Two new species of Corydoras Lacépède , 1803 ( Siluriformes : Callichthyidae ) from the rio Madeira basin , Brazil

Two new species of Corydoras are described from the rio Madeira basin, Brazil. The intermediate long-snouted new species can be distinguished from its congeners by presenting the following combination of features: posterior margin of dorsalfin spine with laminar serrations directed towards the origin of the spine; presence of two longitudinal black stripes on flanks; anterior portion of dorsal fin with sparse black chromatophores, not forming any conspicuous pattern; absence of a conspicuous black marbled coloration pattern on head; black spots on caudal fin, some spots arranged, forming transversal bars; and brownish dorsal-fin spine. The short-snouted new species can be distinguished from its congeners by the following combination of features: short mesethmoid; posterior laminar expansion of infraorbital 2 very reduced, not in contact with compound pterotic; two or three longitudinal black stripes on flanks; absence of an oblique or vertical black blotch across the eye; anterior portion of dorsal fin with sparse black chromatophores, not forming any conspicuous pattern; and ventral surface of trunk naked or covered by sparse platelets.


Introduction
Corydoras Lacépède, 1803 is the most species-rich genus of Siluriformes, comprising approximately 170 valid species (Reis, 2003;Eschmeyer, 2015).The genus is widely distributed in cis-andean South America and the largest diversity is found in the Amazon basin, where more than the half of the known species occurs (see Eschmeyer, 2015).The species inhabit many different environments, from lakes and streams to large rivers.Typically found in shallow depths or close to the margins, Corydoras are often associated with sandy or muddy substrates.
Efforts to understand the taxonomy and systematics of Corydoras have included Ellis (1913), Gosline (1940), Nijssen (1970), Nijssen & Isbrücker (1980), Britto (2003) and Alexandrou et al. (2011).Multiple studies have noted apparent cases of convergence of color pattern in Corydoras.Nijssen & Isbrücker (1980) were the first to implicitly recognize a convergent color pattern by placing C. arcuatus Elwin, 1939 andC. narcissus Nijssen &Isbrücker, 1980, two species with almost equal color pattern, into two different morphological groups, and noting that C. narcissus is more similar to C. acutus Cope, 1872than to C. arcuatus. Britto et al. (2009) later described a third species with very similar color pattern to C. arcuatus and C. narcissus and showed that all three species belong to distinct clades.Based on phylogenetic analyses, Britto (2003) noted another case of apparent color convergence involving Corydoras nattereri Steindachner, 1876 in the Corydoras clade and C. prionotos Nijssen & Isbrücker, 1980 in the Scleromystax clade.Alexandrou et al. (2011) study of community structure in Corydoradinae was the first paper to explicitly hypothesize an adaptive basis for the convergence of color patterns in Corydoras.The study was based on a molecular phylogenetic analysis that established nine well-defined clades -each with characteristic snout morphology.The authors noted multiple cases of apparent convergence of color pattern within syntopic representatives of these clades, and provided evidence to support a hypothesis of Müllerian co-mimicry.
With recent survey efforts undertaken by the project "Monitoramento e Conservação da Ictiofauna do rio Madeira" (Assessment and conservation of the ichthyofauna of the rio Madeira) from 2009 to 2013.Britto (2013) documented 14 species of Corydoras from the Brazilian territory of the rio Madeira basin (but mentioned the occurrence of as many as twenty species).Here we report a new case of convergent color pattern in Corydoras.During a recent field expedition in the rio Aripuanã and its tributaries in the rio Madeira basin, two new species with similar color pattern but showing divergent snout morphology were found.In this paper, we describe these two sympatric and syntopic species and demonstrate that although they have similar color pattern, they belong to clearly distinct morphological groups that correspond to different lineages sensu Alexandrou et al. (2011).

