Two new, remarkably colored species of the Neotropical catfish genus Cetopsorhamdia Eigenmann & Fisher, 1916 (Siluriformes, Heptapteridae) from Chapada dos Parecis, western Brazil, with an assessment of the morphological characters bearing on their phylogenetic relationships

Two new species of heptapterid catfish genus Cetopsorhamdia are described from close localities in western Brazil, at Chapada dos Parecis, an area with extremely high level of endemism. One species is from the upper Rio Madeira system, Rondônia State, and the other from the upper Rio Tapajós system, Mato Grosso State. The two species are diagnosed, among several other features, by their markedly distinctive color patterns, with the former having well-defined quadrangular marks in trunk flanks while the latter bearing irregular, vertical bars along the trunk. The monophyly of Cetopsorhamdia is discussed, with two putative synapomorphies being proposed to support the genus. Potentially informative morphological characters to resolve the internal relationships of the genus are presented and discussed. Despite the striking external differences between the two species herein described, they are found to likely form a clade.


INTRODUCTION
One of the most diversified and widely distributed Neotropical catfish families is Heptapteridae, currently totaling 23 valid genera and 228 valid species (Phreatobius Göldi, 1905 has been excluded and assigned to its own family - Sullivan et al., 2013;Lundberg et al., 2014). Heptapterids inhabit freshwater water bodies draining into the Atlantic Ocean from northern Mexico to southern Argentina and to the Pacific Ocean from northern Mexico to southern Peru (Bockmann & Guazzelli, 2003;Bockmann & Ferraris-Jr., 2005;Fricke et al., 2021). Fishes of this family are generally small to medium-sized and prefer small rivers with shallow, fast waters although there are forms living in deep channels of large rivers and in calm waters inside caves (Heptapteridae bears the second largest diversity of troglomorphic fishes in the Neotropics) (Bockmann & Guazzelli, 2003;Bockmann & Castro, 2010).
Based on the phylogenetic analysis of the family performed by Bockmann (1998), a stricter definition of the genus Cetopsorhamdia has been proposed. Consequently, several of these species must have been assigned to different genera of Heptapteridae, some yet to be described (cf. Bockmann, 1998;Zuanon et al., 2006;Bockmann & Slobodian, 2018). Therefore, five nominal species are currently recognized as belonging to Cetopsorhamdia: C. boquillae, C. iheringi, C. insidiosa, C. nasus, and C. picklei. As is the case for the whole family Heptapteridae (Bockmann, 1998;Bockmann & Guazzelli, 2003), the alpha diversity of Cetopsorhamdia is considerably underestimated, containing at least eight species pending description, some of which have already been listed in catalogs and faunistic works (cf. Ohara & Lima, 2015;Ohara & Loeb, 2016;Ohara & Marinho, 2016;. During the Brazilian leg of the Transcontinental Catfish Expedition, funded by the All Catfish Species Inventory Project, carried out mainly across the upper Paraguay, upper Tapajós, upper and middle Madeira and Purus, at least 38 new catfishes have been unveiled (Reis, 2005). About one-third of all new species are heptapterids and, among them, there were two beautifully colored species that were putatively assigned to Cetopsorhamdia. Furthermore, in the last 15 years, collections carried out by the teams of the ichthyology laboratories of the Federal University of Rondônia and Museu de Zoologia da Universidade de São Paulo have brought to light additional material of these two species. In order to help fill the taxonomic gap of the family Heptapteridae (Dubois, 2010;Raposo et al., 2020) and, in particular, of the genus Cetopsorhamdia, in this work we describe these two new forms. As a basis for the observations made, comments on potentially informative morphological characters are presented to diagnose the genus and elucidate its internal relationships.

MATERIAL AND METHODS
Measurements and counts were made on the left side of specimen whenever possible. All measurements were taken point-to-point with digital calipers and expressed to the nearest 0.1 mm. Methodology and terminology for measurements followed Bockmann & de Pinna (2004) and Bockmann & Castro (2010), excluding the nasal barbel length which is inapplicable due to the absence of that structure. Subunits of the head were presented as proportions of head length (HL), except for measurements of barbels, which were converted to proportions of standard length (SL). Head length and measurements of trunk parts were given as proportions of SL.
Methodology and terminology for taking meristic data and fin position followed Bockmann & de Pinna (2004) and Bockmann & Castro (2010). All anal-fin rays were counted individually, including the anterior splints and the two most posterior rays inserted in the same base. When a ray is distally broken or ill-formed, this element is counted and its branching pattern is, whenever possible, presumed according to the adjacent rays. Vertebral counts encompassed all vertebrae, including the first five modified into the complex vertebrae and the compound caudal centrum (PU1+U1) counted as a single element -cf. Lundberg & Baskin (1969). Counts of serial elements (branchiostegal rays, basal radials, pleural ribs, rays associated to caudal skeleton, procurrent rays, and vertebrae), and records of the first vertebra bearing a complete hemal spine and of fin positions (in relation to vertebral number) were taken from cleared and stained preparations and radiographs. The landmarks of the fin origin and terminus are always the total vertebrae (i.e., the first five vertebrae associated with the Weberian complex are considered). Numbers of fin rays and branchiostegal rays were also verified in alcohol-preserved specimens with aid of transmitted illumination. In the descriptions, holotype counts are followed by an asterisk.
Cleared and counterstained specimens were prepared according to Taylor & Van Dyke (1985). Radiographs were obtained at FMNH, LIRP, MZUSP, and USNM (see list of institutional acronyms below). Most radiographs were obtained using a digital radiography cabinet-x-ray equipment Faxitron, model LX-60-DC12, hosted at the Laboratório de Ictiologia de Ribeirão Preto (LIRP), belonging to the Center for Biodiversity Documentation, Department of Biology, FFCLRP/University of São Paulo, Ribeirão Preto, SP, Brazil. All radiographs were stored at

