parent_taxon acipenser
Sturgeon is the common name for the 27 species of fish belonging to the family ___MASK62___ . Their evolution dates back to the Triassic some 245 to 208 million years ago . The family is grouped into four genera : " Acipenser ", " Huso ", " Scaphirhynchus " and " Pseudoscaphirhynchus ". Four species may now be extinct . Two closely related species , " Polyodon spathula " ( paddlefish ) and " Psephurus gladius " ( Chinese paddlefish , possibly extinct ) are of the same order , Acipenseriformes , but are in the family Polyodontidae and are not considered to be " true " sturgeons . Both sturgeons and paddlefish have been referred to as " primitive fishes " because their morphological characteristics have remained relatively unchanged since the earliest fossil record . Sturgeons are native to subtropical , temperate and sub - Arctic rivers , lakes and coastlines of Eurasia and North America . Sturgeons are long - lived , late - maturing fishes with distinctive characteristics , such as a heterocercal caudal fin similar to that of sharks , and an elongated spindle - like body that is smooth - skinned , scaleless and armored with 5 lateral rows of bony plates called scutes . Several species can grow quite large , typically ranging 7  12 feet ( 2 - 3 m ) in length . The largest sturgeon on record was a Beluga female captured in the Volga estuary in 1827 , weighing and long . Most sturgeons are anadromous bottom - feeders which migrate upstream to spawn but spend most of their lives feeding in river deltas and estuaries . Some species inhabit freshwater environments exclusively while others primarily inhabit marine environments near coastal areas , and are known to venture into open ocean . ___MASK72___ is an order of basal ray - finned fishes that includes the sturgeons and paddlefishes , as well as some extinct families . Binomial nomenclature ( also called binominal nomenclature or binary nomenclature ) is a formal system of naming species of living things by giving each a name composed of two parts , both of which use Latin grammatical forms , although they can be based on words from other languages . Such a name is called a binomial name ( which may be shortened to just " binomial "), a binomen or a scientific name ; more informally it is also called a Latin name . The first part of the name identifies the genus to which the species belongs ; the second part identifies the species within the genus . For example , humans belong to the genus " ___MASK15___ " and within this genus to the species " ___MASK15___ sapiens ". The " formal " introduction of this system of naming species is credited to Carl Linnaeus , effectively beginning with his work " Species Plantarum " in 1753 . But Gaspard Bauhin , in as early as 1623 , had introduced in his book " Pinax theatri botanici " ( English , " Illustrated exposition of plants ") many names of genera that were later adopted by Linnaeus . ___MASK40___ is genus of sturgeons . With 17 species , many of which are threatened , it is the largest genus in the order ___MASK72___ . In biology , an organism is any contiguous living system , such as an ___MASK97___ , plant , fungus , archaeon , or bacterium . All known types of organisms are capable of some degree of response to stimuli , reproduction , growth and development and homeostasis . An organism consists of one or more cells ; when it has one cell it is known as a unicellular organism ; and when it has more than one it is known as a multicellular organism . Most unicellular organisms are of microscopic scale and are thus loosely described as microorganisms . Humans are multicellular organisms composed of many trillions of cells grouped into specialized tissues and organs . A genus ( genera ) is a taxonomic rank used in the biological classification of living and fossil organisms in biology . In the hierarchy of biological classification , genus comes above species and below family . In binomial nomenclature , the genus name forms the first part of the binomial species name for each species within the genus .