Material and Methods
Measurements were obtained through digital calipers to the nearest tenth of millimeter.Morphometric and meristic data were taken following Reis (1997), with modifications of Tencatt et al. (2013).Morphometrics are reported as percentages of standard length (SL) and head length (HL).Homology and terminology of barbels follows Britto & Lima (2003).For our osteological analysis, some specimens were cleared and stained (c&s) following the protocol of Taylor & Van Dyke (1985).Osteological terminology was based on Reis (1998), except for the use of parietosupraoccipital instead of supraoccipital (Arratia & Gayet, 1995), compound pterotic instead of pterotic-supracleithrum (Aquino & Schaefer, 2002), and scapulocoracoid instead of coracoid (Lundberg, 1970).Nomenclature of latero-sensory canals and preopercular pores are according to Schaefer & Aquino (2000) and Schaefer (1988), respectively.The supra-preopercle sensu Huysentruyt & Adriaens (2005) will be treated here as a part of the hyomandibula according to Vera-Alcaraz (2013).Vertebral counts include only free centra, with the compound caudal centra (preural 1+ ural 1) counted as a single element.Terminology of snout external morphology follows Alexandrou et al. (2011).In the description and diagnosis, the dark longitudinal stripes were counted only when well defined, continuous and not fused to the blackened dorsal portion of the fish's body.
In the description, numbers between brackets represent the total number of specimens with those counts.Numbers with an asterisk refer to the counts of the holotype.

