Neotropical Ichthyology

Original article

https://doi.org/10.1590/1982-0224-2023-0112

urn:lsid:zoobank.org:pub:95847932-0AAA-4024-8BB3-69684368D313

A new long-snouted Corydoras(Siluriformes: Callichthyidae) fromthe rio Xingu and rio Tapajós basins,
Brazilian Amazon
Correspondence:
Luiz Fernando Caserta Tencatt
luiztencatt@hotmail.com

Submitted October 10, 2023
Accepted November 21, 2023
by Claudio Oliveira
Epub February 12, 2024

Luiz Fernando Caserta Tencatt1, Ondina Lillan Pinto do Couto2,
Sérgio Alexandre dos Santos3 and Leandro Melo de Sousa2

A new species of Corydoras is described from the rio Xingu and rio Tapajósbasins, Pará State, Brazil. The new species can be promptly distinguished fromits congeners by the combination of the following features: (I) temporal sensory
canal at sphenotic with two pores; (II) upper tooth plate of branchial arch withthree or four series of teeth; (III) area at the corner of the mouth, ventral to themaxillary barbel, with a small, roughly triangular fleshy flap, not forming anelongated barbel-like structure; (IV) contact between posterior process of theparieto-supraoccipital and nuchal plate; (V) dark stripe transversally crossing
the orbit, forming a mask-like blotch; (VI) absence of a distinct color patternalong midline of flank; (VII) dorsolateral body plates only with small, irregular,
rounded or vertically elongated dark brown or black blotches; ground color ofplates typically dusky but not forming large, conspicuous black patches; and(VIII) absence of a relatively large, conspicuous dark patch on anterior portionof dorsal fin.
Keywords: Corydoradinae, Corydoras sp. CW83, Jacareacanga, Taxonomy,
Volta Grande do Xingu.

Online version ISSN 1982-0224
Print version ISSN 1679-6225

Neotrop. Ichthyol.
vol. 22, no. 1, Maringá 2024

1 Departamento de Biologia e Zoologia, Instituto de Biociências, Universidade Federal de Mato Grosso, Avenida Fernando Corrêa
da Costa, 2367, Boa Esperança, 78060-900 Cuiabá, MT, Brazil. (LFCT) luiztencatt@hotmail.com (corresponding author).
2 Laboratório de Ictiologia de Altamira, Universidade Federal do Pará, Rua Coronel José Porfírio, 2515, São Sebastião, 68372-040
Altamira, PA, Brazil. (OLPC) ondina.couto@gmail.com, (LMS) lmsousa@ufpa.br.
3 Laboratório de Zoologia, Universidade Federal de Mato Grosso do Sul, Campus do Pantanal, Avenida Rio Branco, 1270,
Universitário, 79304-902 Corumbá, MS, Brazil. (SAS) sergio.pisces@gmail.com.

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A new Corydoras from the Xingu and Tapajós basins

Uma espécie nova de Corydoras é descrita das bacias do rio Xingu e do rio Tapajós,
Estado do Pará, Brasil. A espécie nova pode ser prontamente diferenciada desuas congêneres pela combinação das seguintes características: (I) canal sensorial
temporal no esfenótico com dois poros; (II) placa dentária superior do arco
branquial com três ou quatro séries de dentes; (III) área no canto da boca,
ventralmente ao barbilhão maxilar, com pequena aba carnosa algo triangular,
não formando uma estrutura alongada similar a um barbilhão; (IV) contato entreo processo posterior do parieto-supraoccipital e a placa nucal; (V) faixa escura
cruzando transversalmente a órbita, formando uma mancha em forma de máscara;(VI) ausência de um padrão de coloração distinto ao longo da linha mediana
do flanco; (VII) placas dorsolaterais do corpo apenas com manchas pequenas,
irregulares, arredondadas ou alongadas verticalmente, marrom-escuras ou pretas;
cor de fundo das placas tipicamente escura, mas não formando manchas pretas
grandes e conspícuas; e (VIII) ausência de uma mancha escura relativamente
grande e conspícua na porção anterior da nadadeira dorsal.
Palavras-chave: Corydoradinae, Corydoras sp. CW83, Jacareacanga, Taxonomia,
Volta Grande do Xingu.

INTRODUCTION
The Callichthyidae are Neotropical armored catfishes that can be promptly distinguishedfrom remaining Siluriformes by having two longitudinal series of dermal plates on flanks(Reis, 2003; Tencatt, 2022a). Currently, the family harbors more than 220 valid species,
from which about 180 are included in Corydoras Lacépède, 1803 (Fricke et al., 2023),
making it one of the most species-rich genera of Siluriformes (Tencatt et al., 2023).
Despite the comprehensive studies aiming to elucidate the taxonomy (e.g., Eigenmann,
Eigenmann, 1890; Ellis, 1913; Gosline, 1940; Nijssen, 1970; Nijssen, Isbrücker, 1967,
1980a, 1983, 1986) and phylogenetic relationships (e.g., Britto, 2003; Alexandrou et al.,2011) of the species within Corydoras, taxonomists just scratched the surface on thesefields of knowledge (Britto et al., 2007; Tencatt, Ohara, 2016a).
Corydoras is widely distributed within cis-Andean South America, with more thanhalf of its representatives occurring in the Amazon basin (Britto, 2003; Tencatt, Ohara,
2016b). One of the most iconic affluents of the rio Amazonas is the rio Xingu, withseveral new fish species being described in the last few years (e.g., Silva et al., 2020;
Tencatt et al., 2020; Costa et al., 2021; Garavello et al., 2021; Lehmann, Reis, 2021;
Oliveira et al., 2021; de Pinna, Dagosta, 2022; Neuhaus et al., 2022; Reis, Lehmann,
2022; Sabaj et al., 2022; Silva et al., 2022). Interestingly, a remarkably low number ofCorydoras species are formally known to occur in the rio Xingu basin, with C. benattii
Espíndola, Tencatt, Pupo, Villa‐Verde & Britto, 2018 and C. xinguensis Nijssen, 1972
as the only described representatives. The number of putative undescribed species
recognized by the fishkeeping hobby said to occur in the rio Xingu basin is also low,with only three morphotypes, Corydoras sp. C21, C87 and CW189 (see Tencatt, Evers(2016) for further information on the coding system in Corydoradinae), suggesting thatthe diversity of this genus in the rio Xingu basin is still poorly known.
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Another remarkable subdrainage forming the Amazon basin is the rio Tapajós system,with nearly 1,000 described fish species (Jézéquel et al., 2020). Currently, nine Corydoras
species are known to occur in this basin, namely: C. apiaka Espíndola, Spencer, Rocha& Britto, 2014, C. benattii, C. bifasciatus Nijssen, 1972, C. hephaestus Ohara, Tencatt &Britto, 2016, C. ornatus Nijssen & Isbrücker, 1976, C. rikbaktsa Lima & Britto, 2020,
C. hypnos Tencatt, Ohara, Sousa & Britto, 2022, C. thanatos Tencatt, Ohara, Sousa &Britto, 2022 and C. psamathos Tencatt, Ohara, Sousa & Britto, 2022 (Dagosta, de Pinna,
2019; Lima, Britto, 2020; Tencatt et al., 2022a). Contrasting with the rio Xingu basin,
the rio Tapajós basin currently has 27 coded species: C86, C133, C145, CW4, CW66,
CW83, CW101, CW102, CW127, CW135, CW155, CW156, CW162, CW167,
CW168, CW170, CW171, CW174, CW176, CW186, CW187, CW191, CW193,
CW194, CW195, CW196, and CW203, which highlight the gap between the numberof formally described species and the incoming of possible new species in the aquarium
hobby, as discussed by Tencatt et al. (2022a).
As noted above, the only Corydoras species currently known from both rio Xingu
and rio Tapajós basins is C. benattii. The analysis of Corydoras specimens from the rivers
Bacajá and Bacajaí plus smaller tributaries of the rio Xingu basin draining the regionof the Volta Grande do Xingu, revealed the presence of an undescribed new speciesof Corydoras fitting a coded species recorded from the rio Tapajós basin, Corydoras sp.
CW83. During the description process, the first author was able to collect specimensfrom the rio Tapajós basin in the region of Jacareacanga fitting in both morphology andcolor pattern the populations from the rio Xingu basin and, consequently, Corydoras
sp. CW83. Therefore, the aim of this study is to provide a formal description of thisundescribed species of Corydoras.
MATERIAL AND METHODS
Measurements were obtained using digital calipers to the nearest tenth of millimeter.
Morphometric and meristic data were taken following Tencatt et al. (2022b) and Reis
(1997), respectively. Morphometrics are reported as proportions of standard length (SL)or head length (HL). Terminology of barbels follows Britto, Lima (2003). Regarding
the orientation of the serrations on the posterior margins of the dorsal and pectoral
spines, the terminology is according to Ballen, de Pinna (2021). For the osteologicalanalysis, some specimens were cleared and stained (c&s) according to the protocol of
Taylor, Van Dyke (1985). Osteological terminology was based on Reis (1998), except
for the use of parieto-supraoccipital instead of supraoccipital (Arratia, Gayet, 1995),
pterotic-extrascapular instead of pterotic-supracleithrum (Slobodian, Pastana, 2018),
and scapulocoracoid instead of coracoid (Lundberg, 1970). Nomenclature of the laterosensory canals and preopercular pores are according to Schaefer, Aquino (2000) andSchaefer (1988), respectively. The supra-preopercle sensu Huysentruyt, Adriaens (2005)
was treated here as a part of the hyomandibula according to Vera-Alcaraz (2013). To
determine the development degree of the anterior laminar expansion of infraorbital
1 in relation to the nasal capsule, the specimen was positioned to maintain the largest
diameter of the nasal capsule horizontally. The width of frontal bone was obtainedat the same point as the least interorbital width. Vertebral counts include only freeni.bio.br | scielo.br/ni

