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.
Highlights
Otocinclus flexilis Cope, 1894 was described from the rio Jacuí, Rio Grande do Sul State, Brazil, based on a syntype series with two lots and 17 specimens, collected by Herbert H
All examined specimens from the La Plata basin (285 specimens, including the holotype of O. arnoldi and the 13 paratypes of O. mimulus) have five branched rays in the pectoral fin, and all 226 specimens examined from the laguna dos Patos basin have six branched rays in the pectoral fin, except for one specimen in UFRGS 4963 and nine juveniles from MCP 15068, with five rays in one or both sides
Aquino (1996) proposed that Otocinclus arnoldi is a junior synonym of Otocinclus flexilis based on overlapping results in morphometric and meristic characters, and the color pattern
Summary
Otocinclus flexilis Cope, 1894 was described from the rio Jacuí, Rio Grande do Sul State, Brazil, based on a syntype series with two lots and 17 specimens, collected by Herbert H. Smith in 1882 and deposited in the Academy of Natural Sciences of Philadelphia under catalog numbers ANSP 2162221626 and ANSP 21756-21767. Cope (1894: 97) diagnosed O. flexilis from O. affinis Steindachner, 1877, mentioning the presence of six branched pectoral-fin rays and describing the color pattern as “light yellowish brown, with a row of about six oblong dusky spots along the lateral line, which become obscure anteriorly. A series of corresponding spots along the dorsal region. Dorsal and caudal fins light colored with numerous dusky spots. A black spot at the base of caudal fin in some specimens”
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