Isbrücker et al. (2001) describe Ancistomus for Hemiancistrus snethlegae. I have recently added H. snethlagae to my analysis, and it comes out with other Hemiancistrus (although I have as yet been unable to examine the type species, H. medians). Apparently, the only diagnostic characteristic provided by Isbrücker et al. is that Ancistomus has more teeth; however, tooth number varies widely, and the species that is almost certainly the sister to Ancistomus, H. spilomma,has manyt fewer teeth.

There have recently been several Hemiancistrus described. Cardoso and Lucinda (2003) described three species from the Tocantins (H. spilomma, H. spinosissimus, and H. micromattos. I cannot find any differences between these three species and the differences stated in the text do not work, so I am treating only H. spilomma as valid. Cardoso with coauthors also described a group of species from Southeastern Brazil that are very interesting. The ranges of these species are currently disjunct from all other Hemiancistrus and the similarPeckoltia, and the one species I have analyzed was sister to all other ancistrins. So, this group may be a new genus. Hemiancistrus landoni also comes out separate from all other Hemiancistrus and is the sister to all other ancistrins except the SE Brazil species, and is treated on a separate page as it is likely a new genus. Many undescribed species remain to be described.

The taxonomy presented below is different than what I have published, but it represents my current belief as to what Hemiancistrus is. This belief, however, seems to change daily. I have moved Peckoltia oligospila and P. sabaji to Hemiancistrus in accordance with phylogenetic analysis and the diagnosis provided below.

Ancistomus Isbrücker and Seidel, 2001

• H. chlorostictus Cardoso and Malabarba 1999
• H. fuliginosus Cardoso and Malabarba 1999
• H. guahiborum Werneke, Armbruster, Lujan and Taphorn 2005
• H. macrops (Lütken 1874)
• H. medians (Kner 1854)
• H. megalopteryx Cardoso 2004
• H. meizospilos Cardoso and da Silva 2004
• H. micromattos Cardoso and Lucinda 2003 (Synonym of H. spilomma)
• H. oligospilus (Günther 1864)
• H. punctulatus Cardoso and Malabarba 1999
• H. sabaji (Armbruster 2003)
• H. spilomma Cardoso and Lucinda 2003
• H. spinosissimus Cardoso and Lucinda 2003 (Synonym of H. spilomma)
• H. votouro Cardoso and da Silva 2004
• H. snethlageae (Steindachner 1911)
• H. subviridis Werneke, Sabaj, Lujan, and Armbruster 2005

Hemiancistrus is not a monophyletic group.

Hemiancistrus is an elusive genus.  I am not fully confident that the species referred to Hemiancistrus form a monophyletic group.  Because I am unsure whether the specimens used in the phylogenetic study form a monophyletic group with H. medians, I defer discussion of Hemiancistrus until it can be further analyzed.

Hemiancistrus differs from most of the ancitrins except Baryancistrus, Panaque, Peckoltia, some Parancistrus and Hypancistrus by lacking odontodes on the opercle. Among that group, it differs from Baryancistrus and Parancistrus by not having the dorsal-fin membrane expanded posteriorly (except for an undescribed species which differs from Baryancistrus by lacking spots and from Parancistrus by having restricted gill openings), from Panaque by having viliform teeth (vs. spoon-shaped teeth or elongated spoon-shaped teeth), and from Peckoltia by having light or dark spots or no spots (vs. dorsal saddles and spots, if present, restricted to head, abdomen and fins).

Prefers flowing-water habitats in medium to large rivers.

From the Guyanas, the Negro and Orinoco and the southern Amazonian tributaries. A likely undescribed genus currently in Hemiancistrus is found in coastal drainages of extreme southeastern Brazil.

Armbruster, J.W. 1997. Phylogenetic relationships of the sucker-mouth armored catfishes (Loricariidae) with particular emphasis on the Ancistrinae, Hypostominae, and Neoplecostominae. Unpubl. Ph.D. dissertation. University of Illinois, Urbana-Champaign. 409 pp.

Cardoso, A. R. and P.H.F. Lucinda. Three new species of Hemiancistrus (Teleostei: Siluriformes: Loricariidae) from the rio Tocantins basin with comments on the genus. Ichthyological Exploration of Freshwaters 12:319-332.