Diagnosis
Cetopsorhamdia clathrata differs from its congeners, and all other heptapterids, by a unique color pattern of trunk constituted by two longitudinal rows of 10-12 quadrangular marks which gives the fish a crisscross appearance (evident in specimens 27.8 mm SL and larger). Such a color pattern is produced by two presumably independent features: 9-11 transverse bars of interrupted pigmentation and an unpigmented stripe along the midlateral portion of trunk (vs. body homogeneously darkly pigmented or with different color pattern). Specimens of all sizes of C. clathrata are further distinguished from      40-42, usually 41 (vs. 37 in C. boquillae; 37-39, usually 37-38, in C. iheringi; 35-38, usually 36-37 in C. insidiosa, C. nasus, and C. picklei; 39-40 in C. spilopleura). It can be distinguished from most species of Cetopsorhamdia, except C. spilopleura, by having: very short maxillary barbel, not reaching posterior margin of opercle in specimens 22.4 mm SL or longer (vs. reaching the first third of pectoral fin in C. insidosa and C. nasus; reaching the second third of pectoral fin in C. iheringi and C. picklei; and surpassing the posterior margin of pectoral fin in C. boquillae); dorsal fin more posteriorly located, with first basal radial articulated with the bifid dorsal process of vertebrae 11-12 (vs. 8-9 in C. boquillae, C. iheringi, C. insidiosa, C. nasus, and C. picklei); anal fin situated more posteriorly, with its first basal radial normally articulated between hemal spines of vertebrae 23-25 (vs. 21-22 in C. boquillae and C. insidiosa, 21-23 in C. iheringi and C. nasus; and 20-23, usually 20-22, in C. picklei); and whitish ovoid areas on both caudal-fin lobes (vs. caudal fin lobes homogeneously dark in other species). Cetopsorhamdia clathrata is further distinguished from C. spilopleura by having fins narrow, with marked concave posterior margins (vs. fins broad, with convex posterior profiles); a long and complete lateral line, extending to slightly beyond the caudal-fin base (vs. lateral line fragmented as isolated patches behind the level of the adipose-fin origin, reaching the level of the anterior portion of the caudal plate); and the laterodorsal and lateroventral regions of the trunk with continuous dark pigmentation (not forming two unpigmented lateral streaks), except for the intervals between the squares (vs. laterodorsal and lateroventral regions of trunk devoid of dark pigmentation).

