Spotted Gar (Lepisosteus oculatus) (3149758934)

Ganoine or ''ganoin'' is a glassy, often multi-layered mineralized tissue that covers the

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number w ...

cranial Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

bones and fin rays in some non-teleost ray-finned fishes, such as gars,

bichir Bichirs and the reedfish comprise Polypteridae , a family of archaic ray-finned fishes and the only family in the order Polypteriformes .Helfman GS, Collette BB, Facey DE, Bowen BW. 2009. The Diversity of Fishes. West Sussex, UK: Blackwell Pu ...

s, and

coelacanth The coelacanths ( ) are fish belonging to the order Actinistia that includes two extant species in the genus ''Latimeria'': the West Indian Ocean coelacanth (''Latimeria chalumnae''), primarily found near the Comoro Islands off the east coast ...

s. It is composed of rod-like, pseudoprismatic

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common ...

crystallites, with less than 5% of organic matter. Existing fish groups featuring ganoin are

s and gars, but ganoin is also characteristic of several extinct

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

. It is a characteristic component of

ganoid scale A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as ...

s. Ganoine is an ancient feature of ray-finned fishes, being found for example on the scales of

stem group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

actinopteryigian '' Cheirolepis''. While often considered a synapomorphic character of ray-finned fishes, ganoine or ganoine-like tissues are also found on the extinct

acanthodii Acanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes), typically considered a paraphyletic group. They are currently considered to represent a grade of various fish lineages leading up to the extant Chondrichthyes, ...

. It has been suggested that ganoine is homologous to

tooth enamel Tooth enamel is one of the four major tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are dentin, ...

in vertebrates or even considered a type of enamel. Ganoine indeed contains

amelogenin Amelogenins are a group of protein isoforms produced by alternative splicing or proteolysis from the ''AMELX'' gene, on the X chromosome, and also the ''AMELY'' gene in males, on the Y chromosome. They are involved in amelogenesis, the developme ...

-like proteins and has a mineral content similar to that of

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

tooth enamel.

References

{{diversity of fish Fish anatomy Tissues (biology)