Rhyacoglanis beninei, Crispim-Rodrigues & Silva & Shibatta & Kuranaka & Oliveira, 2023

Crispim-Rodrigues, Jefferson Luan, Silva, Gabriel de Souza da Costa e, Shibatta, Oscar Akio, Kuranaka, Mariana & Oliveira, Claudio, 2023, Description and phylogenetic position of a new species of Rhyacoglanis (Siluriformes: Pseudopimelodidae) from the Jamanxim River basin, Neotropical Ichthyology (e 230051) 21 (3) : -

Rhyacoglanis beninei , new species

urn:lsid:zoobank.org:act:66E55031-BDEF-47EA-B578-4F4661A03190

( Figs. 1–4; Tab. 1)

Holotype. MZUSP 127014 , 59.1 mm SL, Brazil, Pará State, córrego Jussara, tributary of Jamanxim River, municipally of Novo Progresso , Tapajós River basin, 07°21’08”S 55°17’45”W, 20 Aug 2022, G. S. C. Silva & T. C. Faria.

Paratypes. All from the same locality of holotype. LBP 25081, 5, 26.7–43.7 mm SL, 22 Sep 2017, A. C. Dias, C. S. Souza, C. Souto, N. Flausino Jr. & R. Devidé. LBP 32145, 8, 22.7–50.2 mm SL, the largest specimen was C&S, MZUEL 23049 , 4 , 29.4–42.6 mm SL, 20 Aug 2022, G. S. C. Silva & T. C. Faria. LBP 32163, 3, 27.0– 47.9 mm SL, 22 Aug 2022, G. S. C. Silva & T. C. Faria .

Diagnosis. Rhyacoglanis beninei can be diagnosed from all congeners by two oblique dorsal dark brown bars on the predorsal region ( Fig. 2) (vs. absent). Additionally, R. beninei is distinguished from some congeners by having a dorsal confluence between the dark subdorsal and subadipose bands in large juveniles and adults (> 28 mm SL) (vs. lack dorsal confluence in R. paranensis , R. annulatus , R. varii , and R. rapppydanielae ); ventral confluence between the dark subadipose and caudal peduncle bands (vs. lack ventral confluence in R. annulatus , R. epiblepsis , R. paranensis , R. seminiger , and R. rapppydanielae ); body without conspicuous dark brown spots (vs. conspicuous dark brown spots in R. epiblepsis and R. rapppydanielae ); complete dark band on caudal peduncle (vs. caudal peduncle-band with a unpigmented central region in R. annulatus ); body with three dark bands (vs. two dark bands in R. seminiger ); a thin dark caudal-fin bands (vs. large caudal-fin bands in R. paranensis and R. epiblepsis ); pectoral-fin spine with anterior serrae distributed along the entire margin (restricted to the proximal half in R. pulcher and R. seminiger ); posterior tip of the post-cleithral process reaching vertical through the base of the dorsal-fin spine (vs. not reaching in R. epiblepsis and R. rapppydanielae ); hypural 5 free of hypural 3 and 4 (vs. hypurals 4 and 5 fused in R. rapppydanielae ); pointed caudal-fin lobes (vs. rounded lobes in R. epiblepsis ).

Description. Morphometric data from Rhyacoglanis beninei is available in Tab. 1. In lateral view, straight profile of body from snout tip to dorsal-fin origin followed by a straight profile from dorsal-fin base to caudal-fin insertion. Body ventral surface slightly convex from snout tip to opercular opening region, straight to slightly concave from head posterior end to anal-fin insertion, and straight-angled upward on caudal peduncle. Head depressed with numerous well-developed unculiferous tubercles. Head dorsal profile in a rounded trapezoidal shape, with most anterior region narrower than posterior region. Wide mouth, larger than distance between posterior nostrils. Posterior nostrils opening wider than anterior nostrils. Thick lips with lateral portion extended posteriorly. Dentigerous plates on premaxilla and dentary. Eyes small, covered by skin. Opercular opening covered by a well-developed membrane. Maxillary barbels reaching first branched pectoral-fin ray base. Inner mental barbel small, not reaching isthmus, and outer mental barbel reaching first pectoral-fin ray base. Head laterosensory system bearing conspicuous pores, including six infraorbital, five supraorbital, nine premaxillaries, one premaxillary-postorbital, and one postorbital.

