A new species of Microglanis (Siluriformes: Pseudopimelodidae) from the Pacific slope of Ecuador

A new species of catfish is described from the Esmeraldas River Basin, Pacific slope, northern Ecuador. Tentatively included in Microglanis, represents the second species of the genus inhabiting the Trans-Andean region. The new species is distinguished from known congeners by a unique combination of external characteristics: head and body color pattern, uniform, pale brown, yellowish or grayish, without any kind of blotches, bands or dots, only a lunate transverse band, dark or black, at caudal-fin origin; adipose-fin origin and forward without lighter or luminous areas. Compared with M. variegatus, the new species has morphometric differences, such as the distances between dorsal and pelvic fins, and between posterior nostrils. Some osteological characteristics are compared with those observed in species of Pseudopimelodidae inhabiting the Pacific versant of Colombia and Ecuador and with some other species of Microglanis.


INTRODUCTION
Microglanis Eigenmann, 1912 is the most diverse and geographically widespread genus of family Pseudopimelodidae. Currently, includes 29 described species, all exclusive to South America, that range from Venezuela and Guyana to Argentina, and in the Trans-Andean region of Ecuador, being the SE Brazil the richest area (Ruiz, 2016;Shibatta, 2016;Fricke et al., 2020). Usually, species of the genus inhabit small creeks with crystal clear waters and slow currents, in holes or where submerged leaves, branches, and tree trunks accumulate, with pebbles and stones (Ruiz, 2016).
Diagnostic characteristics for the genus include: small-sized (standard length up to 80 mm); variable color pattern, always includes dark brown blotches, bands, or dots; premaxillary tooth plate without evident projections backward; short or incomplete lateral line (anteriorly, a canal with pores followed posteriorly by free neuromasts, in longitudinal midline); eyes covered by skin; pectoral-fin with five to six branched rays; spines of dorsal and pectoral fins well-developed; and absence of axillary pores (Eigenmann, 1912;Mees, 1974;Shibatta, 2003Shibatta, , 2016Ruiz, Shibatta, 2010;Ruiz, 2016). Some osteological characteristics of the genus include: mesethmoid bifurcated anteriorly; anterior fontanel large, oval-shaped, extends slightly beyond posterior border of eyes; posterior fontanel, on the supraoccipital, circular and small; frontal with lateral margin long and concave, at eyes level; cleithrum with posterior process slender and pointed; mesocoracoid arch filamentous; and gill rakers, elongated and conical (Ruiz, Shibata, 2010;Ruiz, 2016).
Despite the number of described species, there is not a phylogenetic approach for the genus to date. Some species-groups have been described based, only on external morphological characteristics (Ruiz, 2016). Osteological data of the species of Microglanis are scarce, some are provided in the original descriptions of species (Ortega-Lara, Lehmann, 2006;Sarmento-Soares et al., 2006;Mattos et al., 2013). Ruiz (2016) evaluated the diagnostic characters commonly used to identify Microglanis and highlighted the need for osteological studies and phylogenetic analysis to accurately establish genus status and the relationship between species.
During a research project for the study of river ecology and fish diversity at the Pachijal River basin, NW Quito, 18 specimens tentatively identified as a new Microglanis were captured; herein the description of this new species is presented.
Body measurements, meristics and observations on external morphology were made using a stereomicroscope. Measurements were taken on the left side, whenever as possible, point-to-point with a digital caliper with an accuracy of 0.1 mm. Twenty-two morphometric measurements were taken, following Shibatta (2016) and Shibatta, Vari (2017). Measurements are expressed as percentage of standard length (SL) or head length (HL). Meristic data included counts of dorsal, pectoral, pelvic, anal, and caudal-fin rays as well as lateral line pores. The frequency of counts obtained is shown throughout text in parentheses and the asterisk denotes holotype values. Twenty-eight morphometric measurements were taken for the new species and compared with identical measures taken on 12 newly captured specimens of Microglanis variegatus (Tabs. 1-2).