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A new Corydoras from the Xingu and Tapajós basinscentra, with the compound caudal centrum (preural 1+ ural 1) counted as a single
element. The last two dorsal-fin rays were counted as distinct elements. Pharyngeal
teeth were counted in both sides of the branchial arches. Terminology regarding initialdevelopment follows Nakatani et al. (2001); the size of specimens in initial development
is exceptionally expressed in total length (TL).
Specimens from the rio Tapajós basin were regarded as non-types due the presenceof subtle morphological differences (presented in the Discussion section) in relation to
the specimens from the rio Xingu basin. In the description, numbers in parentheses
represent the total number of specimens with those counts. Numbers with an asterisk
refer to the counts of the holotype. Institutional abbreviations follow Sabaj (2020),
except for CITL, Coleção Ictiológica de Três Lagoas, Três Lagoas, Mato Grosso doSul, Brazil. Political geography data of the type material is presented in the following
order: country, state and municipality. The Extent of Occurrence of the new species
was estimated through the software GeoCAT (Geospacial Conservation Assessment
Tool; http://geocat.kew.org). The comparative material examined is the same as listed
in Tencatt et al. (2023).
RESULTS

Corydoras caramater, new species
urn:lsid:zoobank.org:act:55EEBC8C-5ED8-4FB3-A330-60474CEF52CD(Figs. 1-13, 16; Tab. 1)
Holotype. MNRJ 54621, 49.3 mm SL, Brazil, Pará, Senador José Porfírio, rio Bacajaí,
rio Xingu basin, 03°53’30”S 51°43’13”W, 11 Jul 2014, A. Gonçalves & D. Bastos.
Paratypes. All from Brazil, Pará, Senador José Porfírio, rio Xingu basin, except when
noted. CITL 929, 5 of 6, 35.7–45.3 mm SL, 1 of 6 c&s, 45.3 mm SL, rio Bacajaí,
03°41’20”S 51°45’08”W, 12 Jul 2014, A. Gonçalves & D. Bastos. CPUFMT 8150, 2,
35.2–40.7 mm SL, rio Bacajaí, 03°48’47”S 51°41’07”W, 9 Jul 2014, A. Gonçalves & D.
Bastos. INPA 60241, 3, 33.8–44.4 mm SL, rio Bacajaí, 03°49’02”S 51°41’04”W, 11 Jul
2014, A. Gonçalves & D. Bastos. MZUSP 129261, 4, 36.9–39.8 mm SL, rio Bacajaí,
03°39’22”S 51°45’40”W, 12 Jul 2014, A. Gonçalves & D. Bastos. LIA 148, 2, 39.9–44.0mm SL, rio Bacajaí, 03°36’19”S 51°46’05”W, 16 Oct 2013, A. Gonçalves. LIA 299,
4, 30.6–36.5 mm SL, 1 c&s, 39.1 mm SL, rio Bacajaí, 03°53’39”S 51°43’28”W, 11 Jul
2014, A. Gonçalves & D. Bastos. LIA 370, 3, 34.6–40.5 mm SL, rio Bacajaí, 03°50’23”S
51°40’42”W, 11 Jul 2014, A. Gonçalves & D. Bastos. LIA 530, 4, 28.6–39.8 mm SL,
rio Bacajaí, 03°41’56”S 51°44’23”W, 11 Jul 2014, A. Gonçalves & D. Bastos. LIA 672,
1, 27.2 mm SL, rio Bacajaí, 03°38’41”S 51°45’13”W, 12 Jul 2014, A. Gonçalves & D.
Bastos. LIA 864, 1, 36.5 mm SL, Vitória do Xingu, igarapé tributary of the rio Xingu,
03°19’29”S 51°47’20”W, 6 Oct 2014, D. Bastos & R. Oliveira. LIA 893, 2, 33.8–43.5mm SL, Vitória do Xingu, igarapé tributary of the rio Xingu, 03°15’57”S 51°43’50”W,
5 Oct 2014, D. Bastos & R. Oliveira. LIA 970, 2, 38.5–46.8 mm SL, Anapu, igarapé

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tributary of the rio Bacajá, 03°40’18”S 51°29’13”W, 3 Oct 2014, D. Bastos & R. Oliveira.
LIA 1073, 8, 34.3–43.0 mm SL, 2 c&s, 35.9–41.6 mm SL, Anapu, igarapé tributary of
the rio Bacajá, 03°40’18”S 51°29’13”W, 3 Oct 2014, D. Bastos & R. Oliveira. LIA
1996, 29, 30.1–44.8 mm SL, Vitória do Xingu, igarapé tributary of the rio Xingu,
03°15’57”S 51°43’50”W, 26 Jul 2014, D. Bastos & A. Martins. LIA 2257, 1, 43.7 mm
SL, Anapu, igarapé tributary of the rio Xingu, 03°05’12”S 51°38’04”W, 20 Jul 2014, D.
Bastos & A. Martins. LIA 3393, 2, 37.5–50.8 mm SL, Anapu, igarapé tributary of the rio
Xingu, 03°05’12”S 51°38’04”W, 1 Oct 2015, R. Oliveira. LIA 5416, 4, 39.9–46.4 mm
SL, Anapu, igarapé tributary of the rio Xingu, 03°05’12”S 51°38’04”W, 10 Jan 2015,
R. Oliveira. LIA 6511, 3, 36.9–41.3 mm SL, Anapu, igarapé tributary of the rio Xingu,
03°05’12”S 51°38’04”W, 26 Aug 2016, T. Bernardi and J. Arcanjo. LIA 8170, 1, 38.1mm SL, Anapu, igarapé Mosquito, 03°41’11”S 51°28’28”W, 7 Aug 2021, A. Ribeiro &P. Rocha. NUP 24841, 2, 29.3–44.6 mm SL, collected with the holotype.