First dorsal-fin ray forming spine locking mechanism. Second dorsal-fin ray modified in a spine, smooth on anterior margin and serrated on posterior margin. Adiposefin base broad, generally larger than dorsal-fin base. Pectoral and pelvic fins roughly triangular, distal margin larger than base. First pectoral-fin ray as spine with retrorse serrations on anterior and posterior margin ( Fig. 3). Pectoral, pelvic, anal, and adipose fins distal margins round. Caudal fin bifurcated with acute dorsal and ventral lobes. Dorsal-fin rays II,6* (1 C&S, 11 eth); pectoral-fin rays I,6* (1 C&S, 13 eth); pelvic-fin rays i,5* (1 C&S, 13 eth); anal-fin rays iii,5 (2 eth), iv,6 (1 C&S) or iii,6 (5), iii,7* (1); caudal-fin rays i,6,8,i* (1 C&S, 11 eth) or i,5,7,i (1 eth). Dorsal procurrent caudal-fin rays 16 (1 C&S), ventral procurrent caudal-fin rays 12 (1 C&S). Branchiostegal rays 8 (1 C&S). Total vertebrae 33 (1 C&S). Ribs 9 (1 C&S).

Coloration in alcohol. Ground color yellowish to brownish, with three conspicuous dark brown bands on body ( Figs. 1, 2, 5). The first dark band under dorsal fin (subdorsal), the second under adipose fin (subadipose), and the third posterior adipose fin, extending to the caudal-fin base. Subadipose and caudal peduncle bands surrounding body; subdorsal band open in ventral region; all bands with variable connections pattern on lateral side ( Fig. 5) in individuals of different SL, sometimes not present in small juveniles (<28 mm SL – Fig. 5C). Two oblique dark brown bands on predorsal region in dorsal view, each beginning just laterally to parieto-supraoccipital process, continuing towards posterior cleithral process ( Fig. 2). Pectoral and pelvic fins hyaline with middle dark brown stripe and numerous melanophores dispersed. Anal-fin hyaline with middle dark brown stripe and numerous melanophores spread; fin base with dark brown band and first unbranched ray base with clear dot. Caudal fin hyaline, dorsal, and ventral lobes with middle dark brown stripe and numerous melanophores dispersed. Dorsal-fin dark brown with numerous melanophores on hyaline margin. Adipose fin dark brown, clear dot on anterior base portion with numerous melanophores. Head grayish with lighter region on cheek.

Coloration in life. Same as alcohol-preserved specimens, but the light regions brighter, ranging from yellowish to brownish ( Fig. 4C).

Geographical distribution. Rhyacoglanis beninei is known only from the type locality in the Jamanxim River , Tapajós River basin, Brazil ( Fig. 6). The new species was collected in fast-flowing currents of Córrego Jussara, characterized by clear water and the bottom with rocks and gravels ( Fig. 4) .

Etymology. Rhyacoglanis beninei is named in honor of Ricardo Cardoso Benine, Professor at Universidade Estadual Paulista “Júlio de Mesquita Filho”, in recognition of his dedication and remarkable contributions to the knowledge of Neotropical freshwater fishes.

Conservation status. All specimens of Rhyacoglanis beninei were collected at only one sample site. However, several specimens were collected at the type locality, indicating a common occurrence and no apparent threat of extinction. According to the International Union for Conservation of Nature ( IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2023), we propose classifying Rhyacoglanis beninei as category Least Concern ( LC).

Phylogeny. Sequencing and data filtering yielded a 70% complete matrix with 1082 loci and 385,841 bp. Results support the monophyly of Pseudopimelodidae and the monophyly of Pseudopimelodinae and Batrochoglaninae subfamilies. Inside Pseudopimelodinae, Cruciglanis is the sister to Pseudopimelodus + Rhyacoglanis , as supported by Silva et al. (2021). Internally to Pseudopimelodus , our analysis found P. bufonius sister to P. charus + P. mangurus (Valenciennes, 1835) . Rhyacoglanis also recovered as a monophyletic group, where R. pulcher was recovered as sister to a clade composed of two subclades, the first composed of R. semininger + R. paranensis and the second composed of R. beninei + Rhyacoglanis n. sp. “Xingu” ( Fig. 7).