Science and hobby joining forces for the discovery of three new Corydoras (Siluriformes: Callichthyidae) from the rio Tapajós basin, Brazil, with comments on Corydoras sp. CW111

An expedition crowdfunded by aquarists to a region of the Brazilian state of Pará drained by the Tapajós and Xingu river basins resulted in the capture of five species of Corydoras from the rio Jamanxim basin, a tributary to the rio Tapajós, of which three could be confirmed as new and described herein. The new species can be promptly diagnosed from their congeners by the combination of features related to color pattern and osteology. Considering the gathered information on color patterns and morphology plus field observations, the new species are considered to compose two distinct Müllerian mimicry rings, with two of them forming a mimetic pair, while the third one forms a pair with a fourth nonidentified species captured in the same expedition. An identification key to the species of Corydoras from the rio Tapajós basin is also provided.

However, the number of putative undescribed species recognized by the fishkeeping hobby said to be from this basin is considerably higher, with 20 coded species apparently occurring in the rio Tapajós basin (C86, C133, C145, C146, CW4, CW66, CW101, CW127, CW135, CW146, CW155, CW156, CW162, CW167, CW168, CW170, CW171, CW172, CW173, and CW174; see Tencatt, Evers (2016) for further information on the coding system in Corydoradinae), showing that the diversity of this genus in the rio Tapajós drainage is certainly underestimated. barbel moderate in size, not reaching anteroventral limit of gill opening. Outer mental barbel slightly longer than maxillary barbel. Inner mental barbel fleshy, base of each counterpart slightly separated from each other. Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout and isthmus.
Mesethmoid moderate in size, with anterior tip poorly developed, smaller than 50% of bone length (see Britto, 2003:123, character 1, state 1; fig. 1B); posterior portion wide, partially exposed and bearing small odontodes. Nasal capsule delimited posteriorly and dorsally by frontal, anteriorly by mesethmoid, and ventrally and posteriorly by lateral ethmoid. Nasal relatively wide, laterally curved, inner margin with relatively well-developed laminar expansion contacting frontal and mesethmoid; outer margin with poorly-developed laminar expansion typically contacting lateral ethmoid. Lateral ethmoid moderately expanded anteriorly, with anterodorsal expansion contacting nasal, and anterior margin contacting posterior portion of mesethmoid. Frontal elongated, narrow, width less than half of entire length; anterior projection short, size clearly smaller than nasal length. Frontal fontanel large, slender, and somewhat ellipsoid; posterior tip extension slightly surpassing anterior margin of parieto-supraoccipital. Sphenotic somewhat trapezoid, contacting parieto-supraoccipital dorsally, pteroticextrascapular posteriorly, second infraorbital posteroventrally and frontal anteriorly ( Fig. 2A). Pterotic-extrascapular roughly pipe-shaped, with posteriormost portion contacting first lateral-line ossicle, posteroventral margin contacting cleithrum, and anteroventral margin contacting opercle and variably infraorbital 2; posterior expansion almost entirely covering lateral opening of swimbladder capsule, leaving slender area on its dorsal margin covered only by thick layer of skin. Parieto-supraoccipital wide, posterior process long and contacting nuchal plate; region of contact between posterior process and nuchal plate covered by thick layer of skin.
Two laminar infraorbitals with minute odontodes. Infraorbital 1 conspicuously large, ventral laminar expansion generally strongly well developed; some specimens with well-developed expansion; anterior portion with strongly well-developed laminar expansion, surpassing anterior margin of nasal capsule; inner laminar expansion moderately developed ( Fig. 2A). Infraorbital 2 small, relatively slender, with posterior laminar expansion ranging from moderately to well developed; posteroventral margin contacting posterodorsal ridge of hyomandibula, posterodorsal edge contacting sphenotic and generally pterotic-extrascapular; posterodorsal edge not in contact with pterotic-extrascapular in some specimens; inner laminar expansion ranging from poorly-to moderately developed ( Fig. 2A). Posterodorsal ridge of hyomandibula close to its articulation with opercle relatively slender, exposed, and bearing small odontodes. Dorsal ridge of hyomandibula between pterotic-extrascapular and opercle exposed and bearing odontodes. Interopercle partially covered by thick layer of skin, with posterior portion exposed and bearing odontodes; subtriangular, anterior projection ranging from moderately to well developed. Preopercle elongated, relatively slender; minute odontodes on external surface. Opercle dorsoventrally elongated; relatively compact in shape, with width equal to or slightly larger than half of its entire length; free margin slightly convex, without serrations and covered by small odontodes.
Four branchiostegal rays decreasing in size posteriorly. Hypobranchial 1 deep; hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion well developed, its size 8/40 ni.bio.br | scielo.br/ni Three new Corydoras from the rio Tapajós basin about twice cartilaginous portion. Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with small process on anterior margin of mesial portion; ceratobranchial 3 with continuous laminar expansion on postero-lateral margin; ceratobranchial 5 toothed on posterodorsal surface, with 42 to 45(2) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, with small pointed process on laminar expansion of posterior margin; epibranchial 3 with mesially-curved uncinate process on laminar expansion of posterior margin. Two wide pharyngobranchials (3 and 4); pharyngobranchial 3 with small roughly triangular laminar expansion on posterior margin; rounded expansion in some specimens. Upper tooth plate roughly oval, 48 to 58(2) teeth aligned in two rows on posteroventral surface; rows closely aligned.
Lateral-line canal reaching cephalic laterosensory system through pteroticextrascapular, branching twice before reaching sphenotic: pterotic branch, with single pore, preoperculomandibular branch conspicuously reduced, with single pore opening at postotic main canal; postotic main canal widens just posterior to pterotic branch. Sensory canal continuing through pterotic-extrascapula, reaching sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, other branch connecting to frontal through supraorbital canal, both with single pore. Supraorbital canal branched, running through nasal bone. Epiphyseal branch conspicuously reduced; pore opening close to supraorbital main canal, directed towards frontal fontanel. Nasal canal with three openings, first on posterior edge, second on posterolateral portion and generally fused with first pore, and third on anterior edge. Infraorbital canal running through entire infraorbital 2, extending to infraorbital 1 and opening into two or three pores. Preoperculomandibular branch giving rise to preoperculo-mandibular canal, which runs through entire preopercle with three openings, leading to pores 3, 4, and 5, respectively.
