''Pseudexostoma'' 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 ...

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Sisoridae Sisoridae is a family of catfishes. These Asian catfishes live in fast-moving waters and often have adaptations that allow them to adhere to objects in their habitats. The family includes about 235 species. Taxonomy The family Sisoridae is recog ...

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. These species are restricted to the upper

Salween The Salween is a Southeast Asian river, about long, flowing from the Tibetan Plateau south into the Andaman Sea. The Salween flows primarily within southwest China and eastern Myanmar, with a short section forming the border of Myanmar and Tha ...

(

Nujiang River The Salween is a Southeast Asian river, about long, flowing from the Tibetan Plateau south into the Andaman Sea. The Salween flows primarily within southwest China and eastern Myanmar, with a short section forming the border of Myanmar and Tha ...

) and one upper branch of the

Irrawaddy Irrawaddy or Ayeyarwady may refer to: *Irrawaddy River, the main river of Burma *Irrawaddy Delta, a rice growing region of the country *Irrawaddy, an alternative spelling of Ayeyarwady Region, an administrative division of Burma *''The Irrawaddy'' ...

( Dayinjiang River) in

. ''P. brachysoma'' is known only from the middle and lower Nujiang River. ''P. yunnanensis'' is only known from the upper Dayinjiang. These rivers were once connected, but are now separated. Also, the environment and temperature of the Nujiang River became greatly different between the northern and southern areas, leading to speciation.

Taxonomy

''Glyptosternum yunnanesis'' was first described in 1935. However, due to its unique teeth, a separate genus ''Pseudexostoma'' was erected in 1979 for this species. The same year, a subspecies of ''P. yunnanensis'' was described, ''P. y. brachysoma''. However, it has become apparent that these two groups represent different species. Also, a third species, ''P. longipterus'', was described in 2007.Zhou, W., Yang, Y., Li, X. & Li, M.-H. (2007)
A review of the catfish genus ''Pseudexostoma'' (Siluriformes: Sisoridae) with description of a new species from the upper Salween (Nujiang) basin of China.
''Raffles Bulletin of Zoology, 55 (1): 147-155.'' Results obtained by Yang ''et al.'', 2016 showed that ''P. longipterus'' cannot be distinguished from ''P. brachysoma'' from either morphological or molecular analyses and that the former name should thus be considered a

junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...

of the latter.Yang, K., Jiang, W., Chen, X., Zhou, W. & Yang, J. (2016): An integrative approach to reappraising species validity in ''Pseudexostoma'' (Teleostei: Sisoridae). ''Zootaxa, 4158 (3): 352–366.''

Species

There are currently three recognized species in this genus: * '' Pseudexostoma brachysoma'' X. L. Chu, 1979 * '' Pseudexostoma longipterus'' Zhou, Yang, Li & Li, 2007 * '' Pseudexostoma yunnanensis'' ( T. L. Tchang, 1935)

Description

These

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

have a continuous groove behind the lip,

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

openings not extending onto the underside,

heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. Human dentition is heterodont and diphyodont as an example. In vertebrates, heterodont pertains to animals wher ...

dentition in both jaws with outer teeth shovel-shaped and sparsely arranged in one or two rows and inner teeth conical and numerous, the tooth patches separated in upper jaw, and 16–18 branched pectoral rays.Thomson, A.W. & Page, L.M. (2006)
Genera of the Asian Catfish Families Sisoridae and Erethistidae (Teleostei: Siluriformes).
''Zootaxa, 1345: 1–96.'' The lips are thick, fleshy and

papilla Papilla (Latin, 'nipple') or papillae may refer to: In animals * Papilla (fish anatomy), in the mouth of fish * Papilla (worms), small bumps on the surface of certain worms * Basilar papilla, a sensory organ of lizards, amphibians and fish * ...

ted. The paired

fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. F ...

are plaited to form an adhesive apparatus. Species of this genus have a moderately compressed body. The head is depressed and broad; it appears triangular from the side and with a rounded snout from above. The eyes are small and ovoid, located at the middle of the dorsal surface of the head. The mouth is transverse and inferior, with the teeth exposed when the mouth is closed. The teeth are embedded in the skin, shovel-shaped, with the tips exposed and arranged in irregular rows. The gill openings are narrow. The dorsal surface is smooth without

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projectio ...

s. There are four pairs of

barbels In fish anatomy and turtle anatomy, a barbel is a slender, whisker like sensory organ near the mouth (sometimes called whiskers or tendrils). Fish that have barbels include the catfish, the carp, the goatfish, the hagfish, the sturgeon, the z ...

. The

adipose fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only b ...

base is not connected to the

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

. The caudal fin is emarginate with the upper lobe smaller than the lower lobe. The

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelia ...

is midlateral and complete. Species of this genus are grey black on the dorsal surface and grey yellow on the ventral region; the caudal fin is grey black with an irregular, small, yellow patch in the middle and the other fins are grey yellow along the distal edge. ''Pseudexostoma'' grow to about SL. These species have three notches on the posterior margin of the lower lip. However, in ''P. yunnanensis'', the notches are all the same depth, while in the other two species the middle notch is shallower in depth than the lateral notches. The two median lobes formed by these notches are the same length of the lateral lobes of the lips in ''P. yunnanensis'', but they are longer in the other two species. ''P. yunnanensis'' also has more pelvic fin rays (5 vs. 3–4), a shorter adipose fin base, a deeper and longer

caudal peduncle Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

, more teeth in the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

ry tooth band (18–22 vs. 16–18) that are divided into two partially connected patches instead of two isolated patches. ''P. longipterus'' has longer pectoral, pelvic, and caudal fins as compared to its congeners.

References

{{Taxonbar, from=Q7254359 Sisoridae Fish of Asia Fish of China Freshwater fish genera Catfish genera