Corydoras brittoi, new species
urn:lsid:zoobank.org:act:3F9B3430-8D4C-4180-9B82-1E70648E7BD1 (Figs.1-2a,b, 3a,c, 4 Barros. INPA 48032, 4, 34.7-36.7 mm SL;MCP 48747, 3, 34.5-39.0 mm SL;MNRJ 43573, 4, 32.7-36.8 mm SL;MZUSP 117334, 5, 35.4-37.5 mm SL;NUP 17312, 4, 34.8-37.4 mm SL;NUP 17313, 2 c&s, 31.4-34.1 mm SL; same data as the holotype. Diagnosis.Corydoras brittoi can be distinguished from all of its congeners, with exception of the species from 'lineage 8' sensu Alexandrou et al. (2011), by the presence of posterior margin of dorsal-fin spine with laminar serrations directed towards the origin of the spine (vs.serrations, when present, conical; directed towards dorsal-fin spine tip in the members of the remaining lineages).Corydoras brittoi can be distinguished from other members of 'lineage 8', with exception of C. bifasciatus Nijssen, 1972, C. pinheiroi Dinkelmeyer, 1995 andC. pulcher, by the presence of two longitudinal black stripes on flanks (vs.presence of a single arched black stripe on dorsal portion of flank in C. arcuatus; stripe, when well defined, located on midline of flank in C. gomezi, C. incolicana Burgess, 1993, C. leopardus, C. orphnopterus, C. robineae Burgess, 1983 andC. robustus; three to four slender longitudinal black stripes on flanks in C. ornatus; presence of three to four longitudinal rows of black spots on flanks, which may be coalescent and form stripes in some specimens of C. haraldschultzi, C. isbrueckeri, C. noelkempffi and C. spectabilis; absence of stripes on flanks in remaining species).Corydoras brittoi can be distinguished from C. bifasciatus and C. pulcher by presenting anterior portion of dorsal fin with sparse black chromatophores, not forming any conspicuous pattern (vs.conspicuously blackened in C. bifasciatus; hyaline with conspicuous whitish yellow pigmentation in C. pulcher); from C. pinheiroi by the absence of a conspicuous black marbled coloration pattern on head (vs.presence).Additionally, Corydoras brittoi can also be distinguished from C. bifasciatus by the presence of black spots on caudal fin, some spots arranged, forming transversal bars (vs.spots absent, covered by brown chromatophores); from C. pulcher by the presence of brownish dorsal-fin spine (vs.conspicuously whitish yellow).Description.Morphometric data presented in Table 1.Head compressed with acutely convex dorsal profile; triangular in dorsal view.Snout pointed and straight.Head profile nearly straight from tip of snout to anterior nare; ascending nearly straight from this point to tip of posterior process of parietosupraoccipital.Profile slightly convex along dorsal-fin base.Postdorsal-fin body profile nearly straight to adipose-fin spine; concave from this point to caudal-fin base.Ventral profile of body slightly convex from isthmus to base of first anal-fin ray; concave from this point to caudal-fin base.Body acutely elliptical in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin.
Eye rounded, located dorso-laterally on head; orbit delimited dorsally by lateral ethmoid, frontal and sphenotic, ventrally by infraorbitals.Anterior and posterior nares close to each other, only separated by flap of skin.Anterior naris tubular.Posterior naris relatively distant to anterodorsal margin of orbit, separated from it by distance equal to twice of naris diameter.Mouth small, subterminal, width nearly equal to bony orbit diameter.Maxillary barbel relatively large, almost reaching anteroventral limit of gill opening.Outer mental barbel slightly larger than maxillary barbel.Inner mental barbel fleshy, with base close to its counterpart.Small rounded papillae covering entire surface of all barbels, upper and lower lips, and isthmus.
Mesethmoid long; anterior tip well developed, larger than 50% of bone length (see Britto, 2003: 123, character 1, state 0; fig.1A); posterior portion conspicuously narrow and entirely covered by a thick layer of skin.Nasal slender, curved laterally, with very reduced laminar expansion on its inner margin; mesial border contacting only frontal.Frontal elongated, narrow, with width slightly smaller than half of entire length; anterior projection short, size smaller than nasal length.Frontal fontanel large, oblong; posterior tip extension slightly entering anterior margin of parietosupraoccipital.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 poorly developed; anterior portion with well-developed expansion (Fig. 2a); infraorbital 2 small, slender; with posterior laminar expansion well developed; posteroventral margin contacting posterodorsal ridge of hyomandibula, dorsal tip contacting sphenotic and compound pterotic (Fig. 2b).Posterodorsal ridge of hyomandibula close to its articulation with opercle oblong; exposed, conspicuously slender; dorsal ridge of hyomandibula between compound pterotic and opercle covered by thick layer of skin; exposed  Four branchiostegal rays decreasing in size posteriorly.Hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion well developed, about twice size of cartilaginous portion.Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with a very reduced process on anterior margin of mesial portion; ceratobranchial 3 notched on postero-lateral margin; ceratobranchial 5 toothed on postero-dorsal surface, 34 to 36 (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 somewhat quadrangular uncinate process on laminar expansion of posterior margin.Two wide pharyngobranchials (3 and 4), pharyngobranchial 3 with a rippled laminar expansion on posterior margin.Upper tooth plate oval; 34 to 40 (2) teeth aligned in two rows on postero-ventral surface.
Lateral-line canal entering neurocranium through compound pterotic, splitting into two branches before entering sphenotic: pterotic branch with a single pore; preoperculomandibular branch conspicuously reduced, with a single pore opening close to postotic main canal.Sensory canal continuing through compound pterotic, entering sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, other branch entering frontal through supraorbital canal, both with single pore.Supraorbital canal not branched, running through nasal bone.Epiphyseal pore opening at supraorbital main canal; slightly directed toward frontal fontanel region.Nasal canal with three openings, first on posterior edge, second on posterolateral portion and third on anterior edge.Infraorbital canal running through entire second infraorbital, extending to infraorbital 1 and 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 triangular, located just posterior to second dorsolateral body plate.Dorsal-fin rays II,8, posterior margin of dorsal-fin spine 11 to 14 moderately-developed serrations directed towards dorsal-fin spine origin; serrations absent proximally (Fig. 3a).Nuchal plate moderately developed; exposed, with minute odontodes; spinelet short; spine moderately developed, adpressed distal tip reaching to or slightly surpassing origin of last dorsal-fin branched ray; anterior margin with small odontodes.Pectoral fin triangular, its origin just posterior to gill opening.Pectoralfin rays I,8 (17), I,9* (3); posterior margin of pectoral-fin spine with 17 to 19 moderately-developed laminar serrations along its entire length; serrations directed towards pectoralfin spine origin (Fig. 3c).Pelvic fin oblong, located just below first ventrolateral body plate, and at vertical through first branched dorsal-fin ray.Pelvic-fin rays i,5.Adipose fin roughly triangular, separated from base of last dorsalfin ray by generally six dorsolateral body plates.Anal fin triangular, located just posterior to 13 th ventrolateral body plates, and at vertical through anterior margin of adiposefin spine.Anal-fin rays ii,6.Caudal-fin rays i,12,i, generally five dorsal and ventral procurrent rays; bilobed; dorsal lobe generally slightly larger than ventral lobe.

