70 (3): 417 – 433 © Senckenberg Gesellschaft für Naturforschung, 2020. 2020 A new miniature species of Priocharax (Teleostei: Characiformes: Characidae) from the Rio Madeira drainage, Brazil, with comments on the adipose fin in characiforms George M. T. Mattox 1, *, Camila S. Souza 2, Mônica Toledo-Piza 3, Ralf Britz 4 & Claudio Oliveira 2 1 Laboratório de Ictiologia de Sorocaba, Departamento de Biologia, Universidade Federal de São Carlos – campus Sorocaba, São Paulo, Brazil — 2 Departamento de Biologia Estrutural e Funcional, Instituto de Biociências, Universidade Estadual Paulista – campus Botucatu, São Paulo, Brazil — 3 Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil — 4 Museum of Zoology, Senckenberg Dresden, A. B. Meyer Building, 01109 Dresden, Germany — * Corresponding author; email: [email protected] Submitted June 5, 2020. Accepted July 24, 2020. Published online at www.senckenberg.de/vertebrate-zoology on August 11, 2020. Published in print on Q3/2020. Editor in charge: Uwe Fritz Abstract A new miniature species of the freshwater fsh genus Priocharax is described from the Rio Jamari, Rio Madeira drainage, Amazon basin. Priocharax varii sp. n. is the fourth species currently recognized in the genus and shares with the other three the presence of a conspicuous larval pectoral fn in adults, a fully toothed maxilla, a triangular pseudotympanum situated anterior to the ffth vertebra and a tiny size com- bined with a translucent body. The new species is diagnosed from congeners in having an adipose fn, a unique feature within Priocharax. Molecular identifcation of the new species and the other valid Priocharax species supports the morphological fndings. A brief discussion on the presence/absence of the adipose fn in Characiformes is provided. Key words Amazon River basin, barcoding, biodiversity, osteology, taxonomy. Introduction Priocharax is a genus originally described by WEITZMAN 30 – 50 conical teeth in somewhat irregular row, upper & VARI (1987) to include two miniature species (sensu jaw (premaxilla and maxilla) with approximately 45 – 90 WEITZMAN & VARI, 1988): Priocharax ariel Weitzman & conical teeth in somewhat irregular row, and adult body Vari and Priocharax pygmaeus Weitzman & Vari. These size of 11 – 17 mm SL, a feature otherwise unknown in species were collected from the upper Río Orinoco in the Characinae and Cynopotaminae (= Characinae) at Venezuela and in the region of Leticia, Río Amazonas that time. Another feature that according to WEITZMAN & Colombia, respectively. The authors proposed the pres- VARI (1987) distinguishes Priocharax from the remain- ence in adults of Priocharax of a peculiar, larval-like, ing characines is the number of i,5 pelvic-fn rays, with rayless pectoral fn as the main character to diagnose the all the remaining members of the subfamily having i,7 genus. They also listed a set of other diagnostic features pelvic-fn rays. to distinguish Priocharax from most New World charac- Based on the presence of numerous conical teeth in ids except those included in the Characinae and Cyno- the upper and lower jaws and on the elongate maxilla, potaminae (= Characinae): dentary with approximately WEITZMAN & VARI (1987) hypothesized that the relation- ISSN 1864-5755 | eISSN 2625-8498 | DOI: 10.26049/VZ70-3-2020-11 417 Mattox, G. M. T. et al.: A new miniature species of Priocharax from the Rio Madeira drainage, Brazil ships of Priocharax would be among the Characinae, from fve specimens cleared and double stained for car- pending further studies. Twenty-fve years later, MATTOX tilage and bone following the protocol of TAYLOR & VAN & TOLEDO-PIZA (2012) carried out a phylogenetic study DYKE (1985). Total vertebral number includes the four ver- of this subfamily and found out that the Characinae as tebrae of the Weberian apparatus as separated elements. previously proposed were not monophyletic. Rather, The compound ural centrum was counted as a single ver- they restricted the Characinae to a small group of seven tebra. The gill-raker at the junction of the ceratobranchial genera (Acanthocharax Eigenmann, Acestrocephalus Ei- and epibranchial is considered as the posteriormost gill- genmann, Charax Scopoli, Cynopotamus Valenciennes, raker on the lower branch of the gill arch. Photographs Galeocharax Fowler, Phenacogaster Eigenmann and were made with a Zeiss Discovery V20 stereomicroscope Roeboides Günther) and transferred the other genera of with a Zeiss Axiocam digital camera attached. Osteologi- more diminutive fshes to the Heterocharacinae (Gna­ cal terminology follows WEITZMAN (1962) except for inner thocharax Fowler, Heterocharax Eigenmann, Hoplocha­ arm of the os suspensorium instead of os suspensorium, rax Géry, Lonchogenys Myers and Priocharax), together and outer arm of the os suspensorium instead of rib of with Gilbertolus Eigenmann and Roestes Günther. Simi- fourth vertebra, following CONWAY & BRITZ (2007), and lar results were obtained by other morphological (i.e. MI- other updates summarized in MATTOX et al. (2014). In RANDE, 2010) and