Dorsal fin subtriangular, located just posterior to second or third dorsolateral body plate. Dorsal-fin rays II,8*(20), posterior margin of dorsal-fin spine with 20 to 24 ranging from strongly reduced to poorly-developed serrations; most serrations directed towards tip of spine; some serrations variably perpendicularly directed; serrations absent close to origin of spine; small odontodes on anterior and lateral surfaces of spine (Fig. 2B). Nuchal plate moderately developed, almost entirely exposed, with minute odontodes. Spinelet short; spine typically well developed, with adpressed distal tip surpassing posterior origin of dorsal-fin base. Pectoral fin roughly triangular, its origin just posterior to gill opening. Pectoral-fin rays I,6,i(1), I,7*(3), I,7,i(12), I,8(3) or I,9(1), posterior margin of pectoral spine with 25 to 28 poorly-to moderately-developed serrations along almost its entire length, absent close to origin of spine; most serrations directed towards tip of spine; some serrations perpendicularly directed; small odontodes on anterior, dorsal and ventral surfaces of spine (Fig. 2C). Anteroventral portion of cleithrum exposed; posterolateral portion of scapulocoracoid moderately developed, exposed, with anterior portion slightly expanded anteriorly, not in contact with anteroventral portion of cleithrum; exposed areas bearing small odontodes. Opening of axillary gland sensu Kiehl et al. (2006) located just posterior to pectoral-fin spine base. Pelvic fin oblong, located just below first or second ventrolateral body plate, and at vertical through dorsal-fin spine or first branched dorsal-fin ray. Pelvic-fin rays i,5*(20). Adipose fin roughly triangular, separated from base of last dorsal-fin ray by six or seven dorsolateral body 9/40 ni.bio.br | scielo.br/ni Luiz Fernando C. Tencatt, Willian M. Ohara, Leandro M. Sousa and Marcelo R. Britto plates. Anal fin subtriangular, located just posterior to 12 th or 13 th ventrolateral body plates, and at vertical through adipose-fin spine base or region of preadipose platelets. Anal-fin rays i,4,ii(1), ii,5(16), i,6*(2) or ii,5,i(1). Caudal fin bilobed, with dorsal and ventral lobes similar in size or dorsal lobe slightly larger than ventral lobe. Caudal-fin rays i,11,i(1) or i,12,i*(19), generally four or five dorsal and ventral procurrent rays.
Two laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, both bearing small odontodes. Body plates with minute odontodes scattered over exposed area, with conspicuous line of odontodes confined to posterior margins. Dorsolateral body plates 22(1) or 23*(19). Ventrolateral body plates 20*(17) or 21(3). Dorsolateral body plates along dorsal-fin base 6*(20). Dorsolateral body plates between adipose-and caudal-fin 6(1), 7*(16) or 8(3). Preadipose platelets 2(9) or 3*(11). Ventral surface of trunk between posteroventral margin of cleithrum and pelvic-fin origin laterally delimited only by first ventrolateral body plate; ventral portion of first ventrolateral body plate ranging from slightly to moderately expanded anteriorly. Small platelets covering base of caudal-fin rays. Small platelets disposed dorsally and ventrally between junctions of lateral plates on posterior portion of caudal peduncle. Anterior margin of orbit, above region of junction between frontal and lateral ethmoid, region around nasal capsule, on region above lateral ethmoid, and dorsal, lateral and variably ventrolateral portions of snout with small-to relatively large-sized platelets bearing odontodes; platelets on snout conspicuously more concentrated above mesethmoid. Ventral surface of trunk with numerous small-to relatively large-sized irregular platelets bearing odontodes; region around pectoral-fin origin typically with larger platelets. Vertebral count 21(2); ribs 5(2); first pair conspicuously large, its middle portion closely connected to first ventrolateral body plate; its tip connected to anterior external process of basipterygium. Parapophysis of complex vertebra well developed.

Color in alcohol.
Overall color of body in Fig. 1. Ground color of body paleto brownish yellow or beige. Top of head dark brown; dark area typically extending mesially towards posterior tip of parieto-supraoccipital as thin longitudinal line. Dorsal and lateral surface of head with conspicuous concentrations of dark brown or black chromatophores, forming rounded, irregular or striated, diffuse blotches in some specimens. Lateral surface of cleithrum with conspicuous concentrations of dark brown or black chromatophores, forming rounded, irregular or vermiculated, blotches in some specimens; blotches, when present, diffuse or slightly more marked than blotches on head. Dorsolateral body plates with conspicuous concentration of dark brown or black chromatophores, typically forming rounded, irregular or vertically elongated conspicuous dark blotches; diffuse in some specimens. Ventrolateral body plates, except for region around pelvic-fin origin, with conspicuous concentration of dark brown   Luiz Fernando C. Tencatt, Willian M. Ohara, Leandro M. Sousa and Marcelo R. Britto or black chromatophores, typically forming rounded, irregular or vertically elongated conspicuous dark blotches; diffuse in some specimens; region around pelvic-fin origin with dark brown or black chromatophores but typically not forming any conspicuous pattern; ventral portion of ventrolateral body plates between pelvic-fin origin to area just anterior to anal-fin origin variably with sparse dark brown or black chromatophores. Flank midline variably with distinct longitudinal series of dark brown or black blotches, generally more evident on posterior half of flank. Blotches on flanks ranging from small to moderate in size. Posterior margin of body plates typically with dark brown or black chromatophores, variably forming thin dark lines along border of plates. Dorsal-fin with conspicuous concentrations of dark brown or black chromatophores, forming small dark blotches; blotches roughly longitudinally or obliquely aligned in some specimens, variably fused with each other and forming stripes; some specimens with less evident blotches on posterior portion of fin. Pectoral fin with conspicuous concentrations of dark brown or black chromatophores, forming small, irregular dark spots; spots roughly transversally aligned in some specimens; variably diffuse. Pelvic fin with sparse dark brown or black chromatophores, not forming spots. Adipose fin with dark brown or black chromatophores, generally more numerous and concentrated on spine and on region of membrane close to spine, typically forming single dark patch. Anal fin with conspicuous concentrations of dark brown or black chromatophores, generally more evident along its base, middle portion, and/or posterior portion, forming dark blotches roughly aligned transversally; blotches diffuse and/or not aligned in some specimens. Caudal fin with conspicuous concentrations of dark brown or black chromatophores, mainly on rays, forming dark blotches roughly aligned transversally in three to six slender bars; some specimens with less evident blotches on posterior portion of fin. Color in life. Similar to color pattern of preserved specimens, but with light ground color of body, and with greenish yellow iridescent coloration (Figs. 3-4).

Sexual dimorphism.
As well-documented in Corydoradinae (see Nijssen, Isbrücker, 1980b;Britto, 2003;Spadella et al., 2017), male specimens of C. thanatos present a genital papilla, which is somewhat tubular in shape. Aquarium male specimens eventually display a conspicuous elongation of the first and second dorsal-fin branched rays (Fig.  4B).  Geographical distribution. Corydoras thanatos is currently known from the main channel of the rio Jamanxim and two of its tributaries, both with unknown names, rio Tapajós basin, Novo Progresso Municipality, Pará State, Brazil (Fig. 5).