Description
Morphometrics of holotype and some paratypes in Table 1. See Figs. 1-4 for general body shape. Body relatively elongated, its cross-section oval predorsally, becoming gradually more compressed caudally. Anterior dorsal profile of body gently convex, with sometimes discrete hump at posterior limit of head. Dorsal profile of head gently convex, continuous with dorsal profile of trunk. Dorsal profile of trunk posterior to dorsal-fin base approximately straight to base of caudal fin. Ventral profile of head approximately straight and continuous with abdominal region. Ventral trunk contour slightly convex or straight from pelvic-fin origin to end of anal-fin base, and straight to base of caudal fin. Posterior body depth gradually decreasing caudally. Axillary pore minute, just dorsal to pectoral-fin base, and ventral to first pore of lateral line. Urogenital and anal openings adjacent to each other; anal opening approximately on vertical through middle of pelvic fin.
Head longer than broad, depressed, and subtriangular to trapezoidal in dorsal view . Anterior and posterior cranial fontanels short, separated from each other by broad bridge, about two times longer than each fontanel (Fig. 6B). Eye small, laterodorsally located, approximately equidistant from snout tip and supraoc-cipital end, and without free orbital rim except for shallow ventral invagination. Deep longitudinal facial ridge marking dorsal limit of adductor mandibulae muscle, extending from dorsal base of maxillary barbel to or just anterior of eye. Cheek distinctly swollen below eye forming groove to maxillary barbel. Anterior intranarial width and posterior intranarial width approximately equal. Anterior and posterior nares far apart from each other; internarial length slightly greater than distance between each pair of nares. Anterior naris surrounded by fleshy tubular flap of integument, with anterior margin slightly raised. Base of anterior nostril shallow, not sunk in conspicuous trench. Posterior naris wide, elliptical, with transversal axis longest. Posterior naris surrounded by low fleshy flap anteriorly, mesially and laterally; posterior margin devoid of flap. Mouth distinctly subinferior; gape gently convex anteriorly, slightly downturned at corners. Skin of lips with fleshy rictal fold at corner of gape. Rictal fold ventrally subtended by submandibular groove that extends anteriorly to point approximately adjacent to third or fourth preoperculomandibular pores (pm3 and pm4, respectively).
Pectoral fin with distal margin straight to slightly convex (Figs. 1-4), with i,7 (2) or i,8 (15*) rays. First pectoral-fin ray with basal third rigid and unsegmented and distal two thirds flexible and segmented (Fig. 9). First pectoral-fin ray slightly shorter than second (first branched) and third (second branched) rays, whose tips project slightly beyond tip of first ray. Pectoral fin lying parallel to main body axis when expanded and slightly directed upwards when adpressed to body.
Pelvic fin wide, with distal border straight to slightly rounded (Figs. 1-3), with i,5 (17*) rays. Origin of pelvic-fin base slightly posterior to vertical through dorsal-fin origin, on vertical through space between insertions of first (unbranched) and second (first branched) dorsal-fin rays (8*), or on vertical through insertion of second (first branched) dorsal-fin ray (9). Inner margins of pelvic-fin bases apart from each other. Tip of adpressed pelvic fin falling at mid distance between pelvic-and anal-fin origins. Lateralmost ray unbranched, completely flexible, segmented, and with tip distinctly falling short of tips of second and third rays (first and second branched rays, respectively). Origin of pelvic fin on vertical through region between centra 13 and 14 (1), on vertical through verte-bral centrum 14 (5), on vertical through region between centra 14 and 15 (7), or on vertical through vertebral centrum 15 (4*).
Adipose fin moderately deep and short, highest approximately at midpoint (Figs. 1-3). Adipose fin merging gradually with back anteriorly, with imprecise origin. Distance from dorsal-fin base to adipose fin approximately twice length of dorsal-fin base. Origin of adipose fin slightly posterior to origin of anal fin, on vertical through insertion of last unbranched anal-fin ray (5), on vertical through insertion of first branched anal-fin ray (9), or second branched anal-fin ray (2*). Posterior limit of adipose fin well-defined, with distinct free, rounded lobe. Vertical through end of adipose-fin base at or slightly posterior to tip of posteriormost anal-fin ray. Origin of adipose fin on vertical through vertebral centrum 26 (5), on vertical through region between centra 26 and 27 (3), on vertical through vertebral centrum 27 (7), or on vertical through region between centra 27 and 28 (2*). End of adipose-fin base on vertical through vertebral centrum 34 (1), on vertical through region between centra 34 and 35 (4), on vertical through vertebral centrum 35 (9*), on vertical through region between centra 35 and 36 (2), or on vertical through centrum 36 (1).

Pigmentation in alcohol and in life
Background body coloration withish pale or yellow. Body pigmented with brown melanophores dorsally and laterally, except for regions described below; ventral region mostly unpigmented except for few scattered melanophores (Figs. 1-4). Head mostly dark-brown dorsally and laterally. Cheeks (except for its anterior portion), ventral portion of opercle, and entire ventral surface of head unpigmented (Figs. 1-4). Anterior border of snout, anterior to anterior nares, with faint, unpigmented area (with milky hue) (Figs. 1, 4). Midportion of snout, between anterior and posterior nares, with faintly unpigmented area, more evident in juveniles (Fig. 4). Region between corner of mouth and cheek unpigmented, with milky tonality (Figs. 1-3). Maxillary barbel with brown melanophores dorsally, mental barbels yellow (Figs. 1-4). Dark stripe along region from base of maxillary barbel to region right posterior to eye (Figs. 1-4). Elongate, roughly rectangular white or yellow band ventral to eye (Figs. 1-3). Posterior portion of head, from posterodorsal region of opercle to posterior limit of branchiostegal membrane, with very dark mark extending ventrally along branchiostegal membrane (Figs. 1-3), reaching level of pectoral-fin base in larger specimens (50.8 mm SL or larger). Area immediately dorsal to terminus of opercular cleft with unpigmented, milky, oval spot ( Figs. 1-4). Posterior border of supraoccipital of 22.1 mm SL or larger specimens with unpigmented (of milky hue), wide-angled "V" streak, extending laterally to about level of eyes (Figs. 1, 4); such unpigmented nuchal mark missing in 20.3 mm SL or smaller specimens and almost unperceivable in 21.5 mm SL specimen (Fig. 4A). Larger individuals with two longitudinal, wide rows (one laterodorsal and one lateroventral) of 10-12 brown, quadrangular marks on flanks, interspersed by 9-11 vertical unpigmented lines or bars and one unpigmented stripe along its midlateral region, giving crisscross appearance (Figs. 1-2, 3D-E, 4D-E). Marks on both sides not perfectly symmetrical, meeting each other in midline dorsally (Figs. 1, 4). Quadrangular marks arranged as follows: three or four anterior to dorsal fin, one approximately below dorsal-fin base, two approximately between dorsal-and adipose-fin bases, three approximately below adipose-fin base, and one or two along caudal peduncle (Figs. 1-2, 3D-E, 4D-E). Trunk of small specimens (21.5 mm SL or smaller specimen) homogeneously brown colored, lacking unpigmented vertical bars (Figs. 3A, 4A), which become progressively more conspicuous in somewhat larger specimens (22.1 mm SL or larger specimen) (Figs. 3B-E, 4B-E). Larger specimens (50.8 mm SL or larger) with anteriormost quadrangular mark divided into two sections by extra vertical, unpigmented bar or lines (Figs. 1-2); also, quadrangular marks on caudal peduncle trend to subdivide in larger specimens, over ontogeny. Dark laterodorsal and lateroventral regions of trunk continuous or separated by narrow, short, unpigmented midlateral streak to adipose-fin origin, in small specimens (21.5 mm SL or smaller) (Fig. 3A); midlateral unpigmented stripe progressively wider and longer, reaching caudal region, over ontogeny (Figs. 3B-E). Anterior border of pseudotympanum wall, above pectoral-fin base, with dark brown, vertical mark (extending ventrally to level of pectoral-fin base); mark progressively darker and more defined in larger specimens (Fig. 3). Lateral wall of pseudotympanum densely pigmented, except for its central region in smaller specimens (21.5 mm SL or smaller), becoming progressive-ly less pigmented in 22.1 mm SL and larger specimens (Fig. 3). Several small (one to half size of eye), rounded, unpigmented areas dispersed all over dorsal surface of trunk, fewer ventral to lateral line, in 27.8 mm SL and larger specimens (Figs. 1, 3-4); 22.4 mm SL and smaller specimens devoid of such unpigmented spots (Figs. 3-4). Middorsal region of trunk with three unpigmented, milky blotches (Figs. 1-4): one predorsal, rounded, and medium-sized mark (equal or slightly larger than eye size) just anterior to dorsal fin and around base of its first ray; one very discreet postdorsal mark just posterior to dorsal-fin base; and one inconspicuous preadipose mark; post-adipose and pre-caudal marks absent. First dorsal-fin ray light but proximal third of remaining rays and base of adipose fin brown. Base of dorsal fin darkly pigmented. Base of pectoral fin dark dorsally. Fin rays brown, fading distally, in larger individuals, with dark pigmentation restricted to their proximal thirds or almost absent, with few dark chromatophores, in smaller specimens; interradial membranes mostly hyaline. Muscular base of pectoral, dorsal, and anal fins dark brown. Caudal peduncle with dark-brown, blackened, vertical mark, extending posteriorly to limit of skin on base of caudal-fin rays and most evident at base of principal rays (Figs. 1-3); peduncular mark more conspicuous in smaller individuals (Fig. 3). Base of caudal fin lobes with large, oval or rounded unpigmented spots, with milky aspect (Figs. 1-3).