FIGURE 1 | Corydoras caramater, holotype, MNRJ 54621, 49.3 mm SL, Senador José Porfírio, Pará, Brazil,
rio Bacajaí, rio Xingu basin.

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A new Corydoras from the Xingu and Tapajós basins

FIGURE 2 | Two preserved specimens of Corydoras caramater, showing general color and morphologicalpatterns in lateral view of (A) a paratype (LIA 8170, 38.1 mm SL), and (B) a non-type specimen from therio Tapajós basin (CPUFMT 8149, 1, 49.9 mm SL).

Non-type specimens. All from Brazil, Pará, Jacareacanga, ca. 06°12’S 57°45’W,
3–11 Jul 2023. CPUMT 8148, 13 of 14, 19.9–45.1 mm SL, 1 c&s of 14, 44.1 mm SL,
igarapé Limãozinho, M. A. Pinheiro, W. M. Ohara & L. F. C. Tencatt. CPUFMT 8149,
1, 49.9 mm SL, rio Pacu, local fishermen.
Diagnosis. Corydoras caramater can be distinguished from its congeners, except forthe species within the lineage 1 sensu Alexandrou et al. (2011), by the presence of thefollowing features: branch of the temporal sensory canal at sphenotic, which gives riseto the supraorbital canal, with two pores (vs. one pore); upper tooth plate of branchialarch with three or four series of teeth (vs. two series); and area at the corner of themouth, ventral to the maxillary barbel, with a small fleshy flap (vs. fleshy flap absent);
from the lineage 1 species, except for C. amapaensis Nijssen, 1972, C. blochi Nijssen,
1971, C. cortesi Castro, 1987, C. desana Lima & Sazima, 2017, C. pastazensis Weitzman,
1963, C. saramaccensis Nijssen, 1970, C. septentrionalis Gosline, 1940, C. serratus Sands,
1995, C. solox Nijssen & Isbrücker, 1983, and C. simulatus Weitzman & Nijssen, 1970,
by having a dark brown or black patch transversally crossing the orbit, forming a masklike blotch, which can be variably diffuse (vs. mask-like blotch absent); it differs from
C. cortesi, C. desana, C. pastazensis, C. septentrionalis, and C. simulatus by the absence ofa distinct color pattern along midline of flank (vs. midline of flank with moderate- tolarge-sized, conspicuous dark brown or black blotches in C. desana, C. pastazensis, C.
septentrionalis, and C. simulatus; with a longitudinal dark brown or black stripe in C.
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cortesi); from C. amapaensis, C. serratus and C. solox, it differs by having dorsolateral bodyplates only with small, irregular, rounded or vertically elongated dark brown or black
blotches; ground color of plates typically dusky but not forming large, conspicuous
black patches (vs. midventral portion of dorsolateral body plates on region between
middle portion of dorsal fin and caudal-fin base typically with large, conspicuous darkbrown or black longitudinally elongated blotch or stripe; dark stripe variably diffuse,in C. amapaensis; wide, dark brown or black longitudinal stripe from predorsal region
to caudal-fin base or, alternatively, dorsolateral body plates around anterior portion of
dorsal-fin base with dark brown or black patch in C. serratus; region between anterior
portion of dorsal fin and caudal-fin base with wide, longitudinal dark brown or black
stripe in C. solox); from C. blochi and C. saramaccensis by the absence of a relatively
large, conspicuous dark patch on anterior portion of dorsal fin (vs. anterior portion of
dorsal fin with a conspicuous concentration of dark brown or black chromatophores,
forming a relatively large, conspicuous patch). Additionally, Corydoras caramater can be
distinguished from C. geoffroy Lacépède, 1803, C. amapaensis, C. septentrionalis, and C.
solox by having a triangular fleshy flap at the corner of mouth, ventrally to maxillarybarbel, not forming an elongated barbel-like structure (vs. fleshy flap at corner of mouth
elongated, forming a barbel-like structure).
Description. Morphometric data in Tab. 1. Head laterally compressed with acutely
convex dorsal profile, roughly triangular in dorsal view. Snout well developed, conical;
conspicuously pointed in some specimens. Head profile slightly concave from tip ofsnout to anterior nares; nearly straight in some specimens; ascending nearly straight orslightly 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, concave from this point to caudal-finbase. Ventral profile of body nearly straight 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 concave until caudal-fin base.
Body roughly elliptical in cross section at pectoral girdle, gradually becoming morecompressed toward caudal fin. Highest body depth at vertical through anterior originof dorsal fin.
Eye rounded, located dorsolaterally on head. Orbit delimited anteriorly by lateral
ethmoid, anterodorsally by frontal, posterodorsally by sphenotic, posteroventrally byinfraorbital 2, and anteroventrally by infraorbital 1 (Figs. 3, 4A). Anterior and posteriornares close to each other, only separated by flap of skin. Anterior naris tubular. Posteriornaris close to anterodorsal margin of orbit, separated from it by distance similar to naris
diameter. Mouth small, subterminal, width similar to bony orbit diameter. Maxillarybarbel typically well developed, slightly surpassing anteroventral limit of gill opening;ranging from poorly developed, distant from anteroventral limit of gill opening, tomoderately developed, nearly reaching anteroventral limit of gill opening in somespecimens; base of barbel with fleshy flap on its dorsolateral portion (Fig. 5). Outermental barbel with similar size or slightly longer than maxillary barbel. Inner mental
barbel fleshy, base of each counterpart slightly separated from each other. Area at mouthcorner, ventral to maxillary barbel, with small, roughly triangular fleshy flap (Fig. 5).
Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout
and isthmus.
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TABLE 1 | Morphometric data of the holotype and 17 paratypes of Corydoras caramater. SD = Standard
deviation.
Holotype

Low–High

Mean±SD

49.3

29.3–49.3

39.5±4.9

Depth of body

38.7

35.2–38.7

36.9±1.0

Predorsal distance

52.3

49.4–53.8

51.9±1.1

Prepelvic distance

49.1

48.2–51.8

50.0±0.9

Preanal distance

81.9

78.0–82.6

80.4±1.1

Preadipose distance

85.4

79.5–86.2

83.8±1.5

Length of dorsal spine

22.1

19.8–23.6

21.4±1.0

Length of pectoral spine

23.1

15.7–23.9

22.0±1.7

Standard length (mm)Percentage of standard length

Length of adipose-fin spine

9.1

8.2–10.2

9.2±0.6

Depth of caudal peduncle

15.2

13.9–16.5

15.3±0.6

Length of dorsal-fin base

19.3

16.3–19.3

17.9±0.8

Dorsal to adipose distance

19.1

15.7–20.3

18.0±1.1

Maximum cleithral width

26.2

23.5–26.2

25.0±0.7

Head length

44.6

42.4–47.3

45.2±1.3

Length of maxillary barbel

15.6

11.6–20.1

17.8±2.0

Head depth

80.5

73.7–80.5

76.0±1.9

Least interorbital distance

25.0

21.9–25.1

23.4±0.8

Horizontal orbit diameter

19.1

19.1–24.1

21.1±1.4

Snout length

46.8

44.2–49.2

46.7±1.5

Least internarial distance

13.2

10.5–13.6

11.9±0.9

Percentage of head length

FIGURE 3 | Head osteological pattern in a c&s
paratype of Corydoras caramater (LIA 1073, 41.6 mm
SL), showing general morphology in lateral view.
Abbreviations: f: frontal, fdbp: first dorsolateralbody plate, io1–2: infraorbital 1 and 2, iop:interopercle, n: nasal, op: opercle, pes: pteroticextrascapular, pop: preopercle, prh: posterodorsal
ridge of hyomandibula, pso: parieto-supraoccipital,
sph: sphenotic. Additional pore of the temporal
sensory canal at sphenotic outlined in yellow. Scalebar = 1 mm.