Sexual dimorphism.
Except for the presence of lanceolate genital papilla in males, which occurs in all Corydoradinae (see Nijssen & Isbrücker, 1980;Britto, 2003), no other sexually dimorphic feature was observed.
Distribution.The new species is known from the rio Aripuanã basin, Mato Grosso State (Fig. 5).

Ecological notes.
The type locality of Corydoras brittoi is located at 110 meters above sea level, and is a small clear water stream, with 2-3 m width and 0.5-2 m depth, with preserved riparian vegetation, swift water current, and bottom composed mainly of sand and dead leaves.Specimens of C. brittoi were observed at night during capture at shallow portions of the stream in small groups (5-15 individuals), and sometimes associated with a other new species described below.

Etymology. Corydoras brittoi is named in honor of
Marcelo Ribeiro de Britto, a dear friend and mentor, for his extensive contributions to the taxonomy and systematics of the Corydoradinae.A genitive.

Conservation status.
Corydoras brittoi is so far known only from the type-locality and its conservation status is uncertain based on the limited knowledge of its geographic distribution.However, considering that important threats to the species were not detected in the area, and that it occurs in a protected area (Reserva Extrativista Guariba Roosevelt), Corydoras brittoi would be classified as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2014).(Figs.2c,d, 3b,d, 6 Paratypes.INPA 48033, 5, 22.5-23.2 mm SL;MCP 48748, 5, 19.0-23.5 mm SL;MZUSP 117335, 10, 21.8-25.4 mm SL;NUP 17314, 17, 20.8-30.7 mm SL; NUP 17315, 3 c&s, 24.7-26.8mm SL; ZUFMS-PIS 4064, 8, 20.0-22.9mm SL; same data as the holotype. Diagnosis.Corydoras pavanelliae can be distinguished from its congeners, with exception of species from lineages '4', '5', '6', '7' and '9' sensu Alexandrou et al. (2011) by the presence of a short mesethmoid, with anterior portion smaller than 50% of the bone length (vs.long, equal or larger than 50% of the bone length).Corydoras pavanelliae can be distinguished from species of lineages '4', '5' and '7' sensu Alexandrou et al. (2011) by the absence of contact between infraorbital 2 and compound pterotic (Figs.2c,d Steindachner, 1906, C. nattereri, C. sipaliwini, C. trilineatus Cope, 1872; a longitudinal series of large black blotches along midline of flank in C. diphyes Axenrot & Kullander, 2003, C. ehrhardti Steindachner, 1910, C. flaveolus Ihering, 1911, C. longipinnis Knaack, 2007, C. paleatus (Jenyns, 1842), C. reynoldsi Myers &Weitzman, 1960 andC. tukano Britto &Lima, 2003; flanks densely covered by small rounded black spots, which can be diffuse or absent in some specimens, in C. albolineatus Knaack, 2004 andC. potaroensis Myers, 1927; a single oblique black stripe from dorsal-fin base region descending to base of caudal peduncle in C. melini Lönnberg & Rendahl, 1930; four to six longitudinal rows of black spots on flanks, which may be coalescent and form stripes in some specimens of C. sterbai Knaack, 1962;   Description.Morphometric data presented in Table 1.Head compressed with convex dorsal profile; triangular in dorsal view.Snout short and slightly pointed.Head profile convex from tip of snout to anterior nares; ascending nearly straight from this point to tip of posterior process of parieto-supraoccipital; region just anterior to nares slightly concave in some specimens.Profile slightly convex along dorsal-fin base.Postdorsal-fin body profile nearly straight to adipose-fin spine; concave from this point to caudal-fin base.Ventral profile of body slightly convex from isthmus to pelvic girdle.Profile nearly straight from pelvic girdle to base of first anal-fin ray; abruptly concave from this point to caudal-fin base.Body roughly elliptical in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin.
Eye rounded, located dorso-laterally on head; orbit delimited dorsally by lateral ethmoid, frontal and sphenotic, ventrally by infraorbitals.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 equal to naris diameter.Mouth small, subterminal, width nearly equal to bony orbit diameter.Maxillary barbel moderate in size, not reaching anteroventral limit of gill opening.Outer mental barbel slightly larger than maxillary barbel.Inner mental barbel fleshy, base slightly separated to its counterpart; insertion of barbel in middle of lower lip.Small rounded papillae covering entire surface of all barbels, upper and lower lips, and isthmus.