Etymology
The specific epithet is from the Latim "clathratus", meaning latticed, screened, or reticulate, in allusion to the network color pattern of its flanks. An adjective.

Geographic distribution and habitat
The species is known from the headwaters of the Rio Ji-Paraná (or Machado) and Rio Roosevelt basins, both belonging to the upper Madeira system, draining the northern slope of the Chapada dos Parecis, near Vilhena, Rondônia State, Brazil (Fig. 10). The body proportions of these two sets of geographically separated samples, both here assigned to C. clathrata, intermingle (Table 1), as well as the other morphological characteristics, such as color and meristic data, so that there is no reason to treat them as distinct species. The Igarapé Piracolina, where the holotype (MCP 36064) and several paratypes (ANSP 188921, MCP 36063, MNRJ 35877) of C. clathrata were caught, is a small river with sandy bottom, interspersed with sections of gravel and pebbles, and rich aquatic vegetation, with clear waters and moderate to strong current (Fig. 11). Similar habitat and environmental conditions have been reported by Ohara & Lima (2015) and Ohara & Marinho (2016) for C. clathrata (identified as Cetopsorhamdia sp. 3; UFRO-I 22918) in a Figure 10. Drainage map of central western Brazil showing the localities of Cetopsorhamdia clathrata (white circle) and C. spilopleura (white squares). "T" indicates type-locality, each symbol may represent more than one lot or locality.  Ohara, Tencatt & Britto, 2016) and Pyrrhulina sp. That tributary was categorized as a "terra-firme igarapé" (= highland creek), with its sampled stretch located at 585 m above sea level, described as being small, 1.5-2.5 m wide and 0.3-1.5 m deep, with clear and swift waters, and bottom composed of sand and dead leaves, with little preserved riparian vegetation and surrounded by large plantation fields (mostly soy and corn) (Ohara & Lima, 2015: fig. 4; Ohara & Marinho, 2016: fig. 4).

Conservation assessment
The extinction risk of Cetopsorhamdia clathrata is preliminarily assessed as high. The species is known from six localities in headwater streams of the upper Rio Ji-Paraná and one in a headwater creek of the Rio Roosevelt, both part of the Madeira Drainage, with an Extension of Occurrence (EOO) calculated by the convex polygon of 696 square kilometers. The area is severely converted and heavily impacted by deforestation, suffering effects from erosion, silting, and increased turbidity, with extensive agriculture of cotton, soybean, and other commodities that heavily rely on herbicides, pesticides, and fertilizers. There are no estimates of population size or population decline, and no rational can be used to determine the number of locations. For these reasons, C. clathrata is tentatively assessed as Near Threatened (NT) approaching Endangered by the criterion B1 (

