New species of Farlowella (Siluriformes: Loricariidae) from the rio Tapajós basin, Pará, Brazil

Abstract A new species of stick-catfish Farlowella is described from streams of the lower rio Tapajós drainage, in Pará State, northern Brazil. The new species is distinguished from all congeners by a naked gular region (vs. gular region with plates) and from most congeners by the presence of five lateral series of plate rows on anterior region of body (vs. four). The new species shows variation in the series of abdominal plates and a discussion on the variation of abdominal plates within Farlowella is made and comments on synapomorphic characters in Farlowellini.


INTRODUCTION
The genus Farlowella Eigenmann & Eigenmann, 1889 is a component of the freshwater fish fauna of the Neotropics.With 32 valid species, Farlowella is the second-most species-rich genus of Loricariinae, a sub-family comprised of 262 valid species in 31 genera (Delgadillo et al., 2021;Londoño-Burbano, Reis, 2021;Fricke et al., 2023).Farlowella representatives are widely distributed in the main cis-Andean South America river drainages and trans-Andean Maracaibo and Magdalena river basins (Terán et al., 2019).They are easily distinguished by having a pronounced rostrum, a thin, elongated, brown body with two longitudinal bands that extend from the tip of the rostrum to the caudal peduncle (Covain, Fisch-Muller, 2007), resembling dry twigs or sticks, which justifies the popular name stick catfishes.
The first taxonomic study was the description of the genus Acestra by Kner (1853), with the first species described: Acestra acus and A. oxyrryncha, but without designating the type species of the genus, until A. acus was determined by Bleeker (1862).However, Acestra was already occupied in Hemiptera (Dallas, 1852) and the name Farlowella was then replaced by Eigenmann, Eigenmann (1889).From the end of the 19 th century, several species were described, totaling 37 names that remained for almost a century, when Retzer, Page (1996) revised the genus based on characters of external morphology.This was the last revision of its species, as well as the first exclusive hypothesis of the phylogenetic relationships of the genus.In that study, the authors performed a phylogenetic analysis with morphological data including only one external group, Aposturisoma myriodon Isbrücker, Britski, Nijssen & Ortega, 1983 (= Farlowella myriodon), that was used to root the tree; the monophyly of the genus, and species relationships were not actually tested.The authors also proposed six species groups and six species were considered as incertae sedis.
Recently, Londoño-Burbano, Reis (2021), based on combined molecular and morphological phylogenetic analysis, formally recognized Aposturisoma myriodon as a member of Farlowella to assign the monophyly of the genus.Although A. myriodon is phenotypically different from Farlowella, this configuration had already been recovered by Covain et al. (2016).Based on the review of Farlowella material deposited in different collections and on the examination of material collected in the river near the confluence with rio Tapajós, in its lower portion, we identified a new species of Farlowella, which is described herein.
Mesethmoid long; lateral expansion of anterior portion absent; mesethmoid ventral posterior process present.Nasal rectangular irregular bone curved laterally.Frontal wide, occluded from dorsal border of orbit.Orbit anteriorly delimited by dermal plate, dorsally by frontal bone, dorsolaterally by sphenotic, and ventrally by infraorbital series.Sphenotic quadrate in shape, contacting frontal bone anterolaterally, parietosupraoccipital dorsally, infraorbital six ventrally, and pterotic-extrascapular posteriorly.Pterotic-extrascapular with large perforations.Parieto-supraoccipital wide and oval, contacting first predorsal plate posteriorly.Anterior contact of hyomandibula with metapterygoid and quadrate, and ventral with preopercle.Symphyseal cartilage between quadrate and hyomandibula.Anterior margin of quadrate articulation with anguloarticular.Dentary almost twice the size of anguloarticular.Autopalatine irregular, rod-like shape.Anterior margin of autopalatine articulation with maxilla and posterior contact posteriorly with vomer and metapterygoid.Preopercle long and partially exposed; anterior process reaching at least half of quadrate length.Suspensorium rectangular in overall shape.Three branchiostegal rays.Hypohyal anterior border Anterior margin of anterohyal greatly expanded.Basibranchial 2, 3 and 4 present; basibranchial 2 and 3 