Mesethmoid short; anterior tip moderately developed, smaller than 50% of bone length (see Britto, 2003: 123, character 1, state 1; fig.1B); posterior portion relatively wide and entirely covered by thick layer of skin.Nasal slender, curved laterally, with inner margin laminar; mesial border contacting only frontal.Frontal elongated, narrow, with width slightly smaller than half of entire length; anterior projection short, size smaller than nasal length.Frontal fontanel large, oval; posterior tip extension slightly entering anterior margin of parieto-supraoccipital.Parietosupraoccipital 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 poorly developed; moderately developed in larger specimens (see Britto, 2003: 128, fig. 5B); anterior portion with well-developed expansion (Fig. 2c); infraorbital 2 small, slender; with posterior laminar expansion very reduced; posteroventral margin contacting posterodorsal ridge of hyomandibula, dorsal tip contacting only sphenotic (Fig. 2d).Posterodorsal ridge of hyomandibula close to its articulation with opercle oblong; slender, exposed and bearing small odontodes; dorsal ridge of hyomandibula between compound pterotic and opercle covered by thick layer of skin.Interopercle entirely covered by thick layer of skin, somewhat triangular, anterior projection well-developed.Preopercle slender, elongated, minute odontodes sparse on external surface.Opercle elongated dorso-ventrally, width smaller than half of its length; free margin smoothly convex, without serrations and covered by small odontodes.Anteroventral portion of cleithrum and posterolateral portion of scapulocoracoid exposed; minute odontodes sparse on exposed areas.Vertebral count 21 (3); ribs 6 (3), first pair conspicuously large; complex vertebra compact in shape.Neural and haemal spines with pointed distal tips.
Four branchiostegal rays decreasing in size posteriorly.Hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion well developed, about twice size 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; ceratobranchial 5 toothed on postero-dorsal surface, 33 to 39 (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 curved mesially uncinate process on laminar expansion of posterior margin.Two wide pharyngobranchials (3 and 4), pharyngobranchial 3 with small triangular laminar expansion on posterior margin.Upper tooth plate oval; 41 to 43 (3) teeth aligned in two rows on postero-ventral surface.
Lateral-line canal entering neurocranium through compound pterotic, splitting into two branches before entering sphenotic: pterotic branch with a single pore; preoperculomandibular branch conspicuously reduced, with a single pore opening close to postotic main canal.Sensory canal continuing through compound pterotic, entering sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, other branch entering frontal through supraorbital canal, both with a single pore.Supraorbital canal not branched, running through nasal bone.Epiphyseal pore opening at supraorbital main canal.Nasal canal with three openings, first on posterior edge, second on posterolateral portion and third on anterior edge.Infraorbital canal running through entire second infraorbital, extending to infraorbital 1 and 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 triangular, located just posterior to second dorsolateral body plate.Dorsal-fin rays II,8, posterior margin of dorsal-fin spine with nine to 12 reduced serrations directed towards tip of spine; serrations absent proximally (Fig. 3b).Nuchal plate moderately developed; exposed, with minute odontodes; spinelet short; spine relatively large, adpressed distal tip surpassing last dorsal-fin branched ray origin; anterior margin with small odontodes.Pectoral fin triangular, its origin just posterior to gill opening.Pectoral-fin rays I,8 (17), I,9* (3); posterior margin of pectoral-fin spine with 17 to 22 small serrations along its entire length; serrations directed towards pectoral-fin spine tip (Fig. 3d).Pelvic fin oblong, located just below first ventrolateral body plate, and at vertical through first branched dorsal-fin ray.Pelvic-fin rays i,5.Adipose fin roughly triangular, separated from base of last dorsal-fin ray by generally six dorsolateral body plates.Anal fin triangular, located just posterior to 12 th ventrolateral body plates, and at vertical through anterior margin of adipose-fin spine.Anal-fin rays ii,6.Caudal-fin rays i,12,i, generally four dorsal and ventral procurrent rays; bilobed; dorsal lobe generally slightly larger than ventral lobe.

