Lingulidae
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''Lingula'' is a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of 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 e ...
s within the class
Lingulata Lingulata is a class of brachiopods, among the oldest of all brachiopods having existed since the Cambrian period (). They are also among the most morphologically conservative of the brachiopods, having lasted from their earliest appearance to the ...
. ''Lingula'' or forms very close in appearance have existed possibly since the
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
. Like its relatives, it has two unadorned organo-phosphatic valves and a long fleshy stalk. ''Lingula'' lives in burrows in barren sandy coastal seafloor and feeds by filtering
detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...
from the water. It can be detected by a short row of three openings through which it takes in water (sides) and expels it again (middle).


Anatomy and morphology


Shell

A shell encloses the organs and other internal parts of the body, except for a long, fleshy stalk (or pedicle) that extends from the tail (or posterior) end of the shell. This shell has two nearly identical tan or bronze valves, that are often tinged greenish or bluegreenish. These are held together by muscles between them. The valves are secreted by two mantle folds, one on the dorsal and one on the ventral side of the body. The valves are composed of
chitin Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cell ...
, protein, and calcium phosphate and consist of about 50% organic material. The outer surface is covered by a thin glossy layer of protein called
periostracum The periostracum ( ) is a thin, organic coating (or "skin") that is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among molluscs, it is primarily seen in snails and clams, i.e. in gastropods an ...
. The high organic content of the shell makes it somewhat soft and flexible. These valves are located on the dorsal and ventral surfaces of the animal. The front (or
anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
) end of the shell has a squared off (or truncate) shape and the rear end tapers to a point where the stalk emerges. This point (called apex) is the earliest part of the valve. The shell of the young animal roughly remains the same, adding much material at the front and less at the sides. Many growth lines are visible, parallel to the margins of the shell. The valves widen slightly at the front end, forming a narrow opening (or gape), through which water is pumped in at the sides and out from the middle. The ventral valve is slightly longer and slightly more convex. The margin of the valves is fringed by chitinous tan colored bristle (or
chaeta A chaeta or cheta (; ) is a chitinous bristle or seta found on annelid worms, although the term is also frequently used to describe similar structures in other invertebrates such as arthropods. Polychaete annelids (''polychaeta'' literally me ...
e), short at the side of the valves, but much longer at the front where they assist in keeping open the access of the body cavity to the outside water. In death, the gape is closed and the bristles may be absent or short as they become brittle and darker in color when dry.


Stalk

The stalk (or pedicle) is a long white extension of the body, that emerges at the apex from between the valves, and not, as in articulate brachiopods, from a special opening in the dorsal valve. At the rear end, that is deepest in the sea bed, the skin (or
epithelium Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...
) secretes a glue-like mucus that binds to the substrate's particles, thus temporarily anchoring the animal. The very thick skin (cuticle) is not composed of cells, and is opaque, being secreted by a very thin white
epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...
, which is attached by a very thin layer of connective tissue to the white muscle inside. The muscle fibres are attached to the connective tissue and are wound like helixes. In the centre of the muscle runs an inconspicuous tube-shaped opening along the entire length, which is an extension of, and in open connection with, the body cavity within the shell. It is lined by a layer of one cell thick
mesothelium The mesothelium is a membrane composed of simple squamous epithelium, simple squamous epithelial cells of mesodermal origin, which forms the lining of several body cavities: the pleura (pleural cavity around the lungs), peritoneum (abdominopelvic ...
.


Internal organs

Ovaries have a fine texture and a tan to orange color. Male gonads are coarse-grained and creamy white.


Reproduction

Species such as '' Lingula anatina'' have a breeding season that extends from summer to fall and breed annually. Their larvae are planktonic.


Living fossil

''Lingula'' has long been considered an example of a
living fossil A living fossil is a Deprecation, deprecated term for an extant taxon that phenotypically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of or ...
; in fact, the perceived longevity of this genus led Darwin to coin this concept. This living fossil status is now considered unjustified. This status is based on the shape of the shell only, and it has been shown that this shape corresponds to a burrowing lifestyle, occurring in different brachiopod lineages, with different and evolving internal structures.


Taxonomy

The genus ''Lingula'' was created in 1791 by
Jean Guillaume Bruguière Jean Guillaume Bruguière (19 July 1749 – 3 October 1798) was a French physician, zoologist and diplomat. Biography Bruguière was born in Montpellier, France, on 19 July 1749.Comptes rendus du Congrès national des sociétés savantes: Se ...
. George Shaw describe ''Mytilus rostrum'' in 1798, but this species was later assigned to ''Lingula''. In 1801
Jean-Baptiste Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist, biologist, academic, and soldier. He was an early proponent of the idea that biologi ...
described ''L. anatina'', its type species.


