Relationships and description of a new catfish species from Chapada Diamantina, the northernmost record of Trichomycterus s.s. (Siluriformes, Trichomycteridae)

Psammocambeva exhibits the largest geographical distribution amongst the subgenera of Trichomycterus s.s. , with its present northernmost represented by Trichomycterus tete , endemic to the upper Rio de Contas Basin in the Chapada Diamantina Region, north-eastern Brazil. Herein, we describe a new species recently collected in the Chapada Diamantina Region, but in the Rio Paraguaçu Basin, about 100 km north of the area inhabited by T. tete . A molecular phylogeny using one nuclear and two mitochondrial genes (2430 bp) supported the new species as sister to T. tete ; both species are distinguished by colour patterns, morphometric data, relative position of dorsal and anal fins and osteological character states. The clade comprising the new species and T. tete , endemic to the semi-arid Caatinga biogeographical province, is supported as sister to a clade comprising species from the Rio Doce and Rio Paraíba do Sul Basins, in the Atlantic Forest biogeographical province. This study corroborated the Chapada Diamantina Region, a well-known mountainous biodiversity centre, as an important centre of endemism for trichomycterid catfishes.


Introduction
The Trichomycterinae (hereafter trichomycterines) are the most common fish group in South American mountainous regions (Costa 2021).In eastern and north-eastern Brazilian highlands, trichomycterines are represented by the genus Trichomycterus Valenciennes, 1832, which in its strict sense (i.e.Trichomycterus s.s.) is a well-supported clade, which is sister to a clade containing the genera Cambeva Katz, Barbosa, Mattos & Costa, 2018and Scleronema Eigenmann, 1917(Katz et al. 2018).Trichomycterus s.s.includes the type species of the genus, Trichomycterus nigricans Valenciennes, 1832 and others about 80 species, in six subgenera (Costa 2021).Amongst these subgenera, Psammocambeva Costa, 2021, presently including 35 nominal species, exhibits the largest geographical distribution and is the only one occurring in north-eastern Brazil (Costa 2021;Vilardo et al. 2023).Psammocambeva is well-supported in molecular phylogenies, but it is not diagnosable by unique morphological character states, with species positioning being determined mainly by molecular phylogenies, besides the absence of synapomorphic osteological characteristics of other genera and, exceptionally, by the presence of derived osteological characteristics that are shared by groups of species within Psammocambeva (Costa 2021;Costa et al. 2022Costa et al. , 2023)).
The present northernmost record for Psammocambeva, as well as for Trichomycterus s.s., is Trichomycterus tete Barbosa & Costa, 2011, endemic to the Rio de Contas Basin, southern Chapada Diamantina, north-eastern Brazil (Barbosa and Costa 2011).Recently, one of us (CRMF) collected another species of Psammocambeva in the Chapada Diamantina, but in the Rio Paraguaçu Basin, about 100 km north of the area inhabited by T. tete in the Rio de