Ecological notes. The new species was observed to inhabit from main channel of the rio Jamanxim to its small tributary streams (Fig. 6). In the rio Jamanxim, it was mostly associated with the margins of the river, where juvenile specimens were observed shoaling together with juvenile and adult specimens of C. hypnos in the sandy shores, 14/40 ni.bio.br | scielo.br/ni Three new Corydoras from the rio Tapajós basin both species in relatively high abundance. In the small streams, adult and juvenile specimens were found shoaling together with juvenile and adult specimens of C. hypnos, generally in sites with submerged branches, leaf litter, and sandy and/or fine gravel substrate. In these streams, C. thanatos was found in higher numbers than C. hypnos. Although not shoaling together, the new species was found in syntopy with Corydoras sp. CW171 in these streams. In all sampled sites, the new species was mostly observed and captured at night.
Etymology. The specific epithet "thanatos" refers to Thanatos (from the Greek θᾰνᾰτος, thánatos, which means "death"), the Greek god or personification of death, and the twin brother of Hypnos, the god/personification of sleep. The name makes an allusion to the fact that even though both C. thanatos and C. hypnos may present some similarities (in color pattern), they are completely different in other aspects (general morphological pattern). A noun in apposition.

Conservation status.
Corydoras thanatos is currently known from its type locality and two additional records in its surroundings. However, these records are in the border of a conservation unit, the Floresta Nacional do Jamanxim, and no threat to the species as a whole is currently suspected. According to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019), Corydoras thanatos can be classified as Least Concern (LC). Diagnosis. Corydoras hypnos can be distinguished from its congeners, except for the species from the lineages 6, 7 and 9 sensu Alexandrou et al. (2011) plus C. difluviatilis, C. hastatus, and C. pygmaeus, by having posterior margin of pectoral-fin spine with most serrations directed towards the tip of the spine (vs. most serrations directed towards origin of spine); from C. difluviatilis and C. pygmaeus it differs by the presence of contact between nuchal plate and posterior process of the parieto-supraoccipital (vs. absence of contact between nuchal plate and the posterior process of the parieto-supraoccipital); from C. hastatus by the absence of a large-sized dark blotch on caudal-fin base (vs. caudal-fin base region with a dark brown or black large blotch, roughly diamondshaped or rhomboid, or arrow-shaped, typically bordered anteriorly and posteriorly by conspicuously light areas); it can be distinguished from the species within lineage 7 by having dark brown or black markings on fins, except for the pectoral and pelvic fins (vs. fins devoid of conspicuous dark markings); it differs from the species within lineages 6 16/40 ni.bio.br | scielo.br/ni Three new Corydoras from the rio Tapajós basin and 9, except for C. benattii, C. eversi Tencatt & Britto, 2016, C. froehlichi Tencatt, Britto & Pavanelli, 2016, C. granti Tencatt, Lima & Britto, 2019, C. gryphus Tencatt, Britto & Pavanelli, 2014 psamathos, and C. thanatos, by having dorsal surface of snout with numerous platelets bearing odontodes (vs. dorsal surface of snout lacking platelets); from C. benattii and C. froehlichi by having moderately-to relatively well-developed and smoothly rounded snout (vs. conspicuously short and rounded snout); from C. eversi and C. granti, it can be distinguished by having ventral surface of trunk only with smallsized, non-coalescent platelets (vs. ventral surface of trunk entirely or partially covered by moderate-to relatively large-sized, coalescent platelets); from C. gryphus by having midline of flank with longitudinal series of dark brown or black blotches, when present, diffuse (vs. midline of flank with a longitudinal series of four to six conspicuous dark brown or black blotches), and mesethmoid partially exposed (vs. entirely covered by thick layer of skin); from C. psamathos by the presence of conspicuous dark brown or black markings at least in dorsal and caudal fins (vs. absence of conspicuous dark brown or black markings on body; dark markings, when present, diffuse); from C. thanatos by having anterior laminar expansion moderately developed, poorly expanded towards the anteroventral portion of snout, leaving most of its lateral surface exposed (vs. anterior laminar expansion of infraorbital 1 strongly well developed, conspicuously expanded towards the anteroventral portion of snout, significantly covering its lateral surface).
Description. Morphometric data in Tab. 2. Head laterally compressed with convex dorsal profile, roughly triangular in dorsal view. Snout ranging from moderately to relatively well developed and smoothly rounded. Head profile convex from tip of snout to anterior nares; ascending nearly straight or slightly convex from this point to dorsal-fin origin; region of frontal or parieto-supraoccipital slightly concave in some specimens. Profile slightly convex along dorsal-fin base. Postdorsal-fin body profile slightly concave to adipose-fin spine, slightly concave from this point to caudal-fin base. Ventral profile of body nearly straight or slightly convex from isthmus to pectoral girdle, and slightly convex from this point until pelvic girdle. Profile nearly straight or slightly convex from pelvic girdle to base of first anal-fin ray, ascending slightly concave until caudal-fin base. Body roughly elliptical in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin.
Eye rounded, located dorsolaterally on head. Orbit delimited anteriorly by lateral ethmoid, anterodorsally by frontal, posterodorsally by sphenotic, posteroventrally by infraorbital 2, and anteroventrally by infraorbital 1. Anterior and posterior nares close to each other, only separated by flap of skin. Anterior naris tubular. Posterior naris close to anterodorsal margin of orbit, separated from it by distance similar to naris diameter. Mouth small, subterminal, width similar to bony orbit diameter. Maxillary barbel ranging from short to moderate in size, not reaching to anteroventral limit of gill opening. Outer mental barbel slightly longer than maxillary barbel. Inner mental barbel fleshy, base of each counterpart slightly separated from each other. Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout and isthmus.
Mesethmoid moderate in size, with anterior tip poorly developed, slightly smaller than 50% of bone length (see Britto, 2003:123, character 1, state 1; fig. 1B); posterior portion wide, partially exposed and bearing small odontodes. Nasal capsule delimited posteriorly and dorsally by frontal, anteriorly by mesethmoid, and ventrally and posteriorly by lateral ethmoid. Nasal slender, laterally curved, inner margin with poorly-to moderately-developed laminar expansion generally contacting frontal and mesethmoid; variably close but not in direct contact with mesethmoid; outer margin with poorly-developed to strongly reduced laminar expansion. Lateral ethmoid slightly expanded anteriorly, with anterodorsal expansion relatively distant from nasal, and anterior margin contacting posterior portion of mesethmoid. Frontal elongated, narrow, width less than half of entire length; anterior projection short, size smaller than nasal length. Frontal fontanel large, slender, and somewhat ellipsoid; posterior tip extension slightly surpassing anterior margin of parieto-supraoccipital. Sphenotic somewhat trapezoid, contacting parieto-supraoccipital dorsally, pterotic-extrascapular posteriorly, second infraorbital posteroventrally and frontal anteriorly (Fig. 8A). Pterotic-extrascapular roughly pipe-shaped, with posteriormost portion contacting first lateral-line ossicle, posteroventral margin contacting cleithrum, and anteroventral margin contacting opercle; posterior expansion almost entirely covering lateral opening of swimbladder capsule, leaving slender area on its dorsal margin covered only by thick layer of skin. Parieto-supraoccipital wide, posterior process long and contacting nuchal plate; region of contact between posterior process and nuchal plate covered by thick layer of skin.