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FIGURE 4 | Details on cranium osteological pattern in a c&s paratype of Corydoras caramater (LIA 1073,
35.9 mm SL), showing general morphology of (A) lateral ethmoid in lateral view, and of (B) mesethmoid
in dorsal view. Abbreviations: f: frontal, le: lateral ethmoid, n: nasal, pes: pterotic-extrascapular, pso:parieto-supraoccipital, sph: sphenotic. Additional pore of the temporal sensory canal at sphenotic
outlined in yellow. Area where the illustrated bones are located in fish’s body marked in red in theminiature drawing of the new species. Scale bars = 1 mm.

FIGURE 5 | Tip of snout in a paratype of Corydoras caramater (CITL 929, 45.3 mm SL), showing thearea at corner of mouth in lateral view. Red arrow indicates the roughly triangular fleshy flap locatedbetween maxillary barbel and anteroventral portion of snout tip; yellow arrow indicates fleshy flap on
dorsolateral portion of maxillary barbel base. Area where the illustrated structures are located in fish’s
body marked in red in the miniature drawing of the new species. Scale bar = 1 mm.

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Mesethmoid long; anterior tip well developed, larger than 50% of bone length;
posterior portion relatively narrow, entirely covered by thick layer of skin; posterior
portion slightly narrower in specimen CPUMT 8148, 44.1 mm SL (Figs. 4B, 6).
Nasal capsule typically delimited anterodorsally by mesethmoid, posterodorsally byfrontal, and ventrally by lateral ethmoid; nasal capsule delimited dorsally by frontal
and ventrally by lateral ethmoid in specimen CPUMT 8148, 44.1 mm SL. Nasal
slender, laterally curved, inner margin with poorly- to moderately-developed laminar
expansion, typically contacting only frontal; outer margin with poorly-developed
laminar expansion, not contacting lateral ethmoid; strongly reduced laminar expansion
in some specimens (Figs. 3, 4, 6). Lateral ethmoid deep in lateral view, conspicuously
expanded anteriorly, with anterodorsal expansion contacting only mesethmoid, andanteroventral expansion connected to lateroventral process of mesethmoid; anterodorsal
expansion contacting mesethmoid and frontal in CPUMT 8148, 44.1 mm SL (Fig. 3A).
Frontal elongated, narrow, width less than half of entire length; anterior projection
relatively short, size generally smaller than nasal length; moderately developed insome specimens, with size similar to nasal length; anterior projection long, with size
larger than nasal length in specimen CPUMT 8148, 44.1 mm SL. Frontal fontanel
large, slender, and somewhat ellipsoid; posterior tip extension clearly surpassing
anterior margin of parieto-supraoccipital (Figs. 3, 6). Sphenotic somewhat trapezoid,
contacting parieto-supraoccipital dorsally, pterotic-extrascapular posteriorly, second
infraorbital posteroventrally and frontal anteriorly (Figs. 3, 6). Pterotic-extrascapularroughly pipe-shaped, with posterodorsal portion contacting first lateral-line ossicle,
posteroventral margin contacting cleithrum, and anteroventral margin contacting

FIGURE 6 | Top of head and predorsal region of trunk of a c&s paratype of Corydoras caramater (LIA
1073, 41.6 mm SL) in dorsal view. Abbreviations: f: frontal, fdbp: first dorsolateral body plate, n: nasal, np:
nuchal plate, pes: pterotic-extrascapular, pso: parieto-supraoccipital, sph: sphenotic. Scale bar = 1 mm.

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opercle and infraorbital 2; posterodorsal expansion almost entirely covering lateral
opening of swimbladder capsule, leaving slender area on its dorsal margin covered onlyby thick layer of skin (Figs. 3, 6). Parieto-supraoccipital wide, posterior process longand contacting nuchal plate; region of contact between posterior process and nuchal
plate covered by thick layer of skin (Fig. 6).
Two laminar infraorbitals with minute odontodes. Infraorbital 1 large, ventral
laminar expansion ranging from moderately to well developed; anterior portion withlaminar expansion ranging from moderately developed, slightly surpassing middle
portion of nasal capsule, to well-developed, reaching anterior margin of nasal capsule;
inner laminar expansion strongly reduced (Figs. 3, 6, 7A). Infraorbital 2 small, widened
dorsally, with posterior laminar expansion ranging from moderately to well developed;
posteroventral margin contacting posterodorsal ridge of hyomandibula, posterodorsaledge contacting sphenotic and pterotic-extrascapular; inner laminar expansion strongly
reduced (Figs. 3, 6, 7B). Posterodorsal ridge of hyomandibula close to its articulation
with opercle slender, exposed, and bearing small odontodes (Figs. 3, 7C). Dorsal ridgeof hyomandibula between pterotic-extrascapular and opercle entirely or almost entirely

FIGURE 7 | Infraorbital series in lateral (A) and dorsal (B) views, and (C) suspensorium plus operculumin lateral view of a c&s paratype of Corydoras caramater (LIA 1073, 35.9 mm SL). Abbreviations: aa:angulo-articular, d: dentary, hym: hyomandibula, io1–2: infraorbital 1 and 2, iop: interopercle, mp:
metapterygoid, op: opercle, pop: preopercle, prh: posterodorsal ridge of hyomandibula, q: quadrate. Red
arrows indicate the inner laminar expansions of both infraorbitals. Area where the illustrated bones
are located in fish’s body marked in red in the miniature drawing of the new species. Scale bars = 1 mm.

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A new Corydoras from the Xingu and Tapajós basinscovered by posterodorsal portion of infraorbital 2; entirely covered by thick layer of skinin some specimens. Interopercle partially covered by thick layer of skin, with posterior
portion exposed and bearing odontodes; subtriangular, anterior projection moderately
developed (Figs. 3, 7C). Preopercle elongated, relatively slender; minute odontodes on
external surface (Figs. 3, 7C). Opercle dorsoventrally elongated, width slightly smaller
than half of its entire length; free margin convex, posterodorsal portion with smoothly
concave area in some specimens; without serrations and covered by small odontodes(Figs. 3, 7C).
Four branchiostegal rays decreasing in size posteriorly. Hypobranchial 1 deep, withmesial expansion poorly to well ossified; hypobranchial 2 somewhat triangular, tip
ossified and directed towards anterior portion, posterior margin cartilaginous; ossified
portion ranging from strongly reduced to poorly developed, with cartilaginous portion
at least twice of its size in smaller specimens (LIA 299, 39.1 mm SL; LIA 1073, 35.9–41.6mm SL) (Fig. 8A); ossified portion well developed in larger specimens (CPUMT 8148,
44.1 mm SL; CITL 929, 45.3 mm SL), around twice size of cartilaginous portion (Fig.
8C). Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1with strongly reduced process on anterior margin of mesial portion; ceratobranchial 3
with continuous laminar expansion on postero-lateral margin; ceratobranchial 5 toothed

FIGURE 8 | Hyoid and branchial arches in (A) a c&s paratype of Corydoras caramater (LIA 1073, 35.9 mmSL), showing its general morphology in dorsal view, with the detail of hypobranchial (hb) 1 and 2, and of(B) upper tooth plate plus pharyngobranchials ( (pb3 and 4) 3 and 4). General morphology in dorsal viewof both hypobranchials (1 and 2) of another c&s paratype (CITL 929, 45.3 mm SL). Area highlighted in
red in (A) indicating the position of upper tooth plate plus pharyngobranchials in the branchial basket.
Scale bars = 1 mm.