Diagnosis
Cetopsorhamdia spilopleura differs from its congeners, and all other heptapterids, by having a unique color pattern of trunk constituted by 18-22 irregular, vertical brown bars, sometimes resembling inverted "v", "y" or "x". In addition, it can be separated from other species of Cetopsorhamdia by having: 7 branched pectoral-fin rays (vs. 8 in C. clathrata; 8-9 in C. boquillae; 8-10, usually 9, in C. iheringi, C. nasus, and C. picklei); and lateral line fragmented as isolated patches posterior to vertical through the level of adipose-fin origin, reaching to anterior portion of caudal plate (vs. long and complete lateral line, extending to slightly beyond the caudal-fin base in all other species of Cetopsorhamdia). It is further distinguished from other Cetopsorhamdia, except C. clathrata, by having: very short maxillary barbel, not reaching posterior margin of opercle (vs. reaching the first third of pectoral fin in C. insidosa and C. nasus; reaching the second third of pectoral fin in C. iheringi and C. picklei, and surpassing the posterior margin of pectoral fin in C. boquillae); dorsal fin situated more posteriorly, with first basal radial normally inserted on bifid dorsal process of vertebra 12 (vs. 8-9 in C. boquillae, C. iheringi, C. insidiosa, C. nasus, and C. picklei); a more posteriorly located anal fin, with first basal radial articulated between hemal spines of vertebrae 22-24 (vs. 21-22 in C. boquillae and C. insidiosa, 21-23 in C. iheringi and C. nasus; and 20-23, usually 20-22, in C. picklei); and whitish ovoid areas on both caudal-fin lobes (vs. caudal fin lobes homogeneously dark in other species). Cetopsorhamdia spilopleura differs further from C. clathrata by possessing: fins broad, with convex posterior profiles (vs. fins narrow, with marked concave posterior borders); the midlateral region of trunk darkly pigmented (vs. midlateral region devoid of pigmentation, forming a white stripe along the lateral line); and the laterodorsal and lateroventral regions of trunk devoid of dark pigmentation, forming unpigmented streaks (vs. laterodorsal and lateroventral regions of trunk with continuous dark pigmentation, except for the intervals between the squares). Table 2. See Figs. 12-14 for general body shape. Body relatively elongated, its cross-section round to vertically oval predorsally, becoming gradually more compressed caudally. Anterior dorsal profile of body gently convex, without noticeable hump at end of head. Dorsal profile of head gently convex, almost straight, continuous with dorsal profile of trunk. Dorsal profile of trunk posterior to dorsal-fin base approximately straight with slight el-evation at origin of adipose fin. Ventral profile of head slightly convex and continuous with abdominal region, also slightly convex. Ventral trunk contour nearly straight from end of pelvic-fin base to caudal-fin base. Posterior body depth gradually decreasing caudally. Axillary pore minute, just dorsal to pectoral-fin base, and ventral to first pore of lateral line. Urogenital and anal openings adjacent to each other; anal opening approximately on vertical through middle of pelvic fin.

Morphometrics of holotype and paratypes in
Head longer than broad, depressed, and subtriangular to trapezoidal in dorsal view (Figs. 12-15). Anterior and posterior cranial fontanels short, separated from each other by broad bridge, about two times longer than each fontanel (Fig. 16). Eye small, laterodorsally placed, approximately equidistant from snout tip and supraoccipital posterior end, and without free orbital rim except for shallow ventral invagination. Deep longitudinal facial ridge marking dorsal limit of adductor mandibulae muscle, extending from dorsal base of maxillary barbel to or just anterior of eye. Cheek distinctly swollen ventral to eye, forming groove to maxillary barbel. Anterior intranarial width and posterior intranarial width approximately equal. Anterior and posterior nares far apart from each other; with separation between them slightly greater than distance between each pair of nares. Anterior naris surrounded by fleshy tubular flap of integument, with anterior border slightly raised. Base of anterior nostril shallow, not sunk in conspicuous trench. Posterior naris wide, elliptical, with transversal axis longest. Posterior naris surrounded by low fleshy flap anteriorly, mesially Figure 12. Cetopsorhamdia spilopleura, MZUSP 121503, 47.9 mm SL, holotype; Brazil, Mato Grosso State, Comodoro: unnamed stream affluent of Rio Doze de Outubro, Rio Tapajós basin. and laterally; posterior border devoid of flap. Mouth distinctly subinferior; gape gently convex anteriorly, slightly downturned at corners. Skin of lips with fleshy rictal fold at corner of gape. Rictal fold ventrally subtended by submandibular groove that extends anteriorly to point approximately adjacent to third or fourth preoperculomandibular pores (pm3 and pm4, respectively).
Barbels relatively short and depressed, and progressively tapering distally (Figs. 12-15). Tip of maxillary barbel almost reaching middle of opercle, usually to or short of posterior margin of bone, when adpressed against body. Tips of outer and inner mental barbels extending to or slightly surpassing outer border of branchiostegal membrane. Outer mental barbel longer than inner barbel. Inner and outer mental barbels inserted at approximately same line or origin of outer mental barbel slightly anterior to origin of inner mental barbel.
Pectoral fin with distal margin slightly convex, i,7 (8*) or i,8 (1) rays. First pectoral-fin ray with basal third rigid and unsegmented and distal two thirds flexible and segmented (Fig. 19). First pectoral-fin ray slightly shorter than second (first branched) and third (second branched) rays, whose tips project slightly beyond tip of first ray. Pectoral fin lying parallel to main body axis when expanded and slightly directed upwards when adpressed to body.
Pelvic fin wide, with distal border rounded (Figs. 12-14), i,5 (17*) rays. Origin of pelvic-fin base at or slightly posterior to vertical through dorsal-fin origin, on vertical through origin of first (unbranched) dorsal-fin ray (1), on vertical through space between origins of first (unbranched) and second (first branched) dorsal-fin rays (2*), on vertical through origin of second (first branched) dorsal-fin ray (4), or on vertical through space between origins of second (first branched) and third (second branched) dorsal-fin rays (2). Inner margins of pelvic-fin bases apart from each other. Tip of adpressed pelvic fin falling short of vertical through anal-fin origin. Lateralmost ray unbranched, completely flexible, segmented, and with tip distinctly falling short of tips of second and third rays (first and second branched rays, respectively). Origin of pelvic fin on vertical through vertebral centrum 14 (3*) or on vertical through region between centra 14 and 15 (6).
Adipose fin deep and short, with deepest point on second third of fin (Figs. 12-14). Distance from dorsal-fin base to adipose fin approximately twice length of dorsal-fin base. Origin of adipose fin slightly posterior to vertical through anal-fin origin, on vertical through insertion of first branched anal-fin ray (8), or second branched anal-fin ray (1*). Posterior limit of adipose fin well-defined, with free, conspicuous rounded lobe. Vertical through terminus of adipose-fin base slightly anterior to tip of posteriormost anal-fin ray. Origin of adipose fin on vertical through vertebral centrum 25 (1), on vertical through region between centra 25 and 26 (1), on vertical through vertebral centrum 26 (4*), on vertical through region between centra 26 and 27 (2), or on vertical through vertebral centrum 27 (1). End of adipose-fin base on vertical through region between vertebral centra 33 and 34 (1), on vertical through vertebral centrum 34 (3*), on vertical through region between centra 34 and 35 (1), or on vertical through vertebral centrum 35 (4).