Two laminar infraorbitals with minute odontodes. Infraorbital 1 large, ventral laminar expansion ranging from poorly to moderately developed; anterior portion with laminar expansion moderately developed, reaching to middle portion of nasal capsule; inner laminar expansion poorly developed (Fig. 8A). Infraorbital 2 small, slender, with posterior laminar expansion ranging from strongly reduced to poorly developed; posteroventral margin contacting posterodorsal ridge of hyomandibula, posterodorsal edge contacting only sphenotic; inner laminar expansion ranging from strongly reduced to poorly developed (Fig. 8A). Posterodorsal ridge of hyomandibula close to its articulation with opercle relatively slender, exposed, and bearing small odontodes. Dorsal ridge of hyomandibula between pterotic-extrascapular and opercle typically covered by thin skin layer. Interopercle entirely covered by thick layer of skin or almost entirely covered by thick layer of skin, with posterior portion exposed, and typically bearing small odontodes; subtriangular, anterior projection moderately developed. Preopercle elongated, relatively slender; minute odontodes on external surface. Opercle dorsoventrally elongated, with width slightly smaller or similar to half of its entire length; free margin slightly convex, without serrations and covered by small odontodes.
Four branchiostegal rays decreasing in size posteriorly. Hypobranchial 1 deep; hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion well developed, its size about twice or triple of cartilaginous portion. Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with small process on anterior margin of mesial portion; ceratobranchial 3 notched on postero-lateral margin; variably with continuous laminar expansion on postero-lateral margin; ceratobranchial 5 toothed on posterodorsal surface, with 34 to 37(3) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, with small pointed process on laminar expansion of posterior margin; epibranchial 3 with mesially-curved uncinate process on laminar expansion of posterior margin. Two wide pharyngobranchials (3 and 4); pharyngobranchial 3 with smoothly rounded to nearly straight laminar expansion on posterior margin. Upper tooth plate roughly oval, 40 to 53(3) teeth aligned in two rows on posteroventral surface; rows closely aligned.
Lateral-line canal reaching cephalic laterosensory system through pteroticextrascapular, branching twice before reaching sphenotic: pterotic branch, with single pore, preoperculomandibular branch conspicuously reduced, with single pore opening at postotic main canal; postotic main canal widens just posterior to pterotic branch. Sensory canal continuing through pterotic-extrascapular, reaching sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, other branch connecting to frontal through supraorbital canal, both with single pore. Supraorbital canal branched, running through nasal bone. Epiphyseal branch conspicuously reduced; pore opening close to supraorbital main canal, directed towards frontal fontanel. Nasal canal with three openings, first on posterior edge, second on posterolateral portion, generally fused with first pore, and third on anterior edge. Infraorbital canal running through entire infraorbital 2, extending to infraorbital 1 and opening into two or three pores. Preoperculomandibular branch giving rise to preoperculo-mandibular canal, which runs through entire preopercle with three openings, leading to pores 3, 4, and 5, respectively; pore 3 variably opening at posterodorsal ridge of hyomandibula.
Dorsal fin subtriangular, located just posterior to second or third dorsolateral body plate. Dorsal-fin rays II,8*(19), II,9(1), posterior margin of dorsal-fin spine with 16 to 17 strongly reduced to poorly-developed serrations; most serrations directed towards tip of spine; some serrations variably perpendicularly directed; serrations absent close to origin of spine; small odontodes on anterior and lateral surfaces of spine (Fig. 8B). Nuchal plate moderately developed, almost entirely exposed, with minute odontodes. Spinelet short; spine moderately developed, with adpressed distal tip slightly surpassing posterior origin of dorsal-fin base. Pectoral fin roughly triangular, its origin just posterior to gill opening. Pectoral-fin rays I,7(3), I,7,i(1) or I,8*(16), posterior margin of pectoral spine with 20 to 32 strongly reduced to moderately-developed serrations along its entire length; most serrations directed towards tip of spine; some serrations perpendicularly directed or directed towards origin of spine; serrations variably bifid; small odontodes on anterior, dorsal and ventral surfaces of spine (Fig. 8C). Anteroventral portion of cleithrum exposed; posterolateral portion of scapulocoracoid moderately developed, exposed, with anterior portion slightly expanded anteriorly, not in contact with anteroventral portion of cleithrum; exposed areas bearing small odontodes. Opening of axillary gland sensu Kiehl et al. (2006) located just posterior to pectoral-fin spine base. Pelvic fin oblong, located just below first or second ventrolateral body plate, and at vertical through first branched dorsal-fin ray. Pelvic-fin rays i,5*(20). Adipose fin roughly triangular, separated from base of last dorsal-fin ray by generally six dorsolateral body plates. Anal fin subtriangular, typically located just posterior to 12 th ventrolateral body plates, and at vertical through adipose-fin spine base or region of preadipose platelets. Anal-fin rays ii,5(19) or ii,6(1). Caudal fin bilobed, with dorsal and ventral lobes similar in size or dorsal lobe slightly larger than ventral lobe. Caudal-fin rays i,12,i*(20), generally four or five dorsal and ventral procurrent rays.
Typically, three laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, both bearing small odontodes; third, encased in third dorsolateral body plates. Body plates with minute odontodes scattered over exposed area, with conspicuous line of odontodes confined to posterior margins. Dorsolateral body plates 23(17) or 24*(3). Ventrolateral body plates 20(13) or 21*(7). Dorsolateral body plates along dorsal-fin base 6*(18) or 7(2). Dorsolateral body plates between adipose-and caudal-fin 7(18) or 8*(2). Preadipose platelets 3*(6) or 4(14). Ventral surface of trunk between posteroventral margin of cleithrum and pelvic-fin origin laterally delimited only by first ventrolateral body plate; ventral portion of first ventrolateral body plate slightly expanded anteriorly. Small platelets covering base of caudal-fin rays. Small platelets disposed dorsally and ventrally between junctions of lateral plates on posterior portion of caudal peduncle. Anterior margin of orbit, above region of junction between frontal and lateral ethmoid, ventral margin of nasal capsule, above lateral ethmoid, and dorsal surface of snout with numerous small-to relatively large-sized platelets bearing odontodes; platelets on anterior margin of orbit and ventral margin of nasal capsule typically larger and 20/40 ni.bio.br | scielo.br/ni Three new Corydoras from the rio Tapajós basin coalescent. Ventral surface of trunk with scarce to relatively numerous small-sized irregular platelets bearing odontodes; platelets more concentrated anteriorly and/or around pectoral-fin base.
