The Glanapteryginae are a

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive, ...

es (order Siluriformes) of the family

Trichomycteridae Trichomycteridae is a family of catfishes commonly known as pencil catfishes or parasitic catfishes. This family includes the candiru fish (''Vandellia cirrhosa''), feared by some people for its alleged habit of entering into the urethra of hum ...

. It includes four

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

, ''

Glanapteryx ''Glanapteryx'' is a genus of catfishes native to South America. Taxonomy ''Glanapteryx'' is a monophyletic genus. ''Glanapteryx'' has been proposed as the sister group to a clade composed of '' Pygidianops'' and '' Typhlobelus'', with '' L ...

'', '' Listrura'', '' Pygidianops'', and '' Typhlobelus''.

Phylogeny

Monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...

of the subfamily is supported by five

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

involving reductions in the fins, caudal skeleton, and laterosensory system. It has been proposed that the sister group to this subfamily is the

Sarcoglanidinae The Sarcoglanidinae are a subfamily of catfishes (order Siluriformes) of the family Trichomycteridae. It includes six genera: '' Ammoglanis'', '' Malacoglanis'', '' Microcambeva'', '' Sarcoglanis'', '' Stauroglanis'', and '' Stenolicmus''. Taxo ...

. ''Listrura'' is the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

to the remainder of the subfamily. ''Glanapteryx'' is sister to a clade formed by the sister taxa ''Pygidianops'' and ''Typhlobelus''.

Distribution

''Glanapteryx'', ''Pygidianops'', and ''Typhlobelus'' are distributed in the

Orinoco The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers , with 76.3 percent of it in Venezuela and the remainder in Colombia. It is the fourth largest river in the wor ...

and

Amazon River basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Bolivi ...

s. ''Listrura'' species are from

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, outside of the Amazon River basin. However, the distribution of glanapterygines may be greater than previously thought.

Description

Most of the subfamily is constituted by 'miniaturized' species. Though miniaturized fish usually refers to fish that do not reach 25.4 mm (1.0 in)

standard length Fish measurement is the measuring of individual fish and various parts of their anatomies. These data are used in many areas of ichthyology, including taxonomy and fisheries biology. Overall length * Standard length (SL) is the length of a fish m ...

, ''Glanapteryx'' and ''Typhlobelus'' have been considered 'elongated miniatures' due to their

paedomorphic Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the physiological, or somatic, development of an organism, typically an animal. Neoteny is found in modern humans compared ...

features and small head sizes, despite their lengths exceeding an inch. ''Pygidianops'' and ''Typhlobelus'' are the most modified glanapterygines, sharing extreme reduction or loss of pigmentation, fins, laterosensory system, and eyes; they are also miniaturized, yet retain the well-

ossified Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by Cell (biology), cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes ...

skeleton comparable in both bone differentiation and degree of calcification to that observed in larger trichomycterids. All four of these genera are currently monophyletic.

Habitat

Glanapterygine phylogeny indicates the evolution of the group followed a trend of decreasing dependence on leaf litter and increasing association with sand. ''Listrura'' species occur in shallow-water leaf-litter deposits underlain by mud or deeper layers of leaf litter. Little is known about the habitats of the species of ''Glanapteryx'', but information available indicates they have been collected in association with leaf litter underlain with sand. By contrast, ''Pygidianops'' and ''Typhlobelus'' are entirely disassociated from leaf litter, and occupy exclusively clear water, loose sand; some species have been found to live exclusively in the substratum of the sand (rather than on the sand surface or in the water column above the sand), which could be the first vertebrates identified to be part of the

meiofauna Meiobenthos, also called meiofauna, are small benthic invertebrates that live in both marine and fresh water environments. The term ''meiofauna'' loosely defines a group of organisms by their size, larger than microfauna but smaller than macrofau ...

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

organisms. The latter two genera are more specialized for this lifestyle than any other catfishes, as evidenced by their loss of morphological traits. These two species also have paired keels, called metapleural keels, formed by long ridges of stiffened integument, extend along the entire ventral margin of the abdomen, ending posteriorly shortly posterior to the anus. These keels probably serve to stabilize the body while moving in sand.

References

{{Taxonbar, from=Q5566598 Trichomycteridae Fish of South America Fish of the Amazon basin Fauna of Brazil Ray-finned fish subfamilies Taxa named by George S. Myers