Microglanis berbixae, new species
Description. Morphometric data are summarized in Tab. 1. Small-sized species, maximum size recorded 54.2 mm SL. Body depressed from snout tip to dorsal-fin origin, progressively compressed to caudal-fin base. Highest body depth at dorsal-fin origin and largest body width at pectoral-fin origin. Lateral line short, reach pelvicfin origin, with 8 or 9(*) pores. Contour of ventral surface of head and body almost flat or slightly convex until anal-fin origin, and then slightly concave posteriorly ( Fig.  1). Anus and urogenital papilla are differentiable. Papilla located behind the anus as a thickened fleshy tube, with variable shape between sexes (see "Sexual dimorphism" section).
Head depressed, anteriorly rounded in dorsal view. Eyes small, more dorsal than lateral, closer to mouth than to distal margin of operculum, located near the first third of head length, covered by skin, and without free orbital margin. Snout short. Anterior nostril tubular, closer to upper lip than to eye; posterior nostril near anterior margin of eye, possess an anterior flap (Fig. 1).
Mouth wide, terminal. Teeth villiform, curved backward. Gill membrane free from isthmus, with nine branchiostegal rays. All barbels thin, flattened in cross-section. One maxillary pair, two mental pairs. Maxillary barbel medium-sized, reaching or slightly surpassing pectoral-fin base. Outer mental barbel not reaching pectoral-fin base; inner mental barbel shorter, reaching almost half-length of outer mental barbel (Fig. 1).
Osteological characters. In dorsal and ventral views of mesethmoid, the anterior edge bifurcates and forms conspicuous cornuas (Fig 4). In dorsal view, central area of posterior edge constitutes the anterior margin of anterior cranial fontanelle; laterally, the posterior edge articulates with frontals (Fig. 4A). In ventral view, behind cornuas, bone widens and shows lateral projections smaller than cornuas, with a slightly concave anterior border (Fig. 4B). These projections are visible in both views (Fig. 4). Ventrally, the articulation between mesethmoid and vomer is not visible, both bones are firmly united or fused, cannot be separated. Thus, the presence of a mesethmoidvomer complex is possible (Fig. 4B). In ventral view, the posterior edge shows elongated and pointed middle projection, which is part of the articulation between vomer and parasphenoid (Fig. 4B). Anterior cranial fontanelle is large, oval or elliptical, and nearly 33% of its length is located on the mesethmoid (Fig. 4A).
Parieto-supraoccipital is pentagon-shaped, in dorsal view, articulates anteriorly with frontals, and continues posterior as a process elongated and pointed, not bifurcate. Parieto-supraoccipital articulates anteriorly with sphenotic, in the center with pterotic and posterior with epiotic.
In ventral view, Weberian apparatus (complex centra) shows the transverse processes  of 4th centra, expanded as anterior and posterior projections, with a concave margin at the center, anterior and posterior projections not branched, pointed. Frontal region of anterior projection flat or somewhat deflected ventrally. Transverse processes of 5th centra elongated, curved and pointed (Fig. 5). Thirty vertebrae (six precaudal + 24 caudal). Six pairs of pleural ribs. Branchial apparatus with two basibranchial and two hypobranchial elements ossified, visible. Gill rakers small and conical, first branchial arch with 2, 1, 4-5. Branchiostegal rays, 9.
On pectoral girdle, cleitrum with two projections on distal region, one dorsal, pointed, articulates with posttemporosupracleitrum and a posterior projection (cleithral spine), slender and pointed (Fig. 6A). On dorsal view of escapulo-coracoid bone, filamentous mesocoracoid arch is present (Fig. 6A). Tip of pectoral-fin spine not ossified.  Anterior and posterior surfaces of pectoral-fin spine, dentate. Anterior surface with 10-12 small or weakly developed prickles, on the central and proximal sectors, distal sector without prickles Posterior surface of pectoral-fin spine with 10 prickles welldeveloped (Fig. 6B).

Coloration in alcohol.
Color pattern on specimens preserved in 70% ethanol: head and body color, uniform, pale brown, yellowish or grayish, without bands, dots, blotches, or patches, except transverse lunate band, dark brown, or black at the caudalfin base (Fig. 1). Belly color uniform, pale brown, whitish or grayish, without groups of melanophores. Fins without dots, blotches, or bands; rays with very narrow dark brown or black bands or stripes, proximally and medially. Interradial membrane is hyaline, except on dorsal-fin. Dorsal-fin has dark brown interradial membrane, anterior and proximally, becoming paler or hyaline posterior and distally. Adipose-fin similarly colored as head and body, but the border is hyaline, its origin and forward without lighter or luminous areas. Three specimens with two or three dark brown or black dots, usually horizontally aligned.
Sexual dimorphism. Specimens analyzed have urogenital papilla easily detected behind anus. The papilla is a short tube, thick and fleshy, with cylindrical or triangular shape. Cylindrical-shaped papilla ending truncate with a small pointed flap is associated with females (Fig. 7A). Two of them were dissected, showing well-developed  Scale bars = 1 mm.

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scielo.br/ni | sbi.bio.br/ni ovaries, with yellow ovules visible by the naked eye. Ovaries occupy important volume on posterior region of abdominal cavity. Elongate and triangular papilla, ending in point tip associated with male specimens (Fig. 7B). One dissected male specimen showed developed testicles as ramified bands, white, attached to the dorsal region of abdominal cavity.
Geographical distribution. Specimens were captured in two small rivers of the Pachijal River system, the Sune and Mashpi Rivers (Fig. 8). These rivers belong to the Esmeraldas River Basin, Pacific Ocean versant, northwestern Ecuador, Pichincha province.

