Rhyacoglanis varii, Shibatta & Souza-Shibatta, 2023

Shibatta, Oscar Akio & Souza-Shibatta, Lenice, 2023, New species of Rhyacoglanis (Siluriformes: Pseudopimelodidae) from the upper rio Tocantins basin, Neotropical Ichthyology (e 220075) 21 (1) : -

Rhyacoglanis varii , new species

urn:lsid:zoobank.org:act:2A1AD513-0AB2-4D10-91AA-9C3F865A7152

( Figs. 1–3; Tab. 1)

Rhyacoglanis sp. ―Abrahão et al., 2018:3 [brain gross morphology].

Holotype. MZUEL 22317 , 67.1 mm SL, Brazil, Goiás, upper rio Tocantins basin, rio do Peixe, Goianésia , 15 o 28’23.8”S 49 o 13’28.9”W, 14 Jul 2010, O. A. Shibatta, E. Santana, A. Claro-García & L. R. Jarduli.

Paratypes (20 specimens). MZUEL 6039 , 29.6 ‒ 69.1 (10 eth, 5 C&S; 4 COI) , 25.6‒69.1 mm SL, same data as the holotype . MZUSP 54082 , 5 eth, 37.0‒ 47.6 mm SL, Brazil, Goiás, rio Tocantinzinho and tributaries, Serra da Mesa region, Minaçu , 14 o 12’32.02”S 48 o 04’15.17”W, 28 Oct to 4 Nov 1996 , MZUSP / MNRJ staff.

Diagnosis. Rhyacoglanis varii is easily distinguished from congeners (except for R. pulcher ) by the color pattern, with the dark brown vertical bar below the dorsal-fin base not confluent with a dark brown bar below the adipose-fin base (vs. broadly confluent in R. seminiger ), the subdorsal dark brown bar becomes abruptly thinner ventrally (vs. broader in R. paranensis ), dark brown spots sparsely distributed on the body (vs. dense in R. epiblepsis and R. rapppydanielae ), and a solid dark brown bar on caudal peduncle (vs. becoming light brown inside, resembling a circle, in R. annulatus ). Rhyacoglanis varii has the 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. rappydanielae ). Rhyacoglanis varii differs from R. paranensis by the longer distance of anus to anal-fin origin (mean = 11.4±0.8% vs. 10.0±1.4% SL), maxillary barbel length (mean = 79.6±5.8% vs. 74.8±8.7% SL), and caudal peduncle depth (mean = 9.5±0.5% vs. 8.8±0.5% SL); minor posterior nostril to eye distance (mean = 4.8±0.9% vs. 6.7±1.3% SL), body depth (mean = 18.2±1.5% vs. 21.4±2.6% SL), and postcleithral process length (mean = 12.9±1.1% vs. 13.9±1.2% SL). Rhyacoglanis varii differs from R. pulcher and R. seminiger by the shape of the pectoral-fin spine, with anterior serrae distributed along the entire margin (vs. restricted to the proximal half).

Description. Body proportions are given in Tab. 1. Body depressed from snout tip to dorsal-fin origin; progressively compressed from that point to caudal-fin base. Dorsal profile of head and anterior body scarcely convex from snout tip to dorsal-fin origin, then nearly straight, scarcely descending to adipose-fin origin. Ventral head convex, then almost straight from pectoral-fin origin to posterior limit of anal-fin base. Caudal peduncle profile slightly concave along dorsal and ventral margins. Head depressed; slightly longer than wide; anterior margin convex (semicircular) in dorsal view. Head with weakly developed unculiferous tubercles scattered laterally and dorsally. Mouth terminal and wide; width more than one-half of head length (HL). Upper jaw slightly longer than, or same length as, lower jaw. Lips thick and well developed, more so proximate to rictus. Premaxillary tooth plate posterolaterally pointed. Anterior nostril immediately posterior to vertical through rictus. Eye small, superior, covered by skin, slightly posterior to anterior one-third of HL. Opercular membrane well developed; margin falling short of pectoral-fin origin. Maxillary barbel base enlarged. Tip of adpressed maxillary barbel falling short of opercular margin. Adpressed inner mental barbel tip surpassing outer mental barbel base but falling short of its tip. Adpressed outer mental barbel tip reaching opercular membrane margin. Dorsal-fin trapezoidal, distal margin rounded, and first branched ray longer than dorsal-fin base. Dorsal-fin origin immediately posterior to anterior one-third of body but anterior to one-half of SL. Adpressed dorsal-fin tip reaching slightly beyond midpoint between dorsal-fin base terminus and adipose-fin origin. First dorsal-fin ray (spinelet) small, rigid, forming dorsal-fin spine-locking mechanism. Second dorsal-fin ray forming strong, rigid, pointed spine; anterior margin smooth, posterior margin with retrorse serrations. Dorsal-fin rays II,6* (5 C&S, 16 eth). Adipose fin long; base longer than anal-fin base; posterior margin free and rounded. Pectoral-fin margin somewhat triangular, posterior margin rounded. Adpressed pectoral fin tip falling short pelvic-fin origin. First pectoral-fin ray forming strong, rigid, pointed spine, serrated along anterior and posterior margins; posterior serrae retrorse, distinctly larger than anterior serrae (approximately twice as long); pectoral-fin spine notched distally ( Fig. 2). Pectoral-fin rays I,6* (5 C&S, 15 eth), I,5 (1 eth). Pelvic-fin profile almost triangular; posterior margin rounded. Pelvic-fin origin immediately posterior to vertical through dorsal-fin base terminus. Adpressed pelvic fin tip reaching vertical through adipose fin origin. Pelvic-fin rays i,5* (5 C&S, 16

