Re-validation of Otocinclus arnoldi Regan and reappraisal of Otocinclus phylogeny (Siluriformes: Loricariidae)

Abstract

Otocinclus arnoldi from the La Plata basin is resurrected from the synonymy of O. flexilis described from the rio Jacuí drainage, based on three distinguishing features: the possession of five branched pectoral-fin rays, the larger number of enlarged odontodes on the tip of the parieto-supraoccipital posterior process, and having the prootic involved in the contact with the hyomandibular articular condyle. These species are also compared to O. mimulus, a third species described from the Paraná River basin, and the three species are rediagnosed. A reassessment of the phylogenetic relationships of all species of Otocinclus shows a well-supported clade composed of (O. xakriaba ((O. mimulus, O. arnoldi) (O. affinis, O. flexilis))) from the eastern-draining river basins of the Brazilian Shield as sister-group to a clade including all remaining Otocinclus species which are distributed on a wide lowland area of the Amazonas, Paraguay, and Orinoco basins.Otocinclus arnoldi da bacia do rio da Prata é revalidada da sinonímia de O. flexilis, descrito da bacia do rio Jacuí, baseado em três características distintivas: a presença de cinco raios ramificados na nadadeira peitoral, o maior número de odontódeos hipertrofiados na ponta do processo posterior do parieto-supraoccipital, e por ter o proótico envolvido no contato com o côndilo articular do hiomandibular. Essas espécies são também comparadas com O. mimulus, outra espécie descrita da bacia do rio Paraná, e as três espécies são re-diagnosticadas. Uma nova análise filogenética de todas as espécies de Otocinclus revelou um clado bem suportado composto por (O. xakriaba ((O. mimulus, O. arnoldi) (O. affinis, O. flexilis))) dos rios do escudo Brasileiro que drenam para leste, como grupo-irmão de um clado que inclui todas as demais espécies de Otocinclus que são distribuídas em uma grande área baixa das bacias do Amazonas, Paraguai e Orinoco.

An appraisal of the phylogenetic relationships of Hypoptopomatini cascudinhos with description of two new genera and three new species (Siluriformes: Loricariidae)

“…1b). As previously noted (Schaefer, 1997;Lehmann et al, 2010), all Otocinclus have a reduced or completely absent ridge on the ventral surface of the lateral ethmoid (state 2; Fig. 1c).…”

“…The phylogenetic relationships uncovered by Lehmann et al (2010) did not gain much resolution when compared to previous analyses published by Schaefer (1997) despite the addition of six morphological characters.…”

“…The present analysis found Otocinclus as a wellsupported clade and sister to all other Hypoptopomatini, corroborating Schaefer (1991; and Lehmann et al (2010). Conflicting with the results of Schaefer (1991;, but corroborating results by Rodriguez et al (2015), Acestridium and Niobichthys formed a clade sister to the remaining members of the tribe.…”

“…Within Hypoptopomatini, the most densely studied genus is Otocinclus (Schaefer, 1997;Britto, Moreira, 2002;Axenrot, Kullander, 2003;Lehmann et al, 2010). The phylogenetic relationships uncovered by Lehmann et al (2010) did not gain much resolution when compared to previous analyses published by Schaefer (1997) despite the addition of six morphological characters.…”

Redescription of Astyanax multidensEigenmann, 1908 (Characiformes: Characidae), a small characid of the Brazilian Amazon

“…Despite of the high diversity of the family Characidae, these were the first cases of Batesian mimicry described for the small-sized Characidae. (Axenrot & Kullander, 2003;Lehmann et al 2010), Brachyrhamdia imitator Myers and Corydoras melanistius Regan (Axenrot & Kullander, 2003).…”