Conservation status.
Microglanis berbixae inhabits the Tropical Andes at the Pacific slope of Ecuador. This area belongs to the Tumbes-Chocó-Magdalena hotspot (Myers et al., 2000). The Pachijal River system drains to the Esmeraldas River basin, coastal slope of northwestern Ecuador. In the area, river systems are poorly known and Microglanis berbixae has been reported for only two localities. Consequently, the conservation status of Microglanis berbixae may be classified as Data Deficient (DD), according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN, 2019).

Morphometric comparison.
After comparing the 28 morphometric characteristics between M. berbixae and M. variegatus, only two variables show intervals without overlap: the distance between dorsal and pelvic fins and the distance between posterior nostrils (see Tabs. 1-2).

DISCUSSION
Microglanis berbixae belongs to the family Pseudopimelodidae without any doubt. The external characteristics of the specimens determine this conclusion. However, the generic allocation of the species is controversial, therefore, is included tentatively in the genus Microglanis based on the results of the comparative analyses. First, we compared it with the three species and three genera of Pseudopimelodidae that inhabit the Pacific slope of Colombia and Ecuador (Fricke et al., 2020): Batrochoglanis transmontanus, Cruciglanis pacifici and Microglanis variegatus. Microglanis berbixae has uniform color pattern of head and body, while the color pattern of head and body of the other three species presents spots, bands or dots. The caudal-fin of M. berbixae is truncated, in B. transmontanus and C. pacifici is emarginated, and in M. variegatus the caudal-fin is emarginated or truncated with slightly rounded tips. The lateral line is incomplete and short in all species; in M. berbixae and M. variegatus it only reaches the origin of the pelvic-fin, while in B. transmontanus and C. pacifici, lateral line surpasses the base of the pelvic-fin (Regan, 1913;Eigenmann et al., 1914;Ortega-Lara, Lehmann, 2006). These results indicate that specimens of M. berbixae are more like M. variegatus, but present some significant differences.
When some osteological characters of M. berbixae are compare with those reported for species of Microglanis, B. transmontanus and C. pacifici, the results show: In M. berbixae the vomer is fused with the mesethmoides. Lundberg et al. (1991) Lundberg et al. (1991), but conditions reported in other species of Microglanis indicate that the fusion of mesetmoid and vomer may be variable. In M. berbixae and C. pacifici the distal margin of premaxillary tooth plate is wide and without a posterior projection; in B. transmontanus the distal margin is curved and projecting backwards, while in species of Microglanis the premaxillary tooth plate is rectangular (Ortega-Lara, Lehmann, 2006;Ruiz, 2016;Shibatta, 2016). In M. berbixae and species of Microglanis, the anterior cranial fontanelle is elliptical and wide, while in B. transmontanus is short and narrow, and in C. pacifici is elongated and narrow (Ortega-Lara, Lehmann, 2006;Ruiz, 2016;Shibatta, 2016). In M. berbixae the posterior region or the posterior process of parieto-supraoccipital is elongated and pointed, not forked. A similar condition is indicated for M. iheringi (Ortega-Lara, Lehmann, 2006); but in M. pataxo and M. pleriqueater the posterior process of parieto-supraoccipital is short and bifurcated (Sarmento-Soares et al., 2006;Mattos et al., 2013). Ruiz, Shibatta (2010) point out that a short posterior process on the parieto-supraoccipital is diagnostic for species of Microglanis. At the pectoral girdle, M. berbixae has a filamentous mesocoracoid arch; this condition is diagnostic for the species of Microglanis (Ruiz, Shibatta, 2010;Ruiz, 2016).
The evaluation of the external and osteological characteristics of M. berbixae suggests its inclusion in Microglanis, tentatively, waiting further analyses to determine its appropriate generic status. On the other hand, observed variability on bone components determines the need to improve studies on the osteology to know the variation interval between species of the genus Microglanis.
Among the species included in the genus Microglanis, M. berbixae can be easily recognized. Unlike its congeners, M. berbixae has a uniform body color pattern, making inappropriate the name bumblebee catfish for them, while other species traditionally included in Microglanis have a variable body color pattern, with colored transverse bands or bars and blotches. Shibatta (2014Shibatta ( , 2016 and Ruiz (2016) point out that this color pattern is one of the diagnostic characteristics for Microglanis. Microglanis berbixae and M. variegatus have evident differences in terms of external morphology, but among morphometric variables differences are small and the majority of measurements overlap. A comparative analysis on osteology is ongoing between M. berbixae and M. variegatus, to establish the relationships between them and with other species of Microglanis.
Microglanis berbixae and M. variegatus inhabit the Pacific slope of Ecuador and could be phylogenetically related species. Provenzano, Barriga (2017) provide a similar example with two species of Hemiancistrus that inhabit the same region. Phylogenetic analyses for the species inhabiting the cis-Andean region are required to establish hypotheses of these relationships. These hypotheses and the available knowledge on the geological, climatic or other environmental events (e.g. river capture) could explain the speciation processes that took place in the area, throwing some light to the species diversity and distribution patterns observed nowadays in the Pacific slope of Ecuador.