Color in alcohol.
Overall color of body in Fig. 6.Ground color of body light yellow, with top of head and snout dark brown; parieto-supraoccipital entirely dark brown.Maxillary barbel and proximal region of outer mental barbel covered by black chromatophores.Anterior portion of body with irregular black blotches.Posterior margin of first and second dorsolateral body plates blackened.Dorsal portion of body irregularly black pigmented, forming diffuse slender longitudinal black stripe, more conspicuous from dorsal-fin base to adipose-fin origin.Body with two or three conspicuous longitudinal black stripes.Medial portion of dorsal half of dorsolateral body plates with black blotches anteriorly to adipose fin; blotches aligned forming short and narrow longitudinal stripe below dorsal-fin base in some specimens.Midventral half of dorsolateral body plates blackened, forming broad longitudinal stripe along flank.Dorsal half of medial portion of ventrolateral body plates blackened, forming slender longitudinal black stripe along flank; stripe absent or diffuse posteriorly to analfin last branched ray region.Dorsal fin covered by sparse brown chromatophores, more concentrated on its base; upper half of first and second dorsal-fin rays, including membranes, with more concentrated black chromatophores; dorsal-fin spine brownish.Pectoral-fin rays with sparse black chromatophores; pectoral-fin spine brownish.Pelvic fin hyaline.Adipose fin with posterior margin brownish or blackened; adipose-fin spine dorsal half blackened.Caudal fin with scattered brownish chromatophores; black spots arranged in one to four transversal black bars; bars diffuse or absent in some specimens; caudal-fin base blackened; region just posterior to caudal fin base hyaline and with light yellow pigmentation.
Sexual dimorphism.Except for the presence of lanceolate genital papilla in males, which occurs in all Corydoradinae (see Nijssen & Isbrücker, 1980;Britto, 2003), no other sexually dimorphic feature was observed.
Distribution.The new species is known from its typelocality, a tributary to the rio Aripuanã, Mato Grosso State (Fig. 5).

Discussion
In general, Corydoradinae species with convergent color pattern can be clearly distinguished from each other by snout morphology (see Alexandrou et al., 2011: 2, fig. 1).Corydoras pavanelliae presents the general morphological features common to lineages '6' and '9' sensu Alexandrou et al. (2011), both characterized mainly by (I) the presence of a short mesethmoid; (II) posterior margin of the pectoralfin spine with serrations generally directed towards the tip of the spine; (III) infraorbital 1 generally with poorly to moderately developed ventral laminar expansion; and (IV) infraorbital 2 generally not contacting compound pterotic.Despite both lineages sharing some general external morphology, Alexandrou et al. (2011) and Vera-Alcaraz (2013) found evidence that these two clades do not form a monophyletic group.However, most of Alexandrou et al.'s (2011) phylogenetic inferences are based on molecular characters, which are not yet available for C. pavanelliae.Therefore, it is as yet not possible to clearly determine which lineage C. pavanelliae belongs to.
On the other hand, Corydoras brittoi presents the typical intermediate long snout pattern, which is present in most species from the 'lineage 8' sensu Alexandrou et al. (2011).The species from the 'lineage 8', with exception of C. difluviatilis Britto &Castro, 2002 andC. garbei Ihering, 1911, can be distinguished from the other congeners by the presence of dorsal-fin spine with serrations directed towards the origin of the spine.Other features common to species of the lineage 8 are (I) the presence of long mesethmoid; (II) laminar serrations on posterior margins of dorsal-and pectoral-fin spines; (III) infraorbital 1 generally with poorly to moderately developed ventral laminar expansion; and (IV) infraorbital 2 contacting compound pterotic.Despite the fact that C. difluviatilis and C. garbei are recognized as belonging to lineage 8 according to Alexandrou et al. (2011), they display a morphological pattern much closer to the species of 'lineage 7', which can be characterized by (I) the presence of rounded snout; (II) serrations on dorsaland pectoral-fin spines, when present, poorly developed and directed towards the tip of the spines; (III) ventral laminar expansion of infraorbital 1 very large; and (IV) infraorbital 2 contacting compound pterotic.Therefore, the phylogenetic positions of C. difluviatilis and C. garbei, may require further investigation.Notwithstanding these two exceptions, C. brittoi shares the same serration pattern of the dorsal-fin observed in all of the species from the lineage 8 sensu Alexandrou et al. (2011).
With the two new species described here, a total of 42 species are known from the rio Madeira basin.This represents 24.7% of all Corydoras diversity.Corydoras