Possible etymologies

''Lingula'' is probably derived from the
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
word for tongue "lingua" and a diminutive suffix -ula, so small tongue. Alternatively it may be derived from the Latin word for spoon (Lingula) directly. The origin of the
epithet An epithet (, ), also a byname, is a descriptive term (word or phrase) commonly accompanying or occurring in place of the name of a real or fictitious person, place, or thing. It is usually literally descriptive, as in Alfred the Great, Suleima ...
''anatina'' is not known, but in Latin "anatina" means "belonging to the duck", possibly due to its resemblance to a duck bill. Another possible derivation could be from the French ''anatife'' ('
goose barnacle Goose barnacles, also called percebes, turtle-claw barnacles, stalked barnacles, gooseneck barnacles, are filter-feeding crustaceans that live attached to hard surfaces of rocks and flotsam in the ocean intertidal zone. Goose barnacles form ...
'), for its likeness.


Reassigned species

The following species, previously assigned to ''Lingula'' are now considered better placed in other genera: * ''L. albida'' = '' Glottidia albida'' * ''L. alveolata'' = †'' Dignomia alveolata'' * ''L. attenuata'' = †'' Palaeoglossa attenuata'' * ''L. audebarti'' = '' Glottidia audebarti'' * ''L. criei'' = †'' Tomasina criei'' * ''L. davisii'' = †'' Lingulella davisii'' * ''L. imbituvensis'' = †'' Langella imbituvensis'' * ''L. lesueuri'' = †'' Ectenoglossa lesueuri'' * ''L. nebrascensis'' = †'' Trigonoglossa nebrascensis'' * ''L. pinnaformis'' = †'' Lingulepis pinnaformis'' * ''L. plumbea'' = †'' Monobilina plumbea'' * ''L. polita'' = †'' Dicellomus polita'' * ''L. semen'' = '' Glottidia semen'' * ''L. subspatulata'' = †'' Barroisella campbelli'' * ''L. williamsana'' = †'' Lingulipora williamsana''


Extinct species

The following are extinct ''Lingula'' species. *? †'' Lingula tenuis'' Sowerby *†'' Lingula dregeri'' Andreae, 1893 *†'' Lingula waikatoensis'' Pen, 1930 *? †'' Lingula eocenica'' Moroz & Ermokhyna, 1990 Extinct ''Glottidia'' or ''Lingula'' species: *'' Glottidia dumortieri'' (Nyst, 1843) *'' Glottidia antarctica'' (Buckman, 1910) *'' Glottidia inexpectans'' Olsson, 1914 *'' Glottidia bravardi'' Figueiras & Martinez, 1995


Ecology

''Lingula'' inhabits a vertical burrow in soft sediments, with the front face upward near the surface of the sea bed. The cilia on the lophophore create a current through the mantle cavity, which ensures the supply of food particles and oxygen. Although ''Lingula'' is one of the most euryhaline brachiopods, it tolerates only moderate salinity variations (down to about half seawater salt concentration) and is optimally marine.


Cuisine

It is eaten in various parts of the world, such as Vietnam. Because they live in mud, they first need to be cleansed in fresh water. The most popular part is the stalk, which is crunchy to eat. They are also fermented.Odd-looking lingula forms soul of Ha Tien cuisine
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Gallery

File:Lingula anatina 002.png, The sole evidence of the presence of ''Lingula anatina'' is a small three-lobed slit on the surface of the substrate File:Lingula anatina 001.png, ''Lingula anatina'' in tubes in the sand, lateral and dorsal or ventral views; the dotted line indicates position in retraction File:Lingula anatina 003.png, ''Lingula anatina'': animal removed from the shell, mantle reflected, coiled arms separated slightly; a) mouth (marginal setae omitted); ventral aspect, three-quarter face File:Lingula anatina 004.png, ''Lingula anatina'': interior of the valve showing muscle scars; V. peduncle valve D. brachial valve


References


External links



* *
Brachiopoda world databaseBrachNet
{{DEFAULTSORT:Lingula (Genus) Brachiopod genera Extant Cretaceous first appearances Lingulata Fossils of Georgia (U.S. state) Paleozoic life of Ontario Paleozoic life of Alberta Paleozoic life of Manitoba Paleozoic life of the Northwest Territories Paleozoic life of Nova Scotia Paleozoic life of Nunavut Paleozoic life of Quebec Paleozoic life of Yukon