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on posterodorsal surface, with 28 to 31(4) teeth aligned in one row. Four epibranchials
with similar size; epibranchial 2 slightly larger than others, with small pointed process onlaminar expansion of posterior margin; epibranchial 3 with roughly triangular uncinate
process on laminar expansion of posterior margin; process variably bent mesially. Two
wide pharyngobranchials (3 and 4); pharyngobranchial 3 with roughly triangularlaminar expansion on posterior margin; expansion typically notched. Upper tooth plateroughly oval, 46 to 60(4) teeth aligned in three or four rows on posteroventral surface;rows slightly apart from each other (Fig. 8B).
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
close to 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, with one and two
pores, respectively. Supraorbital canal branched, running through nasal bone. Epiphyseal
branch relatively long; pore opening close to frontal fontanel. Nasal canal with three
openings, first on posterior edge, second on posterolateral portion and typically fusedwith first pore, and third on anterior edge; second opening variably absent. Infraorbital
canal running through entire infraorbital 2, extending to infraorbital 1 and opening
into two or three pores. Preoperculomandibular branch giving rise to preoperculomandibular canal, which runs through entire preopercle with three openings, leading
to pores 3, 4, and 5, respectively; pore 3 opening at posterodorsal ridge of hyomandibula
in some specimens.
Dorsal fin subtriangular, located just posterior to second or third dorsolateral bodyplate. Dorsal-fin rays II,7(1), II,7,i(1), II,8*(16), posterior margin of dorsal-fin spine withfour to 11 strongly reduced to poorly-developed serrations, perpendicularly directedor antrorse; serrations restricted to distal half of spine; small odontodes on anterior andlateral surfaces of spine (Fig. 9A). Nuchal plate well developed, almost entirely exposed,with minute odontodes. Spinelet short; spine well developed, with adpressed distal tip
reaching or slightly surpassing posterior origin of dorsal-fin base. Pectoral fin roughly
triangular, its origin just posterior to gill opening. Pectoral-fin rays I,9,i(2), I,10*(11),I,10,i(3), I,11(2), posterior margin of pectoral spine with 13 to 19 conical serrations
along almost its entire length, absent around origin of spine; most serrations welldeveloped and retrorse; serrations close to origin of spine conspicuously less developed;
some serrations variably perpendicularly directed; small odontodes on anterior, dorsal
and ventral surfaces of spine (Fig. 9B). Anteroventral portion of cleithrum exposed;
posterolateral portion of scapulocoracoid moderately developed, exposed, with anterior
portion slightly expanded anteriorly, not in contact with anteroventral portion ofcleithrum. Opening of axillary gland sensu Kiehl et al. (2006) apparently reduced tonarrow slit just posterior to pectoral-fin spine base.
Pelvic fin oblong, located just below second or third ventrolateral body plate, andat vertical through second or third dorsal-fin branched rays. Pelvic-fin rays i,5*(18).
Anterior internal process of basipterygium well developed and conspicuously laterally
expanded, with nearly vertically placed dorsal lamina; anterior external process laminar,
well developed, slightly to moderately expanded posteriorly; dorsal ischiac process

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FIGURE 9 | Lateral view of (A) the dorsal-fin spine and dorsal view of (B) the left pectoral-fin spine ina c&s paratype of Corydoras caramater (LIA 1073, 41.6 mm SL), showing their serration patterns. Area
where the illustrated bones are located in fish’s body marked in red in the miniature drawing of the new
species. Scale bars = 1 mm.

well developed, with anterior laminar expansion moderately expanded anteriorly, andposterior laminar expansion slightly to moderately expanded posteriorly; anterior andposterior laminar expansions of ischiac process roughly triangular or rounded; ventral
ischiac process clearly smaller than dorsal process, roughly triangular, bent anteriorly(Fig. 10). Adipose fin roughly triangular, separated from base of last dorsal-fin ray by six
or seven dorsolateral body plates. Anal fin subtriangular, located just posterior to 12th or
13th ventrolateral body plates, and at vertical through adipose-fin spine base or region of
adipose-fin membrane. Anal-fin rays ii,5,i(3), ii,6*(15). Caudal fin bilobed, with dorsal
lobe typically larger than ventral lobe; some specimens with dorsal lobe clearly smaller
than ventral lobe, apparently by undergoing regeneration. Caudal-fin rays i,12,i*(18),with four or five dorsal and ventral procurrent rays; small cartilage between upper
principal and procurrent caudal-fin rays (presumably opisthural cartilage (Monod,
1968; McDowall, 1999)) (Fig. 11).

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FIGURE 10 | Pelvic girdle in a c&s paratype of Corydoras caramater (LIA 1073, 35.9 mm SL). Abbreviations:bp: basipterygium, pae: anterior external process, pai: anterior internal process, pi: dorsal ischiac
process. Area where the illustrated bones are located in fish’s body marked in red in the miniaturedrawing of the new species. Left dorsal ischiac process damaged during dissection. Scale bar = 1 mm.

Four to six laterosensory canals on trunk; first ossicle tubular, second ossicle laminar,
third, fourth, fifth and sixth lateral-line canals, if present, encased in third, fourth, fifthand sixth dorsolateral body plates, respectively. Body plates with minute odontodes
scattered over exposed area, with conspicuous line of odontodes confined to posterior
margins. Dorsolateral body plates 25(16), 26*(2). Ventrolateral body plates 22(16),23*(2). Dorsolateral body plates along dorsal-fin base 6*(9), 7(9). Dorsolateral bodyplates between adipose- and caudal-fin 8(3), 9(14), 10*(1). Preadipose platelets 3(1),4(15), 5*(2). Ventral surface of trunk between posteroventral margin of cleithrum
and pelvic-fin origin laterally delimited by first and second ventrolateral body plates;
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 portionof caudal peduncle. Anterior margin of orbit, above region of junction between frontal
and lateral ethmoid, ventral and anterodorsal margins of nasal capsule, lateral surface ofni.bio.br | scielo.br/ni

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FIGURE 11 | General morphology of caudal skeleton in a c&s paratype of Corydoras caramater (LIA 1073,
41.6 mm SL), showing the small cartilage (black dotted line) between upper principal and procurrent
caudal-fin rays. Abbreviations: ccc: compound caudal centrum, cfr: caudal-fin principal rays, dpcr:
dorsal procurrent rays, epu: epural, has: haemal spine, hyp 1–5: hypurals 1 to 5, nes: neural spine, par:parhypural, pu 2–4: preural centra 2 to 4, un: uroneural, vpcr: ventral procurrent rays. Area where theillustrated bones are located in fish’s body marked in red in the miniature drawing of the new species.
Scale bar = 1 mm.

head below infraorbital 1, and lateral and dorsal portions of snout with numerous small
platelets bearing odontodes; region around tip of snout typically devoid of platelets;
region around nasal capsule and dorsal and lateral surfaces of snout with few platelets
in specimen (CPUMT 8148, 44.1 mm SL). Ventral surface of head and trunk withsmall irregular platelets bearing odontodes; ventral surface of head variably lacking
platelets on its anterior portion, with more numerous and concentrated platelets on its
posterior portion, becoming gradually fewer and sparser towards posterior portion oftrunk; mesial portion of ventral surface of trunk close pelvic fins and/or region aroundpectoral-fin origin with concentration of platelets in some specimens.
Vertebral count 22(1), 23(3); ribs 5(4); first pair conspicuously large, its middle portion
closely connected to first ventrolateral body plate; its tip not connected to anterior
external process of basipterygium. Parapophysis of complex vertebra well developed.

