tororo has nine branchiostegal rays, a condition not present T. igobi, T. crassicaudatus and T. stawiarski also unusual among trichomycterids 
Even so, the aforementioned presumably derived character states shared by the species herein proposed as belonging to the Trichomycterus stawiarski group (Table 1) suggest their close relationship and the reduced number of branchiostegal rays in T. ytororo could be interpreted as a homoplastic feature. However, a comprehensive phylogenetic analysis of the genus is still needed to assess if those character states are more parsimoniously attributed to common ancestry or parallelisms and to test the monophyly of this putative clade.
Trichomycterus crassicaudatus, T. igobi, and T stawiarski are endemic to the Iguazú (or Iguaçu, in Brazil) River basin, a left bank tributary of the Paraná River, while T. ytororo inhabits a downstream section of the same basin (Fig 5). Curiously, all these species are known from few collecting sites or only from their type localities (as T. ytororo), possibly indicating some ecological constraints in their distributions.
We thank Pablo Pereyra (FML) for figure 3. We thank Celeste Kummer for assistance with the radiograph of the holotype and paratypes. Mercedes Azpelicueta (CONICET) for constant support. This work was possible due to the invaluable help of Diego Baldo and Juan Martín Ferro. We thank Pedro Sanchez for logistical assistance in the field. Ministerio de Ecología, Misiones for collecting permits. We thank Carlos DoNascimiento (IAvH) and an anonymous reviewer for careful reviews in the manuscript. We are also thankful to Fundación Miguel Lillo, CONICET (PIP–11420110100301 to JMM) and FONCyT (PICT–2011–0992 to JMM); CNPq (Proc. 152354/2016-6 to JF).
- Conceptualization: GA JMM GET MB FA JF.
- Data curation: GET JF.
- Formal analysis: JF GET GA JMM.
- Funding acquisition: JMM JF.
- Investigation: GET JF.
- Resources: GET GA JMM.
- Visualization: FA GET JMM.
- Writing – original draft: GET JMM JF.
- Writing – review & editing: GA MB FA.
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