Vertebral count 21(3); ribs 5(3); first pair conspicuously large, its middle portion closely connected to first ventrolateral body plate; its tip connected to anterior external process of basipterygium. Parapophysis of complex vertebra well developed.

Low-High Mean±SD
Standard length (

Color in alcohol.
Overall color of body in Fig. 7. Ground color of body paleto brownish yellow or beige. Top of head dark brown; dark area typically extending mesially towards posterior tip of parieto-supraoccipital as thin longitudinal line. Dorsal and lateral surface of head, and lateral surface of cleithrum covered by dark brown or black chromatophores, typically not forming blotches; diffuse stripe from anteroventral portion of eye to upper lip lateral area in some specimens. Dorsolateral body plates with conspicuous concentration of dark brown or black chromatophores, typically forming rounded, irregular or vertically elongated diffuse dark blotches. Ventrolateral body plates, except for ventral portion of plates between pelvic-fin origin to area just anterior to anal-fin origin, with conspicuous concentration of dark brown or black chromatophores, typically forming rounded, irregular or vertically elongated diffuse dark blotches; ventral portion of plates between pelvic-fin origin to area just anterior to anal-fin origin, especially around pelvic-fin origin, typically with sparse dark brown or black chromatophores, not forming any conspicuous pattern. Midline of flank generally with distinct longitudinal series of typically diffuse dark brown or black blotches, generally more evident on posterior half of flank. Blotches on flanks ranging from small to moderate in size; strongly faded in some specimens. Dorsal portion of body with conspicuous concentration of dark brown or black chromatophores at anterior and posterior origins of dorsal fin, adipose-fin base, and caudal-fin base, variably forming longitudinal series of four typically diffuse dark brown or black blotches. Posterior margin of body plates typically with dark brown or black chromatophores, variably forming Three new Corydoras from the rio Tapajós basin thin dark lines along border of plates. Dorsal-fin with conspicuous concentrations of dark brown or black chromatophores, forming small dark blotches; blotches roughly longitudinally or obliquely aligned in some specimens, variably fused with each other and forming stripes; blotches diffuse in some specimens. Pectoral and pelvic fins with sparse dark brown or black chromatophores, generally more concentrated on rays and not forming dark spots. Adipose fin with dark brown or black chromatophores, generally more numerous and concentrated on spine and on posterior portion of membrane, typically forming single dark patch; diffuse patch in some specimens. Anal fin with conspicuous concentrations of dark brown or black chromatophores, generally more evident on its anterior half, typically forming diffuse or conspicuous dark blotches roughly aligned transversally; blotches fused with each other, forming dark stripe in some specimens. Caudal fin with conspicuous concentrations of dark brown or black chromatophores, mainly on rays, forming dark blotches roughly aligned transversally in two to five slender bars; some specimens with diffuse blotches/bars.

Color in life.
Similar to color pattern of preserved specimens, but with light ground color of body and slightly more evident stripe from anteroventral portion of eye to upper lip lateral area. Body covered by greenish yellow iridescent coloration (Fig. 9). Aquarium specimens were observed to present dorsal and lateral surface of head plus lateral surface of cleithrum with irregular, rounded or vermiculated, conspicuous dark brown or black blotches, and conspicuous blotches on body. Some specimens with ground color of body greyish yellow (Fig. 10).
24/40 ni.bio.br | scielo.br/ni Three new Corydoras from the rio Tapajós basin Conservation status. Corydoras hypnos is currently known from its type locality and an additional record in its surroundings. However, both records are in the border of a conservation unit, the Floresta Nacional do Jamanxim, and no threat to the species as a whole is currently suspected. According to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019), Corydoras hypnos can be classified as Least Concern (LC). Diagnosis. Corydoras psamathos can be distinguished from its congeners, except for the species from the lineages 6, 7 and 9 sensu Alexandrou et al. (2011) plus C. difluviatilis, C. hastatus and C. pygmaeus, by having posterior margin of pectoral-fin spine with most serrations directed towards the tip of the spine (vs. most serrations directed towards origin of spine); from C. difluviatilis and C. pygmaeus it differs by the presence of contact between nuchal plate and posterior process of the parieto-supraoccipital (vs. absence of contact between nuchal plate and the posterior process of the parieto-supraoccipital); from C. hastatus by the absence of a large-sized dark blotch on caudal-fin base (vs. caudal-fin base region with a dark brown or black large blotch, roughly diamondshaped or rhomboid, or arrow-shaped, typically bordered anteriorly and posteriorly by conspicuously light areas); from the species within lineage 7, it differs by having posterodorsal edge of infraorbital 2 only in contact with sphenotic (vs. in contact with sphenotic and pterotic-extrascapular); from the species of lineages 6 and 9, except for C. concolor Weitzman, 1961, C. esperanzae Castro, 1987, C. guianensis, C. polystictus Regan, 1912, andC. sanchesi Nijssen &Isbrücker, 1967, by the absence of conspicuous dark brown or black markings on body; dark markings, when present, diffuse (vs. presence of conspicuous small-to large-sized dark brown or black markings in at least some region of the body); from C. concolor, C. esperanzae, C. guianensis, C. polystictus, and C. sanchesi by having posterior laminar expansion of infraorbital 2 strongly reduced, nearly imperceptible in some specimens (vs. posterior laminar expansion at least poorly developed, but clearly more developed and perceptible), by the slender body (vs. more robust), and by the narrower frontal bone (vs. wider). The new species can be further 25/40 ni.bio.br | scielo.br/ni Luiz Fernando C. Tencatt, Willian M. Ohara, Leandro M. Sousa and Marcelo R. Britto distinguished from C. concolor and C. esperanzae by the presence of ventral surface of trunk only with small-sized, irregular platelets (vs. ventral surface of trunk entirely or almost entirely covered by larger coalescent platelets); from C. sanchesi by having anterior portion of dorsal fin with scattered dark brown or black chromatophores, not forming any conspicuous pattern (vs. anterior portion of dorsal fin typically with a conspicuous concentration of dark brown or black chromatophores, forming a dark patch); from C. polystictus by presenting dorsal surface of snout with numerous platelets bearing odontodes (vs. dorsal surface of snout lacking platelets). Description. Morphometric data in Tab. 3. Head laterally compressed with convex dorsal profile, roughly triangular in dorsal view. Snout ranging from relatively short to moderately developed and generally smoothly rounded; slightly more rounded in some specimens. Head profile convex from tip of snout to anterior nares; ascending nearly straight or slightly convex from this point to dorsal-fin origin; region of frontal fontanel slightly concave in some specimens. Profile slightly convex along dorsal-fin base. Postdorsal-fin body profile slightly concave to adipose-fin spine, slightly concave from this point to caudal-fin base. Ventral profile of body nearly straight or slightly convex from isthmus to pectoral girdle, and slightly convex from this point until pelvic girdle. Profile nearly straight or slightly convex from pelvic girdle to base of first analfin ray, ascending slightly concave until caudal-fin base. Body roughly elliptical in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin.