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Coloration in alcohol. Overall color pattern of body in Figs. 1–2. Ground colorof body pale- to brownish yellow or beige. Top of head dark brown. Dorsal andlateral surface of head, and lateral surface of cleithrum covered by dark brown or black
chromatophores, not forming small blotches; elongated dark patch transversally crossing
orbit, forming typical mask-like blotch, which is generally diffuse. Dorsolateral bodyplates with conspicuous concentration of dark brown or black chromatophores, forming
small, irregular, rounded or vertically elongated dark brown or black blotches, which areroughly transversally aligned on plates; series of blotches on middle or posterior portionof dorsolateral body plates. Ventrolateral body plates with conspicuous concentrationof dark brown or black chromatophores, forming small, irregular, rounded or verticallyelongated dark brown or black blotches, which are roughly transversally aligned onplates; series of blotches typically restrict to dorsal half of ventrolateral body plates andplaced on its middle portion. Blotches on lateral body plates more evident on anterior
portion of trunk; posterior margin of body plates typically with dark brown or black
chromatophores, forming thin dark lines along border of plates. Dorsal-fin with darkbrown or black chromatophores, more concentrated on spine and rays, and typicallyforming small, diffuse dark blotches, which are roughly longitudinally or obliquelyaligned. Pectoral and pelvic fins with dark brown or black chromatophores, not forming
dark blotches; pelvic fin with scarce chromatophores in some specimens. Adipose finwith conspicuous concentrations of dark brown or black chromatophores, typicallyforming small, diffuse dark blotches, especially on its spine. Anal fin with dark brown or
black chromatophores, which are more concentrated on rays, typically forming small,diffuse dark blotches roughly aligned transversally; blotches generally more evident on
middle portion of fin. Caudal fin with conspicuous concentrations of dark brown or
black chromatophores, mostly on rays, forming numerous, small, diffuse dark blotches,
which are roughly aligned transversally; in some specimens, caudal-fin blotches slightly
more evident than blotches in remaining fins.
Coloration in life. Similar to color pattern of preserved specimens, but with lightyellowish orange ground color of body, especially on anterodorsal portion of trunk.
Mask-like blotch variably more evident. Body covered by greenish yellow iridescentcoloration (Figs. 12, 13).
Sexual dimorphism. As well-documented in Corydoradinae (see Britto, 2003;
Nijssen, Isbrücker, 1980b; Spadella et al., 2017), male specimens of C. caramater present
a genital papilla, which is somewhat tubular in shape.
Geographical distribution. Corydoras caramater is currently known from the basinsof the rivers Bacajá and Bacajaí and other small tributaries of the right margin of the rio
Xingu draining the region of the Volta Grande do Xingu, and also from tributaries of
the rio Tapajós basin in the region of Jacareacanga, Pará State, Brazil (Fig. 14).
Ecological notes. In both rivers Xingu and Tapajós basins, C. caramater was captured
from small streams to the main channel of smaller rivers (Fig. 15). In the igarapéLimãozinho (LFCT, pers. obs.), a tributary of the rio Tapajós basin, the new species
was mostly observed in shallow sites (up to about 30 cm deep), with width ranging

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FIGURE 12 | Uncatalogued aquarium specimens of Corydoras caramater from the rio Tapajós basin
photographed alive, showing general color pattern and morphology of a male (A) and of a female (B)specimens. Photos by Hans Evers.

from 1 to 3 m, slow to moderate water current, and substrate mostly composed byfine sand and gravel, with areas of leaf litter and submerged branches/logs, as well as
aquatic macrophytes. In this same site, the new species was observed shoaling together
with two undescribed mimetic congeners (see Alexandrou et al. (2011) for a broader
discussion on mimicry in Corydoradinae), Corydoras sp. CW101 (less abundant) and
CW102 (most abundant), with the new species occurring in intermediate abundance
when compared to both of them. Additionally, the new species was also captured withanother undescribed congener in the igarapé Limãozinho, Corydoras sp. CW193. The
new species was observed in the igarapé Sonrizal (Fig. 15C), rio Tapajós basin, in asimilar habitat as described for the igarapé Limãozinho, except for its larger width(about 10 m) and depth (about 1.5 m). In the igarapé Sonrizal, the new species wasobserved in syntopy with the following congeners: Corydoras sp. C151, C152, CW66,
CW174, and CW176. Similarly to the observed in the igarapé Limãozinho, C. caramater
was found in syntopy with Corydoras sp. CW101 and CW102.

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FIGURE 13 | Specimens of Corydoras caramater from the rio Tapajós basin photographed alive in lateralview, showing general color pattern and morphology of (A) an uncatalogued specimen from the rio Pacu
with paler background color of body, (B) an uncatalogued specimen from igarapé Sonrisal with slightly
darker background color of body, and (C) a non-type specimen (CPUFMT 8149, 1, 49.9 mm SL) from therio Pacu with clearly darker background color of body. Photos by William Ohara.

Etymology. The specific epithet caramater is formed by the junction of two words
derived from the Latin ‘cara’, which means dear, beloved, and ‘mater’, meaning mother.
This is a small tribute to these strong women, who work hard and are still responsible,
often alone, for tenderly raising their children. The name especially honors Miriam
Tencatt, Jéssica Mendonça (mother and wife of LCFT, respectively), Ireide da Silva
Pinto (mother of OLPC), Vanda Santos (in memorian), Roberta Murta-Fonseca (motherand wife of SAS, respectively), and Edina Melo de Sousa (mother of LMS), but extends
to all caring mothers around the world. A noun in apposition.
Conservation status. Corydoras caramater is currently known from the Bacajá andBacajaí river basins and other small tributaries of the right margin of the rio Xingu
draining to Volta Grande do Xingu, plus tributaries of the rio Tapajós basin in theregion of Jacareacanga, all in Pará, Brazil. Considering the type-locality region (rioBacajaí), the negative effects to the ichthyofauna caused by the implementation of
the Belo Monte hydroelectric complex must be closely monitored (see Keppeler etal., 2022). Regarding the rio Tapajós basin population, the region of Jacareacanga is

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FIGURE 14 | Map showing the geographical distribution of Corydoras caramater in the rio Xingu basin (purple star: type-locality; whitediamonds additional records), and in the rio Tapajós basin (yellow dot). Each symbol may represent more than one locality.

widely known by its intense gold-mining activities, which are often illegal, causing awide range of negative impacts on nature (see de Bakker et al., 2021; Bandeira Junior,
Carvalho, 2023). Although such negative impacts are known and worrying, there
is no available evidence that they constitute a threat to the new species as a whole.
Additionally, considering our findings, the Extent of Occurrence (EOO) was estimatedat about 30.000 km2, which represents a relatively large area. Therefore, according to
the International Union for Conservation of Nature (IUCN) categories and criteria(IUCN Standards and Petitions Subcommittee, 2022), Corydoras caramater would beclassified as Least Concern (LC).
Remarks. Corydoras caramater was bred under aquarium conditions by Hans Evers,
who documented its ontogenetic development from 8.0 mm to 24.0 mm TL, showing
general changes in external morphology and color pattern (Fig. 16). Specimen with 8.0
mm TL in early flexion stage (Fig. 16A) presents head slightly depressed, with shortand conspicuously rounded snout; barbels relatively short and with well-developed
papillae, which will gradually become less developed along individual’s growth; eyelarge; median fin fold present, extending from post-cephalic region to genital opening;caudal-fin rays distinct, fin not detached from fin fold; dorsal, anal, pelvic and adipose
fins not distinct; caudal-fin asymmetrical, dorsal portion distinctly longer than ventral;
pectoral fin roughly rounded; body plates absent; dark brown or black chromatophores
conspicuously more concentrated on anterior portion of trunk, forming a large dark
patch; body covered by greenish yellow iridescent coloration.
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FIGURE 15 | Collecting sites of Corydoras caramater, showing (A) the rio Bacajaí, (B) a small stream
tributary of the rio Bacajá, both draining to the rio Xingu, and (C) the igarapé Sonrisal, a tributary of the
rio Tapajós basin, all in Pará State, Brazil.