Pigmentation in alcohol and in life
Background body coloration withish pale or yellow. Body pigmented with brown melanophores dorsally and laterally, except for regions described below; lateroventral and ventral regions mostly unpigmented except for few scattered melanophores, slightly more concentrated dorsal to anal fin . Head mostly dark-brown dorsally; lateral and ventral portions of head unpigmented. Anterior border of snout, anterior to each anterior nare, uniformly dark, lacking unpigmented area. Midportion of snout, between anterior and posterior nares, with two small, adjacent unpigmented areas in juveniles (30.5 mm SL or smaller) (Fig. 14). Region between corner of mouth and cheek unpigmented, with milky hue. Maxillary barbel dorsally with light-brown melanophores, mental barbels yellow. Region along base of maxillary barbel to just posterior to eye with dark stripe. Elongate, roughly rectangular white or yellow band ventral to eye , less evident in larger specimens. Dark mark on posterior portion of head, from posterodorsal region of opercle to posterior limit of branchiostegal membrane, extending ventrally along branchiostegal membrane, reaching level of pectoral-fin base in larger specimens; such dark stripe fused with dark mark dorsal to pectoral-fin base . Posterior border of supraoccipital with unpigmented (of milky hue), broad, M-shaped streak, extending laterally towards posterior extremity of opercle . Trunk background bright yellow, with dark-brown to black marks in life and brownish in alcohol . Dorsum mostly covered by dark-brown, marbled pigmentation . Flanks with [18][19][20][21][22]vertical,dark bars,sometimes resembling inverted "v","y",. Anterior border of pseudotympanum wall, dorsal to pectoral-fin base, with dark brown, vertical mark, fusing dorsally with dark stripe across posterior region of opercle and branchiostegal membrane . Lateral wall of pseudotympanum darkly pigmented, without any unpigmented region . Laterodorsal region of trunk with whitish stripe (formed by absence of melanophores), extending posteriorly from level of pectoral-fin base up to approximately level of anal-fin origin (sometimes interrupting vertical bars), demarking midlateral, broad dark band . Middorsal region of trunk with two unpigmented, milky blotches : one predorsal, rounded, small mark (equal or slightly larger than eye size) just anterior to dorsal fin and around base of its first ray; and one diffuse, postdorsal unpigmented mark, just posterior to dorsal-fin base; preadipose, post-adipose, and precaudal white marks absent. Fin rays brown, fading distally, in larger individuals (40.2 mm SL or larger specimens) , and with dark pigmentation restricted to their proximal thirds or almost absent, with few dark chromatophores, in smaller specimens (Fig. 14); interradial membranes mostly hyaline. Muscular base of pectoral, dorsal, and anal fins dark brown . Adipose fin with ventral ⅔ light-brown and dorsal ⅓ translucent . Caudal peduncle with dark-brown, blackened, vertical mark, extending posteriorly to limit of skin on base of caudal-fin rays and most evident at base of principal rays ; peduncular mark more conspicuous in smaller individuals. Base of caudal fin lobes with large, oval or rounded unpigmented spots, with milky appearance (Figs. 12-14), especially notable in life (Fig. 13).

