Trichomycterus is the largest genus of pencil catfishes with over 100 species currently described. This genus is native to South America.
This genus is defined by the lack of specializations found in other trichomycterids and is certainly polyphyletic. Although known to contain many species, Trichomycterus is poorly known with many of the known species based on brief descriptions. Many species have been described recently and many more are waiting to be described.
Some authors have tentatively defined putati
ve monophyletic assemblages within the
genus Trichomycterus based on the possession of unique morphological features. The T. brasiliensis species-complex includes T. brasiliensis, T. iheringi, T. maracaya, T. mimonha, T. potschi, T. vermiculatus, and several undescribed species apparently endemic to the main river basins draining the Brazilian Shield. However, an assemblage of species from south and southeastern Brazil is also supported that includes T. guaraquessaba, T. iheringi, T. nigricans, T. davisi, T. stawiarski, T. castroi, T. triguttatum, T. immaculatus, T. itatiayae, T. mirissumba, T. zonatus, T. naipi, T. taboba, T. papilliferus, T. mboycy, and T.
plumbeus. T. aguarague, T. alterus, T. boylei, T. ramosus, and T. belensis also form a diagnosable species assemblage.
Distribution and habitat
Species of Trichomycterus inhabit a diversity of habitats throughout South and Central America from Costa Rica in the north to Patagonia in the south, and from lowland Atlantic rainforest in the east to Andean streams in the west. A number of species of Trichomycterus are known from various mid- to high-elevation localities in western Argentina; in these upland regions the species of Trichomycterus are among the
few, or sometimes only, fishes occupying
water bodies at middle to higher elevations. About 60 nominal species are endemic to the river basins draining the Andes and hills of the Guianan Shield, and about 30 species are endemic to river basins draining the Brazilian Shield.
Despite the broad distribution of the genus, most species have limited distributions, and usually are restricted to only one river. Wide-ranging species are most likely complexes of species that are difficult to differentiate, such as the T. brasiliensis species-complex. Trichomycterus gorgona, from a small stream on Gorgona Island located west of
the Pacific coast of Colombia, is the first known trichomycterid to be endemic to an offshore island.
Six hypogean species are in the genus Trichomycterus: Trichomycterus chaberti, T. itacarambiensis, T. santanderensis, T. spelaeus, and T. uisae.
These fish are generally small, usually about 50?150 millimetres (2?6 in) SL. Species differ from one another primarily in body proportions, fin ray counts, and coloration.
There are currently 147
recognized species in this genus: 
h Genus Trichomycterus (Siluriformes: Trichomycteridae) Representing a New Body Shape for the Family". Copeia 2008
(2): 273?278. doi:10.1643/CI-06-237
. ^ Wosiacki & de Pinna (2008). "Trichomycterus igobi, a new catfish species from the rio Igua?u drainage: the largest head in Trichomycteridae (Siluriformes:
Trichomycteridae)". Neotropical Ichthyology 6 (1): 17?23. ^ a b Wosiacki, Wolmar Benjamin; Oyakawa, Osvaldo Takeshi (2005). "Two new species of the catfish genus Trichomycterus (Siluriformes: Trichomycteridae) from the rio Ribeira de Iguape Basin, Southeastern Brazil" (PDF). Neotropical Ichthyology 3 (4): 465?472. doi:10.1590/S1679-62252005000400003. http://www.ufrgs.br/ni/vol3num4%5CNI_v3n4p465-472lowr.pdf. ^ a b c d e Wosiacki, Wolmar Benjamin; Garavello, J?lio C?sar (March 2004). "Five new species of Trichomycterus from the rio Igua?u (rio Paran? Basin), southern Brazil (Siluriformes:
Trichomycteridae)". Ichthyol. Explor. Freshwaters 15 (1): 1?16. ^ Fern?ndez, Luis; Chuquihuaman?, Roberto Quispe (2007). "A new species of Trichomycterus (Siluriformes: Trichomycteridae) from the Andean Cordillera of Per?, with comments on relationships within the genus" (PDF). Zootaxa 1545: 49?57. http://www.mapress.com/zootaxa/2007f/z01545p057f.pdf. ^ Barbosa, Maria Ana?s; Costa, Wilson J. E. M. (October 2003). "Trichomycterus potschi (Siluriformes: Loricarioidei): a new trichomycterid catfish from coastal streams of southeastern
Brazil". Ichthyol. Explor. Freshwaters 14 (3): 281?287. ^ Castellanos-Morales, Cesar A. (2007). "Trichomycterus santanderensis: A new species of troglomorphic catfish (Siluriformes, Trichomycteridae) from Colombia" (PDF). Zootaxa 1541: 49?55. http://www.mapress.com/zootaxa/2007f/z01541p055f.pdf. ^ Fernandez, Luis.; Miranda, Guillermina. (November 2007). "A catfish of the genus Trichomycterus from a thermal stream in southern South America (Teleostei, Siluriformes, Trichomycteridae), with comments on relationships within the
genus". Journal of Fish Biology 71 (5): 1303?1316. doi:10.1111/j.1095-8649.2007.01589.x. ^ "New species of the catfish genus Trichomycterus (Siluriformes, Trichomycteridae) from the headwaters of the rio S?o Francisco basin, Brazil" (PDF). Zootaxa 592: 1?12. 2004. http://www.mapress.com/zootaxa/2004f/zt00592.pdf. ^ Ferrer, Juliano; Malabarba, Luiz R. (2011). "A new Trichomycterus lacking pelvic fins and pelvic girdle with a very restricted range in Southern Brazil (Siluriformes:
Trichomycteridae)" (PDF Excerpt). Zootaxa 2912: 59?67. http://mapress.com/zootaxa/2011/f/z02912p067f.pdf. ^ Fern?ndez, Luis; Schaefer, Scott A. (December 2003). "Trichomycterus yuska, a new species from high elevations of Argentina (Siluriformes: Trichomycteridae)". Ichthyol. Explor. Freshwaters 14 (4): 353?360.