Fig. 3 .
Fig. 3. Dorsal-and pectoral-fin spines of (a, c) Corydoras brittoi, NUP 17313, 34.1 mm SL, showing serrations directed towards the origins of the spines on posterior margins of the (a) dorsal-fin spine (8.6 mm long) and of the (c) right pectoral-fin spine (8.9 mm long), and of (b, d) Corydoras pavanelliae, NUP 17315, 26.8 mm SL, showing serrations directed towards the tips of the spines on posterior margins of the (b) dorsal-fin spine (7.9 mm long) and of the (d) right spine (7.6 mm long).

Fig. 4 .
Fig. 4. Specimen of Corydoras brittoi photographed in life, showing the iridescent greenish yellow coloration all over the body.

Fig. 5 .
Fig. 5. Map showing the type-locality (red circle) of Corydoras brittoi and Corydoras pavanelliae, a tributary to the rio Guariba, Mato Grosso.The blue triangle represents the Igarapé Pica-Pau, also a tributary to the rio Guariba, and the yellow triangle represents the rio Aripuanã, both representing additional records of C. brittoi.
presence of a single arched black stripe on dorsal portion of flank in C. urucu; absence of stripes on flanks in remaining species).Corydoras pavanelliae can be distinguished from C. axelrodi, C. evelynae, C. loxozonus, C. parallelus, C. schwartzi and C. surinamensis by the absence of an oblique or vertical black blotch across the eye (vs.presence); from C. axelrodi, C. evelynae, C. loxozonus, C. parallelus and C. surinamensis by presenting anterior portion of dorsal fin with sparse black chromatophores, not forming any conspicuous pattern (vs.entirely or almost entirely conspicuously blackened); from C. evelynae and C. schwartzi by having ventral surface of trunk naked or covered by sparse platelets (vs.densely covered by coalescent platelets).
brittoi and C. pavanelliae can be distinguished from all of their congeners in the rio Madeira basin, with the exception of C. bilineatus, C. pinheiroi and C. pygmaeus, by the presence of two to three (up to three only in some specimens of C. pavanelliae) longitudinal black stripes on flanks (vs. a single longitudinal black stripe in C. acutus, Corydoras aff.bondi, Corydoras cf.trilineatus; three to four longitudinal rows of black spots on flanks, which may be coalescent and form stripes in some specimens of C. haraldschultzi, C. isbrueckeri, C. noelkempffi, C. spectabilis, C. sterbai; a single black stripe on dorsal portion of flank in C. arcuatus, C. gracilis and C. narcissus; conspicuous stripes absent in the remaining species).Both new species presented herein can be distinguished from C. bilineatus and C. pinheiroi by the absence of a black marbled coloration on anterior portion of the body (vs.presence), and from C. pygmaeus by the presence of contact between nuchal plate and posterior process of the parieto-supraoccipital (vs.absence).

Table 1 .
Morphometric data for Corydoras brittoi and Corydoras pavanelliae.N= number of measured specimens and SD = standard deviation.
areas bearing small odontodes.Interopercle covered by thin layer of skin, somewhat triangular, anterior projection well-developed.Preopercle slender, elongated, minute odontodes sparse on external surface.Opercle elongated dorso-ventrally, width smaller than half of its length; free margin convex, without serrations and covered by small odontodes.Anteroventral portion of cleithrum and posterolateral portion of scapulocoracoid exposed; minute odontodes sparse on exposed areas.Vertebral count 22 (2); ribs 7 (2), first pair conspicuously large; complex vertebra slender in shape.Neural and haemal spines with pointed distal tips.

, Table 1)
The only known specimens of Corydoras pavanelliae were collected among C. brittoi specimens.For notes on its ecology, see Ecological notes of C. brittoi.Corydoras pavanelliae is named in honor of Carla Simone Pavanelli, advisor of the first author and dear friend, for her extensive contributions to the knowledge of the ecology and taxonomy of the Neotropical fishes.A genitive.The known specimens of Corydoras pavanelliae are relatively numerous and were collected among C. brittoi specimens.For this reason, we also suggest that C. pavanelliae would be classified as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2014).