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FIGURE 16 | Ontogenetic series of Corydoras caramater (bred under aquarium conditions) showing
general changes in external morphology and color pattern in specimens with (A) 8.0 mm TL, (B) 10.0
mm TL; (C) 13.0 mm TL, (D) 16.0 mm TL, (E) 19.0 mm TL, and (F) 24.0 mm TL. Photos by Hans Evers.

Specimen with 10.0 mm TL in early post-flexion stage (Fig. 16B) displays slightly
more pronounced snout, clearly more developed barbels, and reduction of median fold,with dorsal and caudal fins partially distinct; hypural plates visible by transparency;
dorsal-fin rays distinct; pectoral fin slightly more developed; pelvic-fin fold partiallydetached; anal and adipose fins indistinct; slightly more pigmented body, withlongitudinal series of diffuse dark blotches along midline of flank. Specimens with
13.0 and 16.0 mm TL, respectively, in early juvenile stage (Figs. 16C, D), showing thegradual development of snout, which becomes more pronounced and pointed along

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individual’s growth; complete absorption of median fold; pelvic, adipose and anal finsdistinct; caudal fin bilobed, with ventral lobe clearly less developed than dorsal lobe;
beginning of formation of lateral body plates; body gradually more pigmented, with
continuous reduction of dark patch on anterior portion of trunk; roughly longitudinal
series of diffuse dark blotches along dorsal and ventral portions of flanks; oblique dark
stripe from anteroventral margin of orbit to upper lip lateral area, which is initiallydiffuse, turning more evident afterwards, and then gradually vanishing along individual’s
growth; caudal fin with somewhat transversal slender dark bars, gradually becoming
more defined.
Juvenile specimen with 19.0 mm TL (Fig. 16E) with more developed lateral bonyplates; caudal-fin ventral lobe well developed; body densely covered by dark brownor black chromatophores, forming small irregular dark blotches; longitudinal series of
blotches on flanks diffuse. Color pattern and general external morphology of juvenile
specimen with 24 mm TL (Fig. 16F) similar to fully growth specimens, but with slenderbody and slightly more diffuse coloration.

DISCUSSION
The analysis of smaller c&s paratypes (LIA 299, 1 c&s, 39.1 mm SL; LIA 1073, 2 c&s,
35.9–41.6 mm SL) revealed the presence of poorly ossified hypobranquial 1 and 2,
an uncommon feature among Corydoradinae (Fig. 8A). Currently, a poorly ossified
hypobranchial 2 is only reported for C. difluviatilis Britto & Castro, 2002, from which
the new species differs by having the following features: (I) branch of the temporal
sensory canal at sphenotic, which gives rise to the supraorbital canal, with two pores(vs. one pore); (II) upper tooth plate of branchial arch with three or four series of teeth(vs. two series); (III) corner of the mouth, ventral to the maxillary barbel, with a small
fleshy flap (vs. fleshy flap absent); (IV) contact between posterior process of the parietosupraoccipital and nuchal plate (vs. absence of contact between these structures); (V) adark brown or black patch transversally crossing the orbit, forming a mask-like blotch,
which can be variably diffuse (vs. mask-like blotch absent); and (VI) posterior margin of
pectoral-fin spine with serrations along almost its entire length, absent around origin ofspine (vs. serrations restricted to proximal half of the spine).
Despite the presence of such uncommon feature in smaller adult specimens (up to
about 42.0 mm SL), larger adult specimens (CPUMT 8148, 1 c&s, 44.1 mm SL; CITL
929, 1 c&s, 45.3 mm SL) display both hypobranquial 1 and 2 with well-developed
ossified portion (Fig. 8C), which is the most common condition within Corydoradinae(see Britto, 2003). Despite being ontogenetic variable, the presence of poorly-ossified
hypobranquials in adult specimens was not observed in any other congener besides C.
difluviatilis. Although rare and potentially informative at the phylogenetic level, thisfeature should be avoided for diagnostic purposes considering its variability. In any case,
it is important to emphasize that such variability was only observed when comparing
individuals from different sizes and not from different basins (i.e., Xingu and Tapajósbasins).

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The available distribution records of C. caramater show a disjunct geographicaloccurrence, with relatively distant records from tributaries of the right bank of the
rio Xingu and from tributaries of the rio Tapajós basin, region of Jacareacanga, Pará.
Interestingly, the known geographic distribution of the new species resembles that of C.
benattii, although more restricted. Similarly, other species were also described from bothbasins, such as: Ancistrus luzia Neuhaus, Britto, Birindelli & Sousa, 2022, Archolaemus
janeae Vari, de Santana & Wosiacki, 2012, Hopliancistrus munduruku Oliveira, Zuanon,
Rapp Py-Daniel, Birindelli & Sousa, 2021, Leptodoras oyakawai Birindelli, Sousa & Sabaj
Pérez, 2008, Moenkhausia pirauba Zanata, Birindelli & Moreira, 2010, Schizodon trivittatus
Garavello, Ramirez, Oliveira, Britski, Birindelli & Galetti, 2021, and Spatuloricaria tuira
Fichberg, Oyakawa & de Pinna, 2014. Nevertheless, the absence of C. caramater in thetributaries of the left margin of the rio Xingu may be caused by the lack of a speciesoriented sampling, and future efforts in the region should be made to address this issue.
Comparing the specimens from these two basins showed that both morphologic andcolor patterns are overall compatible (see Fig. 2), which made it impossible to provide
a solid diagnosis separating the two populations into distinct species. The only putative
diagnostic features raised herein are related to the morphology of the mesethmoid andlateral ethmoid, which slightly changes nasal capsule morphology, as pointed in the
Description section (see exceptional cases related to specimen CPUMT 8148, 44.1 mm
SL). Therefore, based only on the subtle differences in the morphology of these twobones, it seems premature to consider these two populations as two distinct species.
As aforementioned, specimens of C. caramater from the rio Tapajós basin were observed
shoaling together with two congeners sharing similar color pattern, Corydoras sp.
CW101 and CW102. Despite that, these species present clearly different morphologicalpattern. The presence of syntopic species sharing similar color pattern but having 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., 2013, 2019, 2021,
2022a; Lima, Sazima, 2017; Tencatt, Britto, 2016; Tencatt, Ohara, 2016a,b; Tencatt,
Pavanelli, 2015). Corydoras caramater can be distinguished from both coded species by
having the three main diagnostic features of the lineage 1 species sensu Alexandrou et al.
(2011) (i.e., features (I), (II) and (III) presented in the first paragraph of this section). The
new species can be further distinguished from Corydoras sp. CW101 by lacking retrorse
laminar serrations along posterior margin of dorsal-fin spine (vs. presence of retrorse
laminar serrations); and from CW102 by having the posterior margin of the pectoralfin spine with most serrations retrorse (vs. most serrations antrorse).
The molecular-based phylogenetic hypothesis of Alexandrou et al. (2011) recovered
nine lineages of species within Corydoradinae, with lineage 2 composed by Aspidoras
Ihering, 1907, lineage 3 by Scleromystax Günther, 1864, and lineages 1, 4, 5, 6, 7, 8
and 9 harboring the species within Corydoras. In the last decade, this work provided
a valuable support for articles on systematics of the group, with the lineage system
working as a “shortcut” in many species diagnoses (e.g., Tencatt et al., 2013, 2016; 2019,2020, 2021, 2022a, 2023; Tencatt, Pavanelli, 2015; Tencatt, Britto, 2016; Tencatt, Evers,
2016; Tencatt, Ohara, 2016a,b; Bono et al., 2019; Bentley et al., 2021). Regardless of the
major advance provided by the work of Alexandrou et al. (2011), their results could not
be entirely corroborated by morphological data, especially regarding lineages 6 and 9,
which despite harboring typical short-snouted species with very similar morphologicalpattern (see Tencatt, Ohara (2016b)) were recovered as completely different clades.
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Luiz F. C. Tencatt, Ondina L. P. Couto, Sérgio A. Santos and Leandro M. Sousa