Eye rounded, located dorsolaterally on head. Orbit delimited anteriorly by lateral ethmoid, anterodorsally by frontal, posterodorsally by sphenotic, posteroventrally by infraorbital 2, and anteroventrally by infraorbital 1. Anterior and posterior nares close to each other, only separated by flap of skin. Anterior naris tubular. Posterior naris close to anterodorsal margin of orbit, separated from it by distance similar to naris diameter. Mouth small, subterminal, width similar to bony orbit diameter. Maxillary barbel ranging from short to moderate in size, not reaching to anteroventral limit of gill opening. Outer mental barbel slightly longer than maxillary barbel. Inner mental barbel fleshy, base of each counterpart slightly separated from each other. Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout and isthmus.
Mesethmoid moderate in size, with anterior tip poorly developed, slightly smaller than 50% of bone length (see Britto, 2003:123, character 1, state 1; fig. 1B); posterior portion wide, partially exposed and bearing small odontodes. Nasal capsule delimited posteriorly and dorsally by frontal, anteriorly by mesethmoid, and ventrally and posteriorly by lateral ethmoid. Nasal slender, laterally curved, inner margin with poorly-to moderately-developed laminar expansion generally contacting frontal and mesethmoid; variably close but not in direct contact with mesethmoid; outer margin typically with strongly reduced laminar expansion. Lateral ethmoid slightly expanded anteriorly, with anterodorsal expansion relatively distant from nasal, and anterior margin contacting posterior portion of mesethmoid. Frontal elongated, narrow, width less than half of entire length; anterior projection short, size smaller than nasal length. Frontal fontanel large, slender, and somewhat ellipsoid; posterior tip extension slightly surpassing anterior margin of parieto-supraoccipital. Sphenotic somewhat trapezoid, contacting parieto-supraoccipital dorsally, pterotic-extrascapular posteriorly, second infraorbital posteroventrally and frontal anteriorly (Fig. 12A). Pterotic-extrascapular roughly pipe-shaped, with posteriormost portion contacting first lateral-line ossicle, posteroventral margin contacting cleithrum, and anteroventral margin contacting opercle; posterior expansion almost entirely covering lateral opening of swimbladder capsule, leaving slender area on its dorsal margin covered only by thick layer of skin. Parieto-supraoccipital wide, posterior process long and contacting nuchal plate; region of contact between posterior process and nuchal plate covered by thick layer of skin.
Two laminar infraorbitals with minute odontodes. Infraorbital 1 large, ventral laminar expansion ranging from poorly to moderately developed; anterior portion with laminar expansion moderately developed, reaching to middle portion of nasal capsule; inner laminar expansion poorly developed (Fig. 12A). Infraorbital 2 small, slender, with posterior laminar expansion strongly reduced, nearly imperceptible in some specimens; posteroventral margin contacting posterodorsal ridge of hyomandibula, posterodorsal edge contacting only sphenotic; inner laminar expansion ranging from strongly reduced to poorly developed (Fig. 12A). Posterodorsal ridge of hyomandibula close to its articulation with opercle relatively slender, exposed, and bearing small odontodes. Dorsal ridge of hyomandibula between pterotic-extrascapular and opercle typically covered by thick skin layer. Interopercle entirely covered by thick layer of skin; subtriangular, anterior projection ranging from moderately developed to relatively well developed. Preopercle elongated, relatively slender; minute odontodes on external surface. Opercle dorsoventrally elongated, with width similar to half of its entire length; free margin slightly convex, without serrations and covered by small odontodes.
Four branchiostegal rays decreasing in size posteriorly. Hypobranchial 1 deep; hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion ranging from strongly reduced, with only region of tip ossified, to well developed, its size about twice of cartilaginous portion. Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with small process on anterior margin of mesial portion; ceratobranchial 3 typically notched on postero-lateral margin; ceratobranchial 5 toothed on posterodorsal surface, with 28 to 38(3) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, with small pointed process on laminar expansion of posterior margin; epibranchial 3 with mesially-curved uncinate process on laminar expansion of posterior margin. Two wide pharyngobranchials (3 and 4); pharyngobranchial 3 with slightly triangular to smoothly rounded laminar expansion on posterior margin. Upper tooth plate roughly oval, 34 to 43(3) teeth aligned in two rows on posteroventral surface; rows closely aligned.
Lateral-line canal reaching cephalic laterosensory system through pteroticextrascapular, branching twice before reaching sphenotic: pterotic branch, with single pore, preoperculomandibular branch conspicuously reduced, with single pore opening at postotic main canal; postotic main canal widens just posterior to pterotic branch. Sensory canal continuing through pterotic-extrascapular, reaching sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, other branch connecting to frontal through supraorbital canal, both with single pore. Supraorbital canal branched, running through nasal bone. Epiphyseal branch conspicuously reduced; pore opening close to supraorbital main canal, directed towards frontal fontanel. Nasal canal typically with three openings, first on posterior edge, second on posterolateral portion, generally fused with first pore, and third on anterior edge. Infraorbital canal running through entire infraorbital 2, extending to infraorbital 1 and generally opening into two pores. Preoperculomandibular branch giving rise to preoperculo-mandibular canal, which runs through entire preopercle with three openings, leading to pores 3, 4, and 5, respectively.