Conservation assessment
The extinction risk of Cetopsorhamdia spilopleura is preliminarily assessed as low. The species is known from three localities very close together, in the headwaters of the Rio Doze de Outubro, a tributary to the Rio Juruena of the Rio Tapajós drainage. The three localities are very close and preclude the estimation of Extension of Occurrence. Instead, the Area of Occupation was estimated as eight square kilometers by the superposition of a 2 × 2 km grid. The three known collecting sites are located on the highway BR-364, and despite the area west of the road being heavily impacted by deforestation and agriculture, most of the Rio Doze de Outubro basin is located east of the road and is protected by the Nambikwara Indigenous Territory. As no specific threats to the species were detected and based on the inferred more widespread presence in the Rio Doze de Outubro basin, C. spilopleura is tentatively categorized as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Sub-Committee, 2019). Additional fish inventories should be conducted in the region in order reveal the real geographic distribution of this species.

Monophyly of Cetopsorhamdia
The genus Cetopsorhamdia is morphologically diagnosed by four synapomorphies (Bockmann, 1998 fig. D) are distinctly conical, almost triangular, when viewed dorsally. The snout of C. clathrata (Figs. 1,4,5B) and C. spilopleura (Figs. 12,14,15B), although also conical, is much more attenuated, bearing ellipsoid contour in dorsal view. Cetopsorhamdia boquillae, in turn, exhibits a snout with an anterior contour characteristically rounded in dorsal view, which is the typical plesiomorphic morphology among heptapterids (cf. Bockmann, 1998). These last two characters should, therefore, be excluded from the list of Cetopsorhamdia synapomorphies. On the other hand, our study allowed us to hypothesize other two putative synapomorphies for the genus Cetopsorhamdia. One of them, the presence of a vertical, dark band at caudal peduncle, on the region of insertion of caudal-fin rays, had already been mentioned by Eigenmann (1916) in the original description of the genus. Eigenmann (1916) described it as "a dark band at base of caudal", considering it characteristic of C. nasus. This condition was explicitly mentioned and illustrated for C. iheringi, C. insidiosa, and C. picklei in their original descriptions (cf. Steindachner, 1915;Schultz, 1944;Schubart & Gomes, 1959). Although this mark cannot be verified in the types of C. boquillae because they are strongly faded, the examination of a photograph of a live specimen provided by Armando Ortega leaves no doubt about its presence in the species. Ruiz-C. & Román-Valencia (2006) also reported this caudal mark for C. boquillae. Cetopsorhamdia clathrata (Figs. 1-3) and C. spilopleura (Figs. 12-14) exhibit a state different from the remaining species of Cetopsorhamdia, in which the mark is smaller, being mostly restricted to the central portion of the caudal peduncle. In C. boquillae, C. iheringi, C. insidiosa, C. nasus, and C. picklei the caudal mark is larger, W-shaped, distinctly extending towards the dorsal and ventral borders of the caudal peduncle.
In the course of this investigation we identified another character in the hyomandibular bone that also seems to corroborate the monophyly of Cetopsorhamdia. All species of the genus, including C. clathrata (Fig. 21A) and C. spilopleura (Fig. 22A), have an oblique keel (HK) at the posterodorsal region of the lateral surface of the hyomandibula. In spite of Ortega-Lara (2012) had not described such a structure in the hyomandibula of C. nasus, it is possible to identify it, albeit faintly, in his photograph of a c&s specimen (cf. Ortega-Lara, 2012: fig. 10).