eth). Anal-fin margin rounded; anal-fin rays iii,5 (1 eth), ii,6* (5 eth), iii,6 (9 eth), iv,6 (1 C&S, 1 eth), v,5 (1 C&S), or v,6 (3 C&S). Caudal fin forked; lobes pointed; ventral lobe usually slightly longer than dorsal lobe. Caudal-fin principal rays i,6,5,i (1 eth), i,6,7,i (1 C&S, 1 eth), i,6,8,i* (4 C&S, 13 eth) or i,7,8,i (1 eth). Dorsal procurrent rays 17 (1 C&S), 18 (1 C&S), or 19 (3 C&S); ventral procurrent rays 15 (3 C&S), 16 (1 C&S), or 17 (1 C&S). Skeletal elements supporting the caudal fin as follow: parhypural, hypurals 1 and 2 fused; hypural 3 and 4 fused; hypural 5 free ( Fig. 3). Posterior cleithral process well developed, pointed, tip reaching vertical through anterior dorsal-fin base. Axillary pore present. Lateral line complete. Total vertebrae 33 (2 x-r), 35 (3 C&S), 36 (2 C&S). Ribs 8 (1 X-r), 9 (3 C&S, 1 X-r), 10 (1 C&S), or 11 (1 C&S). Gill rakers 1,0,5* (1 C&S, 5 eth), 1,0,6 (2 C&S, 2 eth), 1,0,7 (6 eth), 1,0,8 (2 eth), 1,1,5 (2 C&S). Branchiostegal rays 7 (1 C&S), 8 (4 C&S).

Head laterosensory canal and pores. Supraorbital(s) canal begins anteromedially to anterior nostril just before vertical through nostril, with five branches (s1, s2, s3, s6 (epiphyseal branch), and s8 (parietal branch)). Infraorbital canal with six branches (i1 to i6), bifurcated anteriorly; i1 lateral to anterior nostril; i2 between anterior and posterior nostrils ( Fig. 4). Preoperculomandibular (pm) canal with ten branches; arched in ventral view; pm1 medio-ventral on head; pm9 at base of opercular bone; canal continuing dorsally, finishing with pm11 fused with first postotic branch (po1). Postotic canal with two branches (po1 and po2), followed posteriorly by trunk lateral-line canal.

Coloration in alcohol. Lateral surfaces of body with yellowish brown ground color. Dorsal surface of head light gray with scattered dark brown specks; pale yellow blotch on adductor muscle region. Maxillary barbel light brown with dark brown specks; mentonian barbel light yellow. Trunk and caudal regions with three dark brown bars. Subdorsal trunk bar approximately triangular, attenuated ventrally, lowermost portion slightly entering belly. Subadipose bar broad, spanning distance between bases of adipose and anal fins, and confluent with contralateral bar, shape roughly rectangular with anterior and posterior margins irregularly concave; rarely in extreme dorsal and ventral contact with dark brown bar on caudal peduncle. Caudal peduncle bar slightly narrower, approximately rectangular, anterior, and posterior margins irregularly concave, dorsally, and ventrally confluent with contralateral bar. Dark brown spots scattered throughout lateral region of body. Ventral region predominantly light yellow, without dark spots. Area between pelvic fins sometimes with tiny spots. Dorsal fin dark brown, distal third with hyaline band; occasionally, band of hyaline elliptical spots on membranes between rays in second lower quarter. Adipose fin with central dark brown vertical band completely separating light yellow spots on anterior and posterior regions, respectively. Pectoral fin hyaline with narrow dark brown band on median region.

Pelvic fin hyaline with irregular or inconspicuous dark brown band across middle of rays. Anal fin hyaline; dark brown, approximately triangular spot near origin, confluent with subadipose band; dark brown oval spots forming irregular band across middle rays. Caudal fin with 3-shaped dark brown band through posterior region; median tip usually confluent with the dark brown bar on caudal peduncle; distal margin hyaline ( Fig. 1).

