A hinge line is an imaginary longitudinal line along the dorsal edge of the shell of a bivalve mollusk where the two valves hinge or articulate. The hinge line can easily be perceived in these images of a mussel shell and an ark shell. [1] [2] [3]
The hinge teeth, structures which control the articulation of the valves, are often but not always situated along the hinge line.
Bivalvia, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bivalves have no head and they lack some usual molluscan organs, like the radula and the odontophore. The class includes the clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. The majority are filter feeders. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment, where they are relatively safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some bivalves, such as the scallops and file shells, can swim. Shipworms bore into wood, clay, or stone and live inside these substances.
The Rostroconchia is a class of extinct molluscs dating from the early Cambrian to the Late Permian. They were initially thought to be bivalves, but were later given their own class. They have a single shell in their larval stage, and the adult typically has a single, pseudo-bivalved shell enclosing the mantle and muscular foot. The anterior part of the shell probably pointed downward and had a gap from which the foot could probably emerge. Rostroconchs probably lived a sedentary semi-infaunal lifestyle. There were probably more than 1,000 species of members of this class.
The taxonomic order Rhynchonellida is one of the two main groups of living articulate brachiopods, the other being the order Terebratulida. They are recognized by their strongly ribbed wedge-shaped or nut-like shells, and the very short hinge line.
A valve is each articulating part of the shell of a mollusc or another multi-shelled animal such as brachiopods and some crustaceans. Each part is known as a valve or in the case of chitons, a "plate". Members of two classes of molluscs, the Bivalvia (clams) and the Polyplacophora (chitons), have valves.
A bivalve shell is part of the body, the exoskeleton or shell, of a bivalve mollusk. In life, the shell of this class of mollusks is composed of two hinged parts or valves. Bivalves are very common in essentially all aquatic locales, including saltwater, brackish water, and freshwater. The shells of bivalves commonly wash up on beaches and along the edges of lakes, rivers, and streams. Bivalves by definition possess two shells or valves, a "right valve" and a "left valve", that are joined by a ligament. The two valves usually articulate with one another using structures known as "teeth" which are situated along the hinge line. In many bivalve shells, the two valves are symmetrical along the hinge line—when truly symmetrical, such an animal is said to be equivalved; if the valves vary from each other in size or shape, inequivalved. If symmetrical front-to-back, the valves are said to be equilateral, and are otherwise considered inequilateral.
The grooved carpet shell, or Palourde clam, Ruditapes decussatus, or Venerupis decussatus, is a clam in the family Veneridae. It is distributed worldwide and is highly prized due to its ecological and economic interest. It has been proposed as a bioindicator.
Brachiopods, phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major categories are traditionally recognized, articulate and inarticulate brachiopods. The word "articulate" is used to describe the tooth-and-groove structures of the valve-hinge which is present in the articulate group, and absent from the inarticulate group. This is the leading diagnostic skeletal feature, by which the two main groups can be readily distinguished as fossils. Articulate brachiopods have toothed hinges and simple, vertically oriented opening and closing muscles. Conversely, inarticulate brachiopods have weak, untoothed hinges and a more complex system of vertical and oblique (diagonal) muscles used to keep the two valves aligned. In many brachiopods, a stalk-like pedicle projects from an opening near the hinge of one of the valves, known as the pedicle or ventral valve. The pedicle, when present, keeps the animal anchored to the seabed but clear of sediment which would obstruct the opening.
Flexopecten felipponei is a species of saltwater scallop, a marine bivalve mollusk in the family Pectinidae, the scallops.
Juliidae, common name the bivalved gastropods, is a family of minute sea snails, marine gastropod mollusks or micromollusks in the superfamily Oxynooidea, an opisthobranch group.
Chlamys hastata, the spear scallop, spiny scallop or swimming scallop, is a species of bivalve mollusc in the family Pectinidae found on the west coast of North America from the Gulf of Alaska to San Diego, California. A limited number of these scallops are harvested by divers or by narrow trawls off the west coast of Canada.
Anodontia alba, or the buttercup lucine, is a species of bivalve mollusc in the family Lucinidae. It can be found along the Atlantic coast of North America, its range extending from North Carolina in the United States to the West Indies.
Fordillidae is an extinct family of early bivalves and one of two families in the extinct superfamily Fordilloidea. The family is known from fossils of early to middle Cambrian age found in North America, Greenland, Europe, the Middle East, Asia, and Australia. The family currently contains two genera, Fordilla and Pojetaia, each with up to three described species. Due to the size and age of the fossil specimens, Fordillidae species are included as part of the Turkish Small shelly fauna.
Fordilloidea is an extinct superfamily of early bivalves containing two described families, Fordillidae and Camyidae and the only superfamily in the order Fordillida. The superfamily is known from fossils of early to middle Cambrian age found in North America, Greenland, Europe, the Middle East, Asia, and Australia. Fordillidae currently contains two genera, Fordilla and Pojetaia each with up to three described species while Camyidae only contains a single genus Camya with one described species, Camya asy. Due to the size and age of the fossil specimens, Fordillidae species are included as part of the Turkish Small shelly fauna.
The umbo is the vaguely defined, often most prominent, highest part of each valve of the shell of a bivalve or univalve mollusc. It usually contains the valve's beak, the oldest point of the valve, and its degree of prominence and position relative to the hinge line are sometimes helpful in distinguishing bivalve taxa. The umbo forms while the animal is a juvenile, and radial growth subsequently proceeds around that area. The umbo is situated above the hinge line. In those bivalves where the umbones do not protrude, as is the case for example in some mussels, the umbones can nonetheless usually be readily identified by examining the concentric growth lines of the shell.
Hinge teeth are part of the anatomical structure of the inner surface of a bivalve shell, i.e. the shell of a bivalve mollusk. Bivalves by definition have two valves, which are joined together by a strong and flexible ligament situated on the hinge line at the dorsal edge of the shell. In life, the shell needs to be able to open slightly to allow the foot and siphons to protrude, and then close again, without the valves moving out of alignment with one another. To make this possible, in most cases the two valves are articulated using an arrangement of structures known as hinge teeth. Like the ligament, the hinge teeth are also situated along the hinge line of the shell, in most cases.
A resilifer is a part of the shell of certain bivalve mollusks. It is either a recess or a process, the function of which is the attachment of an internal ligament, which holds the two valves together.
A prodissoconch is an embryonic or larval shell which is present in the larva of a bivalve mollusk. The prodissoconch is often but not always smooth, and has no growth lines. It is sometimes still present and visible in the adult shell, if there has been no erosion of the shell in that area.
A hinge ligament is a crucial part of the anatomical structure of a bivalve shell, i.e. the shell of a bivalve mollusk. The shell of a bivalve has two valves and these are joined by the ligament at the dorsal edge of the shell. The ligament is made of a strong, flexible and elastic, fibrous, proteinaceous material which is usually pale brown, dark brown or black in color.
The adductor muscles are the main muscular system in bivalve mollusks. In many parts of the world, when people eat scallops, the adductor muscles are the only part of the animal which is eaten. Adductor muscles leave noticeable scars or marks on the interior of the shell's valves. Those marks are often used by scientists who are in the process of identifying empty shells to determine their correct taxonomic placement.
In anatomy, a resilium is part of the shell of certain bivalve mollusks. It is an internal ligament, which holds the two valves together and is located in a pit or depression known as the resilifer.
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