molecular approaches (i.e., OLIVEIRA et the description, the frequency of each count is provided al., 2011). A recent dataset (MIRANDE, 2018) combining in parentheses after the respective count, with the count both sources of information also partially corroborated of the holotype indicated by an asterisk. Information on the results, albeit not including exactly the same taxa, but meristic and morphometric data of Priocharax ariel and none of those studies except that of MATTOX & TOLEDO- P. pygmaeus were taken from WEITZMAN & VARI (1987). PIZA (2012) included Priocharax in their analyses. In the Specimens examined for this study are deposited in the same year, BETANCUR-R et al. (2018) included Priocha­ Coleção de Peixes da Universidade Federal de Ron- rax ariel in a molecular analysis of characiforms based dônia (UFRO-ICT), Instituto Nacional de Pesquisas da on exons and recovered the genus among genera of the Amazônia (INPA), Laboratório de Biologia e Genética de Characinae, but did not discuss this result any further. Peixes, Departamento de Biologia Estrutural e Funcional, Since WEITZMAN & VARI’s (1987) publication, a third Universidade Estadual Paulista, Botucatu (LBP), Museu species of Priocharax was discovered in the Rio Negro: de Zoologia da Universidade de São Paulo (MZUSP), P. nanus Toledo-Piza et al. (2014). Priocharax nanus was and National Museum of Natural History – Smithsonian diagnosed from P. ariel and P. pygmaeus by the unique (USNM). Sampling for this study was authorized by In- presence of i,6 pelvic-fn rays, presence of the claustrum stituto Chico Mendes de Conservação da Biodiversidade and two post-cleithra. Although still a miniature, P. nanus (ICMBio) through permit number SISBIO/MMA 45429. was interpreted as the least ontogenetically truncated species in the genus. Additional specimens of Priocharax were reported in the literature from new localities (e.g., Molecular analysis QUEIROZ et al., 2013; VIEIRA et al., 2016) or collected dur- ing recent expeditions. Upon closer study, samples from Voucher specimens for the molecular study are deposited the Rio Jamari, Rio Madeira drainage, Amazon basin, in the collection of Laboratório de Biologia e Genética Brazil were found to represent a new species, which is de Peixes (LBP), Departamento de Biologia Estrutural e described in this paper. Funcional, Instituto de Biociências, Universidade Estad- ual Paulista, Botucatu, São Paulo, Brazil. This study is in accordance with the National Council for the Control of Animal Experimentation (CONCEA) approved by UNE- Material & Methods SP Ethics Committee on Use of Animals (CEUA), proto- col number 1058. Twenty specimens of Priocharax were included in the analysis: one specimen of P. nanus and six Morphological analysis specimens of P. ariel from the Rio Negro, nine specimens of P. pygmaeus from the Río Amazonas and four speci- Counts and measurements follow FINK & WEITZMAN mens of the new species from the Rio Madeira, described (1974), Weitzman & Vari (1987) and Menezes & Weitz- herein. A single specimen of Acestrocephalus sardina man (1990) and were taken on the left side of each speci- (Characiformes, Characidae, Characinae) was used to root men whenever possible. All measurements other than the trees. Voucher data are summarized in Table 1. standard length (SL) are expressed as percentages of SL, DNA extraction followed IVANOVA et al. (2006), and except for subunits of the head which are expressed as per- partial sequences of the cytochrome c oxidase subunit I centages of head length (HL). Caudal-peduncle depth is (COI) gene were amplifed by polymerase chain reaction also expressed as percentage of caudal-peduncle length. (PCR) with primers FishF1, FishR1 and FishF2, FishR2 Measurements were taken point to point with a precision (WARD et al., 2005) or L6252-Asn, H7271-COXI (MELO of 0.1 mm from digital photographs of specimens taken et al., 2011). PCR amplifcations were performed in a to- under the stereomicroscope. Counts of vertebrae, teeth, tal volume of 12.5 µl that included 1.25 µl of 10X buffer, gill-rakers and procurrent caudal-fn rays were obtained 0.25 μl of MgCl2 (50 mM), 0.2 μl dNTPs (2 mM), 0.5 μl of 418 VERTEBRATE ZOOLOGY — 70 (3) 2020 each primer (5 mM), 0.1 μl of PHT Taq DNA polymerase Paratypes. LBP 28495, 5, 12.5 – 12.7 mm SL, collected with holo- (Phoneutria), 1.0 μl of genomic DNA (200 ng) and 8.7 μl type. MZUSP 125787, 44, 11.8 – 14.0 mm SL (5 c&s, 11.8 – 13.7 mm SL), collected with holotype. UFRO-ICT 027656, 5, 12.2 – 13.3 mm ddH2O. The thermocycling profle consisted of an initial SL, collected with holotype. denaturation (5 min at 94°C), followed by 30 cycles of chain denaturation (40s at 94°C), primer hybridization (30s Diagnosis. Priocharax varii is distinguished from all at 50 – 54°C) and nucleotide extension (1 min at 68°C), and congeners by the presence of an adipose fn (vs adipose a fnal extension (8 min at 68°C). All PCR products were fn absent). Priocharax varii can be further diagnosed checked on 1% agarose gels and then purifed with Ex- from P.