Materials and methods
Field studies were approved by ICMBio (Instituto Chico Mendes de Conservação da Biodiversidade; permit number: 38553-13) and field methods by the Ethics Committee for Animal Use of Federal University of Rio de Janeiro (permit number: 065/18).Euthanasia, fixation, preparation for morphological studies and conservation followed methods of our previous studies on trichomycterine systematics (e.g.Costa et al. (2023)).In lists of specimens, C&S indicates cleared and stained specimens for osteological analyses and DNA indicates specimens directly fixed and preserved in absolute ethanol.Geographical names followed Portuguese terms used in the region.Specimens were deposited in the Instituto de Biologia, Universidade Federal do Rio de Janeiro (UFRJ).Comparative material is listed in Costa et al. (2022Costa et al. ( , 2023)).Methods to take and express morphometric and meristic data, morphological terminology, selection of described and illustrated osteological structures and sequence of morphological characters used in the species description are according to our previous studies on Psammocambeva (Costa et al. 2022(Costa et al. , 2023)).
Proceedings for DNA extraction, amplification and sequencing, reading and interpretation of sequencing chromatograms and sequences annotation were according to our previous studies on systematics of Psammocambeva (e.g.Costa et al. (2023)).
Primers for PCR reactions for the three genes used in the analysis, the mitochondrial genes cytochrome b (CYTB) and cytochrome c oxidase I (COX1) and the nuclear encoded gene recombination activating 2 (RAG2), were the same used in other studies on Psammocambeva (e.g.Costa et al. (2023)).The concatenated molecular data matrix comprised 2430 bp (COX1 521 bp, CYTB 1088 bp, RAG2 821 bp).Parameters for PCR reactions and thermal profile of PCR protocol were the same used in Costa et al. (2023).The sequencing reaction thermal profile was 35 cycles of 30 s at 95 °C, 30 s at 55 °C and 1.5 min at 73 °C.GenBank accession numbers are provided in Table 1.
Terminal taxa for the phylogenetic analyses comprised the new species and 22 species of Psammocambeva representing all included lineages.Outgroups were four congeners representing other subgenera of Trichomycterus s.s., two species of the clade Cambeva plus Scleronema, the sister group of Trichomycterus s.s., one species of a distantly related trichomycterine genus, two species representing other Trichomycteridae subfamilies and one species of the Nematogenyidae, the sister group of Trichomycteridae.Alignment of individual gene datasets was made with the Clustal W algorithm (Chenna et al. 2003) implemented in MEGA 11 (Tamura et al. 2021).The optimal partition scheme and the best-fit evolutive models (Table 2) were calculated using the Partition-Finder 2.1.1 (Lanfear et al. 2016) software, based on the Corrected Akaike Information Criterion.Bayesian Inference was performed with MrBayes 3.2.7a(Ronquist et al. 2012), using two independent Markov Chain Monte Carlo (MCMC) runs with 5 × 107 generations; sampling frequency of every 1000 generations; Tracer 1.7.2 (Rambaut et al. 2018) for evaluation of convergence of the MCMC chains, attainment of the stationary phase, effective sample size adequacy and determination of the burnin percentage; and 25% burn-in to calculate Bayesian posterior probabilities.Maximum Likelihood (ML) was performed using IQ-TREE 2.2.0 (Minh et al. 2020), with node support estimated through both ultrafast bootstrap (Hoang et al. 2018) and traditional bootstrap (Felsenstein 1985), with 1000 replicates for each one.

Phylogenetic analyses
The phylogenetic analyses generated identical trees (Fig. 1), in which the new species is highly supported as sister to T. tete, the only other species of Trichomycterus endemic to the Chapada Diamantina.