Putatively informative features to resolve Cetopsorhamdia's internal relationships
Cetopsorhamdia clathrata and C. spilopleura share with C. iheringi, C. insidiosa, C. nasus, and C. picklei two putatively apomorphic characteristics that are absent in C. boquillae. One is the presence of a conspicuous pointed process on the anterior border of hyomandibula (Figs. 21-22, see arrows), as illustrated and described for C. nasus by Ortega-Lara (2012: fig. 10). On the other hand, C. boquillae has the generalized heptapterid hyomandibula, lacking a pointed process at its anterior margin.
In addition, in all Cetopsorhamdia species other than C. boquillae the ventral lobe of the caudal fin is longer than the dorsal lobe (cf. Eigenmann, 1916Eigenmann, , 1922Steindachner, 1915: pl. 12, fig. 7;Schultz, 1944: pl. 2, fig. d;Schubart & Gomes, 1959: fig. 1; Ortega-Lara, 2012: fig. 19). Such a condition, presumably derived, is exhibited by C. clathrata (Figs. 1-3) and C. spilopleura , although the condition is more discrete in the latter species. Eigenmann (1922) imprecisely characterized the condition of ventral caudal-fin lobe of C. boquillae as "probably somewhat the longer" (likely due to the poor state of conservation of its type series). Indeed, the tips of the caudal-fin rays of the holotype and paratypes of C. boquillae are heavily damaged so that it is not possible to ascertain its state. However, the examination of a photograph of a live specimen of C. boquillae by Armando Ortega allowed us to determine the state of its caudal fin as having a dorsal lobe with the same length of the ventral lobe, or slightly longer. The caudal-fin lobes of approximately the same length or the dorsal lobe slightly longer than the ventral one is plesiomorphic for catfishes (Bockmann & Miquelarena, 2008). A long ventral caudal-fin lobe also occurs homoplastically in the genus Phenacorhamdia (cf. Britski, 1993;Bockmann, 1998;DoNascimiento & Milani, 2008).
Despite the striking morphological differences distinguishing Cetopsorhamdia clathrata from C. spilopleura, they share at least seven presumable apomorphies observed in the hyomandibula, in the dorsal and pectoral fins, and in the body coloration, which are suggestive of a sister group relationship between them.
As above commented, Cetopsorhamdia clathrata (Fig. 21, see arrow) and C. spilopleura (Fig. 22, see arrow) share with most of species of Cetopsorhamdia the presence of a conspicuous pointed process on the anterior border of hyomandibula. These two new species exhibit a further elongation in this process that reaches the metapterygoid so that these bones, together with quadrate, forming a large, rounded fenestra in the suspensorium .
In Cetopsorhamdia clathrata and C. spilopleura the degree of ossification of the first (unbranched) dorsaland pectoral-fin rays is quite distinct from the remaining Cetopsorhamdia species. In these species the first rays of the dorsal and pectoral fins are weakly ossified and stiffened only at their basal portions at most. In C. clathrata ( Fig. 9) the range of variation of the length of the rigid part of the first dorsal-fin ray is 4.0-6.9% SL (x = 5.7, SD = 0.7) and of the first pectoral-fin ray is 3.4-6.2% SL (x = 4.6, SD = 0.7) (Table 1), while in C. spilopleura (Fig. 19) is 5.3-6.4% SL (x = 5.8, SD = 0.4) and 4.1-5.1% SL (x = 4.4, SD = 0.3) ( Table 2). In opposition, the basal portion of first, undivided dorsal-and pectoral-fin rays of C. boquillae, C. iheringi (Fig. 23A), C. insidiosa (Fig. 23B), C. nasus, and C. picklei is densely ossified in comparison to its distal segment, forming a somewhat rigid strut of about ⅓ and ½ size of the total length of those elements, respectively. This condition exhibited by most species of Cetopsorhamdia is closer to that present in several successive basal lineages of the family Heptapteridae in which more than half of the proximal portion of the first ray of the dorsal and the pectoral fins is heavily ossified and stiffened, sometimes forming a spine (cf. Bockmann, 1998). Among these last-mentioned species of Cetopsorhamdia, the proportions of the rigid part of the first dorsal-fin ray in SL are 8.2-12.9% SL whereas the proportions of the rigid part of the first pectoral-fin ray are 10.4-13.5% SL. No material of C. nasus was available to be measured, but examination of the photographs and radiographs of its holotype and data provided by Ortega-Lara (2012) indicates that the first rays of the dorsal and pectoral fins are unquestionably rigid, at least for their ⅓ and ½ proximal parts, respectively, resembling the conditions exhibited by C. boquillae, C. iheringi, C. insidiosa, and C. picklei.
At last, most putative synapomorphies clustering together C. clathrata and C. spilopleura into a clade are observed in their color patterns, namely: (1) a dark stripe across the base of maxillary barbel to the region just posterior to the eye (Figs. 1-4, 12-14); (2) a roughly rectangular unpigmented region just ventral to the eye (Figs. 1-4, 12-14); (3)  terior portion of opercle and branchiostegal membrane (12)(13)(14); (4) a dark, vertical bar at the anterior portion of the trunk, dorsal to the pectoral fin (12)(13)(14); and (5) each lobe of caudal fin with one ovoid, unpigmented area, of milky-looking in life, immediately posterior to the dark mark (Figs. 1-3, 12-14). None of the other species of Cetopsorhamdia has any of these characteristics, alternatively possessing a mostly uniform dark coloration in the referred regions, without bands or unpigmented areas.
For Cetopsorhamdia spilopleura, in turn, three putative autapomorphies have been recognized: (1) anterodorsal region of the quadrate, outlining part of the suspensorium fenestra, expanded and turned backwards, broadly articulating with the ventral part of the anterior process of the hyomandibula (Fig. 22); (2) trunk flanks with 18-22 irregular, vertical brown bars, sometimes resembling inverted "v", "y" or "x" ; and (3) trunk with laterodorsal unpigmented stripe, demarking a broad midlateral dark band along the lateral line .

Distribuition and fish endemism at Chapada dos Parecis
Both species described in this paper inhabit headwater creeks of the Chapada dos Parecis, an elevated geomorphological formation with altitudes between 400 and 700 m, drained by tributaries of the Madeira and Tapajós rivers. This region constitutes what Dagosta & de Pinna (2019) called an extreme shield, an area with an extremely high level of endemism where coexisting closely related lineages are rare, the diversity is low, and few taxa broadly distributed in the remaining Amazon basin occur. Further on the two new Cetopsorhamdia species herein described, the following taxa are endemic to the headwaters of the rivers draining the Chapada  Bertaco & Carvalho, 2005a b;Fisch-Muller et al., 2005;Carvalho & Bertaco, 2006;Bertaco & Malabarba, 2007;Lima et al., 2007;Britski & Lima, 2008;Wingert & Malabarba, 2011;Ohara & Lima, 2015;Ohara & Marinho, 2016;Ohara et al., , 2017Zawadzki et al., 2016).