Dorsal fin subtriangular, generally located just posterior to second dorsolateral body plate. Dorsal-fin rays II,7*(1) or II,8(19), posterior margin of dorsal-fin spine with 10 to 16 strongly reduced to poorly-developed serrations; most serrations directed towards tip of spine; some serrations variably perpendicularly directed; serrations absent close to origin of spine; small odontodes on anterior and lateral surfaces of spine (Fig. 12B). Nuchal plate moderately developed, almost entirely exposed, with minute odontodes. Spinelet short; spine moderately developed, with adpressed distal tip slightly surpassing posterior origin of dorsal-fin base. Pectoral fin roughly triangular, its origin just posterior to gill opening. Pectoral-fin rays I,7*(5), I,7,I(3) or I,8(12), posterior margin of pectoral spine with 17 to 26 strongly reduced to moderately-developed serrations along its entire length; most serrations directed towards tip of spine; some serrations perpendicularly directed; small odontodes on anterior, dorsal and ventral surfaces of spine (Fig. 12C). Anteroventral portion of cleithrum exposed; posterolateral portion of scapulocoracoid moderately developed, exposed, with anterior portion slightly expanded anteriorly, not in contact with anteroventral portion of cleithrum; exposed areas bearing small odontodes. Opening of axillary gland sensu Kiehl et al. (2006) located just posterior to pectoral-fin spine base. Pelvic fin oblong, located just below first or second ventrolateral body plate, and at vertical through first branched dorsal-fin ray. Pelvic-fin rays I,5*(20). Adipose fin roughly triangular, separated from base of last dorsal-fin ray by generally six dorsolateral body plates. Anal fin subtriangular, typically located just posterior to 12 th or 13 th ventrolateral body plates, and at vertical through adipose-fin spine base. Anal-fin rays ii,5(18), ii,5,i*(1), ii,7(1). Caudal fin bilobed, with dorsal and ventral lobes similar in size or dorsal lobe slightly larger than ventral lobe. Caudal-fin rays I,12,i*(20), generally five dorsal and ventral procurrent rays.
Typically, three laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, both bearing small odontodes; third, encased in third dorsolateral body plates. Body plates with minute odontodes scattered over exposed area, with conspicuous line of odontodes confined to posterior margins. Dorsolateral body plates 23(2), 24*(15) or 25(3). Ventrolateral body plates 21(15) or 22*(5). Dorsolateral body plates along dorsalfin base 6*(17) or 7(3). Dorsolateral body plates between adipose-and caudal-fin 7(2), 8*(17) or 9(1). Preadipose platelets 3*(14) or 4(6). Ventral surface of trunk between posteroventral margin of cleithrum and pelvic-fin origin laterally delimited only by first ventrolateral body plate; ventral portion of first ventrolateral body plate slightly expanded anteriorly. Small platelets covering base of caudal-fin rays. Small platelets disposed dorsally and ventrally between junctions of lateral plates on posterior portion of caudal peduncle. Anterior margin of orbit, above region of junction between frontal and lateral ethmoid, ventral margin of nasal capsule, above lateral ethmoid, and dorsal surface of snout with numerous small-to relatively large-sized platelets bearing odontodes; platelets on anterior margin of orbit and ventral margin of nasal capsule typically larger and coalescent. Ventral surface of trunk with scarce small-sized irregular platelets bearing odontodes; platelets more concentrated anteriorly and/or around pectoral-fin base.
Vertebral count 22(3); ribs 5(3); first pair conspicuously large, its middle portion closely connected to first ventrolateral body plate; its tip connected to anterior external process of basipterygium. Parapophysis of complex vertebra well developed.

Color in alcohol.
Overall color of body in Fig. 11. Ground color of body paleto brownish yellow or beige. Top of head dark brown; dark area typically extending mesially towards posterior tip of parieto-supraoccipital as thin longitudinal line. Dorsal and lateral surface of head and lateral surface of cleithrum with conspicuous concentrations of dark brown or black chromatophores, typically not forming blotches;  top of head with diffuse irregular dark blotches in some specimens; diffuse stripe from anteroventral portion of eye to upper lip lateral area typically present. Dorsolateral body plates with conspicuous concentration of dark brown or black chromatophores, typically not forming dark blotches; diffuse rounded, irregular or vertically elongated dark blotches in some specimens; dorsal portion of plates with slightly more concentrated chromatophores on anterior and posterior origins of dorsal fin, adipose-fin base, and caudal-fin base in some specimens. Ventrolateral body plates, except for ventral portion of plates between pelvic-fin origin to area just anterior to anal-fin origin, with conspicuous concentration of dark brown or black chromatophores, typically not forming dark blotches; diffuse rounded, irregular or vertically elongated dark blotches in some specimens; ventral portion of plates between pelvic-fin origin to area just anterior to anal-fin origin, especially around pelvic-fin origin, typically with sparse dark brown or black chromatophores, not forming any distinctive pattern. Midline of 30/40 ni.bio.br | scielo.br/ni Three new Corydoras from the rio Tapajós basin flank with distinct longitudinal series of diffuse dark brown or black blotches, more evident on posterior half of flank in single juvenile specimen (18.4 mm SL). Blotches on flanks typically small. Posterior margin of body plates typically with dark brown or black chromatophores, variably forming thin dark lines along border of plates. Dorsal-fin with dark brown or black chromatophores, especially on rays, generally not forming evident blotches; forming strongly faded to diffuse small dark blotches in some specimens; chromatophores typically more numerous and concentrated on dorsal half of first branched-ray region, including membranes, and along dorsal-fin proximal portion. Pectoral, pelvic, and anal fins with sparse to relatively numerous dark brown or black chromatophores, especially on rays, typically not forming dark spots; chromatophores on anal fin more concentrated on its proximal half. Adipose fin with conspicuous concentrations of dark brown or black chromatophores on spine; dark brown or black chromatophores on membrane typically more numerous and concentrated on its posterior margin and/or along its proximal portion, not forming any conspicuous pattern. Caudal fin with dark brown or black chromatophores, mainly on rays, typically forming closely-spaced, strongly faded to diffuse dark blotches; some specimens with blotches roughly aligned transversally in up to nine slender and closely-spaced rows of blotches; some specimens with non-aligned blotches; dark blotches variably absent. Color in life. Similar to color pattern of preserved specimens, but with light ground color of body and slightly more evident stripe from anteroventral portion of eye to upper lip lateral area. Body covered by greenish yellow iridescent coloration (Fig. 13). Some aquarium specimens with greyish-white ground color of body (Fig. 14).
Sexual dimorphism. Same as described for Corydoras hypnos.
Geographical distribution. Corydoras psamathos is currently known from the main channel of the rio Jamanxim and one of its tributaries, the igarapé Santa Júlia, rio Tapajós basin Novo Progresso Municipality, Pará State, Brazil (Fig. 5).