Taxonomic accounts
Trichomycterus (Psammocambeva) diamantinensis sp.nov.Diagnosis.Trichomycterus diamantinensis is distinguished from all other species of Psammocambeva by having a unique colour pattern of adult specimens consisting of a faint brown stripe along the lateral mid-line of trunk, overlapped by a great concentration of rounded light brown spots in a more superficial layer of skin (vs.never a similar colour pattern).Trichomycterus diamantinensis also differs from its hypothesised sister species and the only other species of the CD-clade, T. tete, by having the anal-fin origin at a vertical posterior to the dorsal-fin base (vs.through the posterior portion of the dorsal-fin base), a longer nasal barbel, its tip posteriorly reaching the opercular patch of odontodes (vs.reaching area between the orbit and the opercular patch of odontodes), 39 or 40 vertebrae (vs.36 or 37), a deeper body (body depth 14.0-17.3%SL vs. 12.5-13.2%),a deeper caudal peduncle (caudal peduncle depth 11.5-12.9%SL vs. 9.7-10.8%),a wider body (body width 11.2-12.3%SL vs. 7.3-9.0%),a wider head (head width 83.1-89.3% of head length vs. 68.7-77.5%), the anal-fin origin at a vertical through the centrum of the 25 th vertebra (vs.22 nd or 23 rd vertebra), the sesamoid supraorbital slender, without a lateral process (Fig. 4A; vs. with a lateral expansion, often forming a distinctive process, Fig. 4D), a relatively wider metapterygoid and quadrate (Fig. 4B vs. Fig.4E) and a minute ventral middle foramen of the parurohyal (Fig. 4C; vs. broad, Fig. 4F).
Description.General morphology.Morphometric data are in Table 3. Body moderately slender, head and trunk excluding caudal peduncle with dorsal profiles slightly convex, and ventral profile nearly straight, dorsal and ventral profiles of caudal peduncle approximately straight.Greatest body depth at vertical just anterior to pelvic-fin base.Trunk subcylindrical anteriorly, compressed posteriorly.Anus and urogenital papilla at vertical through dorsal-fin origin or just posterior to it.Head subtrapezoidal in dorsal view, snout profile slightly convex.Eye relatively small, dorsally positioned in head, nearer snout margin than opercle.Posterior nostril located nearer anterior nostril than orbital rim.Tip of maxillary barbel posteriorly reaching between posterior limit of interopercular patch of odontodes and pectoral-fin base, rictal barbel reaching posterior portion of interopercular patch of odontodes and tip of nasal barbel reaching opercular patch of odontodes.Mouth subterminal.Jaw teeth pointed, slightly curved, arranged in irregular rows.Premaxillary teeth 45-50, dentary teeth 44-50.Odontodes conical, elongate; opercular odontodes arranged in irregular transverse rows, interopercular odontodes arranged in irregular longitudinal rows.Opercular odontodes 17-19, interopercular odontodes 38-42.Branchiostegal rays 7.
Dorsal and anal fins subtriangular, anterior and posterior margins slightly convex.Total dorsal-fin rays 12 (iii + II + 7), total anal-fin rays 10 (iii + II + 5); anal-fin origin at vertical just posterior to dorsal-fin base end.Dorsal-fin origin at vertical through centrum of 20 th vertebra; anal-fin origin at vertical through centrum of 25 th vertebra.Pectoral fin subtriangular in dorsal view, posterior margin slightly convex, first pectoral-fin ray terminating in filament, its length about 25% of pectoral-fin length without filament.Total pectoral-fin rays 8 (I + 7).Pelvic fin subtruncate, its posterior extremity not reaching urogenital papilla, at vertical through dorsal-fin origin or immediately posterior to it.Pelvic-fin bases medially in close proximity.Total pelvic-fin rays 5 (I + 4).Caudal fin truncate.Total principal caudal-fin rays 13 (I + 11 + I), total dorsal procurrent rays 17 or 18 (xvi-xvii + I), total ventral procurrent rays 13 or 14 (xii-xiii + I).Latero-sensory system.Supraorbital canal, posterior section of infraorbital canal and postorbital canal continuous.Supraorbital sensory canal with 3 paired pores: s1, adjacent to medial margin of anterior nostril; s3, adjacent and just posterior to medial margin of posterior nostril and s6, at transverse line through posterior half of orbit; s6 pore about equidistant from its symmetrical homologous s6 pore than orbit.Infraorbital sensory canal with 2 segments.Anterior infraorbital canal with 2 pores: i1, at transverse line through anterior nostril and i3, at transverse line just anterior to posterior nostril.Posterior infraorbital canal with two pores: i10, adjacent to ventral margin of orbit and i11, posterior to orbit.Postorbital canal with 2 pores: po1, at vertical line above posterior portion of interopercular patch of odontodes, and po2, at vertical line above posterior portion of opercular patch of odontodes.Lateral line of trunk with 2 pores just posterior to head.
Osteology (Fig. 4A-C).Anterior margin of mesethmoid nearly straight, mesethmoid cornu rod-shaped, tip rounded.Lacrimal oval, its largest length about one third of sesamoid supraorbital length.Sesamoid supraorbital narrow, rod-like, longer than premaxilla largest length.Premaxilla sub-rectangular in dorsal view, slightly tapering laterally.Maxilla boomerang-shaped, slender, slightly shorter than premaxilla, with minute posterior process.Autopalatine sub-rectangular in dorsal view when excluding posterolateral process, its shortest width about half autopalatine length, lateral and medial margins weakly concave.Latero-posterior process of autopalatine triangular, its length about two thirds of autopalatine length excluding anterior cartilage.Metapterygoid subtriangular, deeper than long, with distinctive posterior projection; anterior margin weakly bent, posterior margin slightly sinuous.Quadrate robust, dorsoposterior outgrowth in close proximity to hyomandibular outgrowth.Hyomandibula long, anterior outgrowth with small concavity on dorsal margin.Opercle moderately elongate, opercular odontode patch slender, its depth about half length of dorsal articular facet of hyomandibula; dorsal process of opercle short and blunt.Interopercle long, its longitudinal length about three fourths of hyomandibula longitudinal length.Preopercle compact, without ventral expansion.Parurohyal robust, lateral process relatively elongate, sharply pointed.Parurohyal head well-developed, with minute anterolateral paired process.Middle parurohyal foramen small, its largest length about one fourth of distance between anterior margin of parurohyal and anterior insertion of posterior process.Posterior parurohyal process long, slightly longer than distance between anterior margin of parurohyal and anterior insertion of posterior process.Vertebrae 39 or 40.Ribs 13.Two dorsal hypural plates, corresponding to hypurals 4 + 5 and 3, respectively; single ventral hypural plate corresponding to hypurals 1 and 2 and parhypural.
Colouration in alcohol (Figs 2, 3).Dorsum and flank brownish-grey, lighter ventrally, with faint brown stripe along lateral mid-line of trunk, overlapped by great concentration of rounded light brown spots extending over flank and dorsum in more superficial layer of skin.Dorsum light brown with yellowish-grey with mid-dorsal row of small brown spots between nape and dorsal-fin origin.Dorsal and lateral portions of head brownish-grey with brown spots.Ventral surface of head and trunk white.Jaws and barbels brown.Fins hyaline, with faint brown spots on basal portion of unpaired and pectoral fins.Smallest specimen (27.1 mm SL) with flank pale yellow and narrow black stripe along lateral mid-line, which becomes paler and diffuse and overlapped by brown spots in larger specimens.
Distribution and habitat.Trichomycterus diamantinensis is presently known only from the type locality, the Rio da Bomba, a tributary of the Rio Preto, Rio Santo Antônio drainage, Rio Paraguaçu Basin (Fig. 5).Rio da Bomba at the type locality is a dark-coloured small river, about 15 m wide and about 1 m at deepest places, with dense riparian forest in the river banks (Fig. 6).Specimens of T. diamantinensis were found amongst small and medium-sized loose stones, with diameters ranging from 1 cm to 50 cm, approximately, in shallow (about between 5 and 50 cm) and fast-flowing places, with the presence of mosses, algae and fallen leaves composing the microhabitats.They were collected both in shaded and fully sun-exposed places.
Etymology.The name diamantinensis is an allusion to the occurrence of the new species in the Chapada Diamantina, north-eastern Brazil.