Coloration in life. Head dorsal region reddish-brown, lateral region with yellowish-

brown spot, peppered with dark brown spots of about pupil size. Maxillary barbel base

light-brown, grayish posteriorly. Eye gray. Trunk and caudal peduncle ground color

light yellowish-brown, with three large black vertical bars (subdorsal, subadipose, and

caudal peduncle), peppered with dark brown spots of eye diameter size. Subdorsal

bar triangular; attenuated ventrally; subadipose bar trapezoidal; caudal peduncle bar

vertically rectangular. Pectoral fin hyaline, reddish-brown, with dark brown band

crossing middle of rays. Dorsal fin about 3/4 black, with distinct reddish-brown distal

margin. Pelvic fin hyaline, reddish-brown, with dark brown spots crossing middle

of rays. Adipose fin black with light brown spots on anterior and posterior regions,

respectively. Anal fin light brown with dark brown band across middle of rays. Caudal

fin hyaline, light brown, with 3-shaped black band on posterior half; distal margin

hyaline ( Fig. 5)

Geographical distribution. Rhyacoglanis varii is known only from the upper rio Tocantins basin on the Brazilian shield ( Fig. 6).

Ecological notes. The type locality in the rio do Peixe presented clear running

waters, mostly shallow, with deeper pools approximately knee height. The bottom is

predominantly pebbles, with rocks, sand, and organic litter ( Figs. 7A,B). The color

pattern of the species, yellowish or orange-brown background with alternating dark

brown bars, allows for perfect camouflage amid the rocks and litter ( Fig. 7C). The area

is in a rural and pristine zone, with marginal vegetation well preserved, which is the

source of the organic litter. Dissolved oxygen 8.3 mg.L- 1, pH 8.06, conductivity 83.4μS.

cm-1, and temperature 22.5° C (at 12:54h Brasília time). Specimens were found under

rocks, protected from the water current ( Fig. 7C), and collected with a sieve with a

high-density polyethylene mesh of 2 mm size as rocks were turned. The use of trawls

or fishing nets was inefficient for their capture.

Etymology. The species name varii honors the ichthyologist Richard P. Vari (1949– 2016) for his outstanding contributions to the systematics of Neotropical fishes.

Conservation status. Considering the criterion established by the IUCN Standards and Petitions Committee ( IUCN, 2022), the species is Data Deficient (DD) because “very little information is known about a taxon, but the available information indicates that the taxon may be threatened”. The species is apparently restricted to the upper Tocantins basin, but the absence of the species in several collections points out its low occurrence in the basin. For instance, in the same expedition when the species was collected, the effort failed to capture it in 18 other localities of Barro Alto, Goianésia, and Pirenópolis municipalities ( OAS, pers. obs.). Furthermore, it is worth mentioning that the rapids environment where the species occurs often lends itself to the construction of hydroelectric plants. Dams entirely alter the river’s flow and seasonality ( Winemiller et al., 2016) and can thereby jeopardize the local population. Also, the dam of the Serra da Mesa power plant may obstruct movement between populations upstream and downstream of the dam.

Multivariate morphometric analysis. Differences in the shape of Rhyacoglanis varii , R. paranensis , and R. rapppydanielae are represented by the second and third axes of the principal components analysis ( Fig. 8). The character loadings, eigenvalues, and percentage of variation are presented in Tab. 2. Rhyacoglanis varii differs from R. paranensis by the longer anus-to-anal-fin origin distance, maxillary barbel length, caudal peduncle depth (positive loadings), and minor posterior nostril-to-eye distance, body depth, and postcleithral process length (negative loadings). Rhyacoglanis rapppydanielae differs from R. varii and R. paranensis by the longer distance between posterior nostril to eye distance, anus to anal-fin origin distance, and mouth width (positive loadings), and by the smaller dorsal-fin spine length and post-cleithral process length (negative loadings).

DNA barcode analysis. The Kimura 2-parameters genetic distance (K2P) between Rhyacoglanis varii and its congeners ranged from 1.9% ( R. paranensis ) to 3.4% ( R. annulatus ), with low intraspecific variation ( Tab. 3). Based on COI gene sequences, species delimitation methods identified 7 MOTUs, corroborating R. varii as a new species. GMYC results indicated seven species with a confidence interval of 5 to 8 species; the maximum likelihood of the null model = 169.5058, the maximum likelihood of the GMYC model = 175.6366, and the threshold time = -0.0034. ABGD analysis resulted in 7 partitions where partition one (maximum previous distance p = 0.001) indicated 7 MOTUs. ASAP analysis retrieved nine partitions, with the lowest scoring partition (2.5) finding 7 MOTUs. The maximum likelihood solution of bPTP delimited 7 MOTUs and suggested a clear separation between the analyzed species. In the Bayesian inference analysis, R. varii was closely related to R. paranensis , and R. annulatus was the sister group of these two species. Rhyacoglanis sp. from the upper rio Araguaia basin ( Fig. 9) was the basal species of the clade and was not closely related to R. varii . All Rhyacoglanis species clustered in a clade with high posterior probability support ( Fig. 10), corroborating the monophyly of the genus. Pseudopimelodus and Cruciglanis were more closely related to each other than to Rhyacoglanis .

Rhyacoglanis varii was recovered from different methods of species delimitation using molecular analysis. The results of those methods are presented as supplementary material: Fig. S1, Neighbor-joining tree; Fig. S2, Number of groups obtained with ABGD method; Fig. S3, Number of groups obtained with ASAP method; Tab. S4, GMYC method, and Fig. S5, Phylogeny of analyzed Pseudopimelodidae species obtained with bPTP method.