Except for the lineages 6 and 9, morphological diagnoses for the remaining“Corydoras” lineages are currently available in literature (for lineage 1, see Tencatt etal. (2021); for 4 plus 5, see Bono et al. (2019); for 7, see Tencatt et al. (2023); and for 8,
see Bentley et al. (2021)). Although Corydoras has been recovered as paraphyletic in allcomprehensive phylogenetic hypothesis (e.g., Reis, 1998; Britto, 2003; Alexandrou et al.,2011; Marburguer et al., 2018), the classification of Corydoradinae remains unchanged
since Britto’s (2003) proposal, which may be partially explained by the difficulty indealing with the fact that morphologically similar groups (lineages 6 and 9) wererecovered as clearly distinct clades by Alexandrou et al. (2011).
Contrary to Alexandrou et al. (2011), the two most recent studies investigating theinterrelations within Corydoradinae, the first one by Marburguer et al. (2018), with anuclear-based phylogenetic hypothesis (pyRAD), and then by Dias (2022), with basis
on Ultraconserved Elements, mostly corroborate the morphological data, showing thatlineages 6 and 9 form a monophyletic group, the Hoplisoma Swainson, 1838 clade.
Considering this, a broad study including both morphological and molecular data is
being carried out by A. C. Dias and collaborators (working in progress), which will
establish the monophyly of Corydoras and propose a new classification for the group.
As previously mentioned, the simultaneous presence of some morphological features
undoubtedly places C. caramater as a member of the Corydoras clade (= lineage 1 sensu
Alexandrou et al. (2011)). Therefore, even with the publication of Dias and collaborators
work, the new species will remain allocated in Corydoras.
ACKNOWLEDGMENTS
The Universidade Estadual de Mato Grosso do Sul, the Universidade Federal de Mato
Grosso (UFMT), the Universidade Federal de Mato Grosso do Sul (UFMS) and the
Universidade Federal do Pará (UFPA) provided logistical support. The authors are
grateful to Anja Palandacic (NHM), Carlos Lucena and Margarete Lucena (MCP),
Cláudio Oliveira (LBP), Clemency Fisher and Tony Parker (LIV), Edda Assel and Peter
Bartsch (ZMB), Esther Dondorp (ZMA/RMNH), Mário de Pinna, Aléssio Datovo,
and Osvaldo Oyakawa (MZUSP), Kris Murphy, Sandra Raredon, and Jeffrey Clayton(USNM), Mark Sabaj and Mariangeles Arce (ANSP), Alexandre Ribeiro (CPUFMT),James Maclaine and Oliver Crimmen (BMNH), and Otávio Froehlich (in memoriam)(ZUFMS), Olivier Pauwels and Terry Walschaerts (IRSNB), Patrice Pruvost, Zouhaira
Gabsi, and Jonathan Pfliger (MNHN), Ralph Britz and Mario Richter (MTD F),
and Raphael Covain (MHNG), for hosting museum visits and loaning of material.
To Francisco Severo-Neto and Thomaz Sinani (ZUFMS-PIS), Carlos Lucena and
Héctor Vera-Alcaraz (MCP), Cláudio Oliveira, Ricardo Britzke, Fábio Roxo, Bruno
Melo, and Gabriel Silva (LBP), Claudio Zawadzki and Iago Penido (NUP), Olivier
Pauwels (IRSNB), Willian Ohara, Vinícius Espíndola, Vinícius Reis, and Túlio Teixeira(MZUSP) for generously welcoming LFCT and/or SAS during museum visits. To
Marcos Pinheiro and William Ohara for the invaluable support during the fieldworkin the rio Tapajós basin, Jacareacanga, Pará. To Hans Evers and William Ohara forsending and allowing the use of photos in life of Corydoras caramater. To Fernando Vazde-Mello plus Jorge Arias and Andressa Bach from the Laboratório de Scarabaeoidologia

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A new Corydoras from the Xingu and Tapajós basins(UFMT) for allowing the use and general support of the photomontage equipment
Leica M205C (subproject EECBio UFMT/Finep #01.12.0359.00), respectively. Partof the material available was collected on the federal environmental licensing process
associated with the Belo Monte hydroelectric complex (#02001.001848/2006–75)
and was part of OLPC Master’s Dissertation from Programa de Pós-Graduação em
Biodiversidade e Conservação (PPGBC/UFPA). This study was financed in part by theFundação Universidade Federal de Mato Grosso do Sul, UFMS/MEC, Brazil. We arethankful to Steven Grant for kindly reviewing the English language of this manuscript.
A special thanks to the members of the fish keeping groups Corydoras World (United
Kingdom/UK), Catfish Study Group (UK), Internationale Gemeinschaft Barben Salmler
Schmerlen Welse e.V. (Germany), Potomac Valley Aquarium Society (United Statesof America/USA), Ohio Cichlid Association (USA), All Oddball Aquatics (USA) andGreater Pittsburgh Aquarium Society, Inc. (USA) for the invaluable support to LFCT.

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A new Corydoras from the Xingu and Tapajós basins

AUTHORS’ CONTRIBUTIONLuiz Fernando Caserta Tencatt: Conceptualization, Data curation, Formal analysis, Funding acquisition,
Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization,
Writing-original draft, Writing-review and editing.
Ondina Lillan Pinto do Couto: Data curation, Formal analysis, Investigation, Methodology,
Visualization, Writing-original draft, Writing-review and editing.
Sérgio Alexandre dos Santos: Data curation, Formal analysis, Investigation, Methodology, Visualization,
Writing-original draft, Writing-review and editing.
Leandro Melo de Sousa: Conceptualization, Data curation, Formal analysis, Funding acquisition,
Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization,
Writing-original draft, Writing-review and editing.
ETHICAL STATEMENT
This study was mostly based on museum specimens, and no collecting permit was necessary regarding new
species’ type series; the non-type specimens were collected under the license #85671-1, granted to LFCT by
the Sistema de Autorização e Informação em Biodiversidade (SISBIO).
This is an open access article under the terms of theCreative Commons Attribution License, which permitsuse, distribution and reproduction in any medium,provided the original work is properly cited.

COMPETING INTERESTS
The author declares no competing interests.

Distributed under
Creative Commons CC-BY 4.0© 2024 The Authors.
Diversity and Distributions Published by SBI

HOW TO CITE THIS ARTICLE•

Tencatt LFC, Couto OLP, Santos SA, Sousa LM. A new long-snouted Corydoras(Siluriformes: Callichthyidae) from the rio Xingu and rio Tapajós basins, Brazilian Amazon.
Neotrop Ichthyol. 2024; 22(1):e230112. https://doi.org/10.1590/1982-0224-2023-0112

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Neotropical Ichthyology, 22(1):e230112, 2024

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