Discussion
The present description of T. diamantinensis expands the distribution of Trichomycterus s.s. about 100 km to north, consisting of the first record of the genus for the Rio Paraguaçu Basin, an important fluvial system of north-eastern Brazil, with a surface area about 54,900 km2.A previous record of the occurrence of Trichomycterus further north in north-eastern Brazil by Sarmento-Soares et al. (2011), in the Rio Itapicuru Basin, was actually due to a misplacement of the species Ituglanis payaya (Sarmento-Soares, Zanata & Martins-Pinheiro, 2011), as discussed by Costa   The colour pattern of adult specimens of T. diamantinensis, comprising dark pigmentation occurring in two layers of the skin, with a faint brown stripe along the lateral midline of the trunk at an internal layer, overlapped by a great concentration of rounded light brown spots at a more external layer (Fig. 2), immediately distinguishes this species from all other congeners of Psammocambeva.In T. tete, its hypothesised sister species, the colour pattern consists of dark pigmentation arranged in a single layer, forming round spots separated by broad interspaces (Barbosa and Costa 2011: fig.1).However, juvenile specimens below about 30 mm SL of both species (Fig. 3), share an identical colour pattern, in which the flank is pale yellow with a narrow black stripe along the longitudinal mid-line, possibly corroborating sister group relationships, since no other species of Psammocambeva has a similar colour pattern in juvenile specimens.In the distantly-related Trichomycterus saquarema Costa, Katz, Vilardo & Amorim, 2022, in addition to a broad black stripe along the lateral mid-line, there is another stripe on the dorsal part of the flank (Costa et al. 2022: fig.14C), thus considered a non-homologous condition.
The sources of the Rio Paraguaçu are located in the Chapada Diamantina, a well-known mountainous biodiversity centre with numerous endemic plants (Giulietti et al. 1997).The present study corroborates the Chapada Diamantina as an important centre of endemism for trichomycterid catfishes.In addition to T. diamantinensis and T. tete, endemic trichomycterids include the whole subfamily Copionodontinae (de Pinna 1992), two species of the trichomycterine genus Ituglanis Costa &Bockmann, 1993 (Campos-Paiva andCosta 2007;Costa et al. 2021) and one species of the sarcoglanidine genus Ammoglanis Costa, 1994(Costa et al. 2020).

Figure 1 .
Figure 1.Bayesian Inference topology calculated using MrBayes 3.2.7afor 33 taxa.The dataset comprised two mitochondrially encoded genes (COI, CYTB) and one nuclear gene (RAG2), with a total of 2430 bp.The numbers above branches indicate Bayesian posterior probabilities from the Bayesian Inference analysis and the ultrafast bootstrap and regular bootstrap values from the Maximum Likelihood analyses, respectively, separated by a bar.Asterisks (*) indicate maximum support values and dashes (-) indicate values below 50.

Figure 6 .
Figure 6.Rio da Bomba at the type locality of Trichomycterus diamantinensis sp.nov.

Table 1 .
Species used in the phylogenetic analyses and respective GenBank accession numbers.

Table 2 .
Best-fitting partition schemes and evolutive models.