Ecological notes. The new species was observed to inhabit the rio Jamanxim and at least one of its tributaries, the igarapé Santa Júlia. In the rio Jamanxim, it was mostly associated with the margins of the river, where juvenile and adult specimens were observed in the shallow (up to about 20 cm deep) sandy shores with slow water flow. In the igarapé Santa Júlia (Fig. 15), juvenile and adult specimens were also observed associated in marginal shallow (up to about 20 cm deep) portions, with more Three new Corydoras from the rio Tapajós basin complex substrate, mainly composed by sand, fine gravel and larger rocks. In this site, both juvenile and adult specimens of C. psamathos were observed shoaling together with juvenile specimens of Corydoras sp. CW171, being the new species clearly more abundant. Additionally, C. apiaka was observed syntopically with the new species and Corydoras sp. CW171 in the igarapé Santa Júlia. In both sampled sites, the new species was mostly captured at night.
Etymology. The specific epithet "psamathos" refers to Psamathos Psamathides, the oldest wizard among the Psamathists, the sand sorcerers, a fictional character created by J. R. R. Tolkien in his book Roverandom. The name derives from the Greek psammos, which means sand. The name alludes to the sand-dwelling behavior of the new species. A noun in apposition.

Conservation status.
Corydoras psamathos is currently known from its type locality and an additional record from the same region. Although the region is severely impacted by anthropic action, no threat to the species as a whole is currently suspected. According to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019), Corydoras psamathos can be classified as Least Concern (LC).

DISCUSSION
The presence of syntopic species sharing similar color patterns but distinct morphology has been widely reported for Corydoras (e.g., Nijssen, Isbrücker, 1980a,c;Britto, 2003;Britto et al., 2009;Alexandrou et al., 2011;Tencatt et al., 2013Tencatt et al., , 2019Tencatt, Pavanelli, 2015;Tencatt, Britto, 2016;Tencatt, Ohara, 2016a,b;Lima, Sazima, 2017), having almost certainly played an important role in the evolution of the group . These convergent color patterns were generally reported as cases of Müllerian mimicry (Alexandrou et al., 2011), with a single mention to the Batesian mode of mimicry (Lima, Sazima, 2017). During the fieldwork, it was possible to observe C. thanatos and C. hypnos, which share similar color patterns but clearly different general morphological patterns, shoaling together in some sites. The same was observed between C. psamathos and Corydoras sp. CW171. Considering that the four species present the defensive tripod formed by their pungent dorsal and pectoral spines (Fine, Ladich, 2003), allied to the presence of axillary glands sensu Kiehl et al. (2006), all of them can be considered as unpalatable. Therefore, it seems reasonable to conclude that these pairs of species compose two Müllerian mimicry rings (see Alexandrou et al., 2011). The Serra do Cachimbo is one of the highest elevations of the Brazilian Shield, located on the southernmost border of the Amazon basin. The mountain chain can reach 500 meters above the sea level and forms an arc, running from Southeast to Northwest dividing the headwaters of the middle rio Xingu basin to the East (rio Curuá basin) and the middle rio Tapajós basin to the West (headwaters of the rio Jamanxim basin and tributaries of the rio Teles Pires) (Goulding et al., 2003). Goulding et al. (2003) identified the Serra do Cachimbo as an area with high endemism, a theory proven in following years by the description of a relatively high number of fish species reported as endemic to this region (e.g., Lima, Birindelli, 2006;Birindelli, Britski, 2009;Sousa et al., 2010;Netto-Ferreira, 2012;Netto-Ferreira et al., 2013;Datovo, 2014;Varella, Sabaj Pérez, 2014;Varella, Britzke, 2016;Garcia-Ayala et al., 2017;Oyakawa et al., 2018). Even though the specimens analyzed herein were not captured in the Serra do Cachimbo itself, they were recorded from an area in its surroundings (especially C. thanatos and C hypnos), in the upper portion of the rio Jamanxim, which drains part of the Serra do Cachimbo. This explains the reason why the three new species together with Corydoras sp. CW111 and CW171 are called the "Serra do Cachimbo Corydoras" in the aquarium trade (see Lucanus, 2021).
Until recently, the area was relatively poorly sampled, but four major scientific expeditions were carried out in the early twenty-first century (for more details about those expeditions, see . One of them was the PIPE Expedition, funded by the US National Science Foundation project "All Catfish Species Inventory" (DEB-0315963 PI José Birindelli), the first scientific endeavor to the Cachimbo that shared its results on the internet. In this way, photos of live specimens were published in a report-like website in 2008 (http://silurus.acnatsci.org/ACSI/field/Pipe_Expedition/ Home.html), making the species of the region known around the world. Some species depicted on the website immediately got the attention of fish-keeping hobbyists around the world, such as Apistogramma sp. "gigas" (later described as Apistogramma kullanderi Varella & Sabaj Pérez, 2014) and Corydoras sp. "bonita" (= Corydoras sp. CW111), both reported from the rio Curuá.
The demand for these species by aquarists made exporters focus their efforts on catching these fishes in the Serra do Cachimbo region. Fishermen from several places in Brazil (as well as from Colombia and Peru) traveled to the area and extensively seined the tributaries of the rio Curuá in order to capture the new fishes. Apistogramma kullanderi and A. eleutheria Varella & Britzke, 2016 were exported in great numbers, mainly to Asia, but also to Europe and North America, and have been successfully bred in captivity (O. Lucanus, 2022, pers. comm.;LMS pers. obs.). However, the impact of so many individuals being removed from wild populations of species with restrict geographical distribution is yet to be fully understood. In a recent expedition to the rio Curuá tributaries at the Serra do Cachimbo, very few specimens of A. kullanderi were spotted during field observations (O. Lucanus, 2022, pers. comm.), and the habitat was considerably impacted by fishing activity (e.g., clearly overturned substrate, and disposed collection gear), in addition to the habitat degradation on the surroundings caused by the paving works of the BR-163 road, which runs close to these sites.
The absence of Corydoras CW111 in the most recent survey efforts, as well as reports from several fishermen of the scarcity of this species, brings a real concern. Is this species naturally rare, or was it overfished to supply the ornamental trade? Perhaps both factors combined. The capture of wild fishes to supply the ornamental fish trade is an activity that can be beneficial to both local human populations and ecosystems if made in a sustainable way (see Evers et al., 2019;. However, the over-exploitation of a species caused by the ornamental trade can lead to a series of negative impacts (Dey, 2016;Evers et al., 2019;, especially in the case of narrowly endemic species with naturally low abundance, which are often already affected by the local environmental degradation itself. This delicate balance between allowing local people to profit from native species found in their region, and affording an alternative income stream to the much more destructive practices (e.g., gold mining, logging, industrial agriculture) (for a broader discussion on this theme, see Evers et 36/40 ni.bio.br | scielo.br/ni Three new Corydoras from the rio Tapajós basin al., 2019), and the potential damage to some species with small and/or geographically restricted populations, especially in the fragile headwater streams of the Xingu and Tapajós basins, is a difficult and elusive problem that requires further study and input from all stakeholders.