, on the other hand, have a slightly calcified and flexible shell of chitin lamellae and calcium phosphate. The two halves of the cup are held together by a strong musculature, the most important parts of which are the "opener" and the "closer". These muscles work against each other and allow opening and closing of the bowls. There is also a hinge in the articulata, so the two shells are articulated (hence the term articulata). On the outside of the shell are bristles (Setae). The opening angle of the flaps depends on the species and can be between 7 ° for Gryphus species and 45 ° for Platidia species. In the center of the animal is attached the named Armapparat (Lophophor), which is often supported by a calcareous skeleton on the dorsal or arm shell, the lophophore skeleton or brachidium, and with which the animal feeds and breathes food from the water . The food reaches the digestive system via the centrally located and slit-shaped mouth. The body is surrounded by a two-lobed sheath, which secures the shell materials on the outer side. The soft body, including the lophophores, is completely enclosed by both housing flaps. The internal organs lie in the rear housing area, the front consists of a cave cavity, into which the lophophores project. When the flaps are closed, the lophophore is inserted into the filter chamber and does not re-open until the flaps are opened again.
root  Brachiopoda (Armfüßer) Lower Cambrian–Recent
   Craniata  (Schädeltiere)   Craniata
   Lingulata  (Lingulata)   Lingulata
   Rhynchonellata  (Rhynchonellata)   Rhynchonellata
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