elongated; basibranchial 2 equal to basibranchial 3; basibranchial 2 and 3 ossified and basibranchial 4 cartilaginous.Two hypobranchials; hypobranchial 1 ossified and hypobranchial 2 cartilaginous.Four epibranchials with similar size.Five ceratobranchials; ceratobranchial 1 with accessory flange; ceratobranchial 5 triangular; ceratobranchial teeth restricted to mesial area of plate.Upper pharyngeal plate clubshaped, completely covered with fine teeth.Vertebral count 39(1) and 40(1); five thin pleural ribs directly attached to centra 8, 9, 10, 11 and 12(1) and four thin pleural ribs directly attached to centra 9, 10, 11 and 12(1); parapophysis of complex vertebra well developed (two specimens).New Farlowella species from Tapajós Coloration in alcohol.Ground color of dorsum and head pale or dark brown.Light brown color with diffuse and scattered dark brown spots on predorsal portion, from tip of parieto-supraoccipital and extending to all plates.Five to six rounded spots between the second and third infraorbital, extending to opercle.One dark brown lateral stripe on each side, that runs from snout to caudal peduncle.Ventral portion of head brown; yellow between lower lip and anterior portion of anal fin.Dorsal profile in posterior portion of anal fin light brown with diffuse and scattered dark brown spots along the plates, same to dorsal portion, more delimited in some individuals.Upper lip with scattered chromatophores.Pectoral, dorsal, pelvic, and anal fin rays with hyaline membranes and pigmented brown rays, sometimes forming dark bands.First rays markedly dark.Caudal fin almost completely dark brown, membranes and rays pigmented, in some individuals with area of hyaline membrane (Fig. 4).
Etymology.The specific epithet refers to the combination of the words Wuy jugu, which is the self-denomination of indigenous people known in Brazil as Munduruku.This ethnic group is part of the Tupi trunk and they are located in different regions and territories in the states of Pará, Amazonas, and Mato Grosso.In the region of the lower Tapajós River, in recent years some communities in the process of their ethnic identity have recognized themselves as Munduruku (Ramos, 2022).A noun in apposittion.Variation of abdominal plates within Farlowella wuyjugu.Abdominal plates are usually termed as lateral abdominal plates, which are transversely elongated plates between the pectoral-fin axilla and the pelvic-fin insertion, and midabdominal plates, which cover the abdomen between the lateral ones (Londoño-Burbano, Reis, 2021).The midabdominal plates, in Farlowella, can be absent or present and when present can be incomplete or complete.Ballen et al. (2016b) described Falowella mitoupibo Ballen, Urbano-Bonilla & Zamudio, 2016 and proposed as diagnostic for the species an incomplete median disjunct row of abdominal plates, divided at the center by plates New Farlowella species from Tapajós belonging to the lateral rows of abdominal plates (vs.two or three complete rows of abdominal plates or an incomplete median row of one or two plates anteriorly that never reach to the level of the prepelvic plate).Although the authors proposed this character as a diagnosis for the species, in recent examinations of the type material of F. mitoupibo, it was possible to observe two completes rows of abdominal plates in one specimen (M.Dopazo, pers.obs.).Farlowella wuyjugu have midabdominal plates and can be an incomplete or complete midabdominal series (Fig. 3).An incomplete midabdominal series can be a disjunct row as described for F. mitoupibo or an incomplete median row of plates anteriorly that do not reach to the level of the prepelvic plate (Figs.3A, B).Retzer, Page (1996) proposed the number of rows of abdominal plates as a diagnostic character to differentiate species group of Farlowella: two rows (F.acus (Kner, 1853) group and F. amazonum Günther, 1864 group) and three rows (F.curtirostra Myers, 1942 group, F. mariaelene Martín Salazar, 1964 group, F. nattereri group, F. knerii (Steindachner, 1882) group and unassigned species group).Although Retzer, Page (1996) proposed the number of rows of abdominal plates as a diagnostic character to differentiate species groups of Farlowella, both states were found in F. wuyjugu and F. mitoupibo, rendering that character not be useful to differentiate groups because they are variable within Farlowella species.A phylogenetic analysis of the genus (including the species described here) is being carried out and aims to test if these characters (proposed by Retzer, Page, 1996) are in fact phylogenetically informative.

DISCUSSION
Londoño-Burbano, Reis (2021) recovered the tribe Farlowellini Fowler, 1958 including five genera, Lamontichthys Miranda Ribeiro, 1939, Pterosturisoma Isbrücker & Nijssen, 1978, Sturisoma Swainson, 1838, Sturisomatichthys Isbrücker & Nijssen, 1979and Farlowella Eigenmann & Eigenmann, 1889.The authors defined two exclusive synapomorphies for the tribe: (1) nuchal plate articulated to lateral plates (char 175) and (2) the presence of gular plates (char 179).According to Londoño-Burbano, Reis (2021), gular plates are large, polygonal dermal plates covering the ventral surface of the head behind the lower lip.Character 175 was observed in F. wuyjugu, however, character 179 is not applicable to the new species because of the lack of gular plates.Almost twenty years after the publication of the study by Retzer, Page (1996).Farlowella was proposed as a monophyletic group by Londoño-Burbano, Reis (2021) with 11 morphological and 38 molecular synapomorphies.Of the eleven morphological synapomorphies, four were considered exclusive for the genus: (1) number of branchiostegal rays fewer than four (char 109); (2) straight and upright lamina on neural spine on the sixth vertebra for articulation with ventral surface of parieto-supraoccipital (char 114); (3) absence of pleural rib associated to the seventh vertebra (char 117); (4) short anteriormost paraneural spines (char 129).These character states were all observed in F. wuyjugu supporting the species as a member of the genus.Despite the high number of morphological characters and the number of terminals used in the analysis by the authors, there are many high homoplastic characters and not useful for a diagnosis at the species level.
Other Farlowella species are also identified for the rio Tapajós basin (F.gr.amazonum, F. cf.oxyrryncha, F. schreitmuelleri Arnold, 1936, and F. sp.;M. Dopazo, pers. obs.).Species with type locality in or near the region are F. amazonum (Santarém, Pará State), F. gladiolus Günther, 1864 (rio Cupari, rio Tapajós basin, Amazon River drainage, Pará State), and F. schreitmuelleri (lower Amazon River basin, Santarém, Pará State), but they differ from F. wuyjugu mainly by the number of lateral series of plate rows on anterior region of body (four vs. five).Farlowella amazonum and F. gladiolus were described in the same work by Günther (1864).In the review of the genus by Retzer, Page (1996), F. gladiolus was placed in the synonymy with F. amazonum, however, Covain et al. (2016) recognized the former as a valid species.There are several taxonomic issues regarding the validity of Farlowella species and their delimitation.These questions are being addressed in an ongoing taxonomic review (by MD and MRB) of the genus.Our description of F. wuyjugu contributes to the knowledge of the rio Arapiuns and to the understanding of the ichthyofauna of the rio Tapajós basin.

ETHICAL STATEMENT
Not applicable.

COMPETING INTERESTS
The author declares no competing interests.

FIGURE 1 |
FIGURE 1 | Additional measures used in this study.A. Minimum width of snout; B. Distance between cleithral processes; and C. Maximum width of snout.
Description.Dorsal, lateral, and ventral views of holotype in Fig. 2. Morphometric and meristic data for holotype and paratypes summarized in Tab. 1. Body slender and very elongated, completely covered by dermal plates, except in gular portion.Head triangular and elongate in dorsal and ventral views.Rostrum slender and flat in ventral view.Orbit circular, dorsolaterally placed, visible in dorsal view and not visible in ventral view.Preorbital ridge present.Mouth ventral.Dorsal profile of head concave from snout tip to anterior margin of nares, relatively straight to convex from point to posterior margin of nares to posterior margin of parieto-supraoccipital and slightly concave to dorsal-fin origin.Posterior profile of margin of dorsal-fin origin slightly concave and straight profile to end of caudal peduncle.Ventral profile slightly straight from tip of snout to anal-fin origin, slightly concave in anal-fin base and straight profile to end of caudal peduncle.

TABLE 1 |
Morphometrics of Farlowella wuyjugu, new species.Values as percents of standard length (SL) and head length (HL) for holotype and 38 paratypes.n = number of specimens, SD = Standard deviation.