Corydoras psamathos, Tencatt & Ohara & Sousa & Britto, 2022

Tencatt, Luiz Fernando Caserta, Ohara, Willian Massaharu, Sousa, Leandro Melo de & Britto, Marcelo Ribeiro de, 2022, Science and hobby joining forces for the discovery of three new Corydoras (Siluriformes: Callichthyidae) from the rio Tapajós basin, Brazil, with comments on Corydoras sp. CW 111, Neotropical Ichthyology (e 220070) 20 (3), pp. 1-40 : 24-32

Corydoras psamathos , new species urn:lsid:zoobank.org:act:76871FE9-BC24-4B3D-99DA-0249A1E672C7

( Figs. 11-13 ; Tab. 3)

Holotype. MNRJ 53289 , 29.4 mm SL, Brazil, Pará State , Novo Progresso Municipality , igarapé Santa Júlia , a tributary to the rio Jamanxim, rio Tapajós basin, 06°45’38”S 55°28’44”W, 10 Jul 2019, M. R. Britto, W. M. Ohara and L. F. C. Tencatt.

Paratypes. All from Brazil, Pará State, Novo Progresso Municipality, rio Jamanxim basin, rio Tapajós drainage, collected by M . R. Britto, W. M. Ohara and L. F. C. Tencatt . CITL 386 , 3 , 18.1–21.8 mm SL ; INPA 59772 , 1 , 23.7 mm SL, rio Jamanxim , 07°03’52”S 55°26’28”W, 9 Jul 2019 . CITL 387 , 9 of 12, 19.3–29.6 mm SL, 3 cs of 12, 22.0– 28.6 mm SL ; INPA 59773 , 2 , 29.3–30.2 mm SL ; MZUSP 126862 , 10 , 19.6–27.8 mm SL; NUP 23542, 10, 18.7–26.9 mm SL, collected with holotype .

Diagnosis. Corydoras psamathos can be distinguished from its congeners, except for the species from the lineages 6, 7 and 9 sensu Alexandrou et al. (2011) plus C. difluviatilis , C. hastatus and C. pygmaeus , by having posterior margin of pectoral-fin spine with most serrations directed towards the tip of the spine (vs. most serrations directed towards origin of spine); from C. difluviatilis and C. pygmaeus it differs by the presence of contact between nuchal plate and posterior process of the parieto-supraoccipital (vs. absence of contact between nuchal plate and the posterior process of the parieto-supraoccipital); from C. hastatus by the absence of a large-sized dark blotch on caudal-fin base (vs. caudal-fin base region with a dark brown or black large blotch, roughly diamond-shaped or rhomboid, or arrow-shaped, typically bordered anteriorly and posteriorly by conspicuously light areas); from the species within lineage 7, it differs by having posterodorsal edge of infraorbital 2 only in contact with sphenotic (vs. in contact with sphenotic and pterotic-extrascapular); from the species of lineages 6 and 9, except for C. concolor Weitzman, 1961 , C. esperanzae Castro, 1987 , C. guianensis , C. polystictus Regan, 1912 , and C. sanchesi Nijssen & Isbrücker, 1967 , by the absence of conspicuous dark brown or black markings on body; dark markings, when present, diffuse (vs. presence of conspicuous small- to large- sized dark brown or black markings in at least some region of the body); from C. concolor , C. esperanzae , C. guianensis , C. polystictus , and C. sanchesi by having posterior laminar expansion of infraorbital 2 strongly reduced, nearly imperceptible in some specimens (vs. posterior laminar expansion at least poorly developed, but clearly more developed and perceptible), by the slender body (vs. more robust), and by the narrower frontal bone (vs. wider). The new species can be further distinguished from C. concolor and C. esperanzae by the presence of ventral surface of trunk only with small-sized, irregular platelets (vs. ventral surface of trunk entirely or almost entirely covered by larger coalescent platelets); from C. sanchesi by having anterior portion of dorsal fin with scattered dark brown or black chromatophores, not forming any conspicuous pattern (vs. anterior portion of dorsal fin typically with a conspicuous concentration of dark brown or black chromatophores, forming a dark patch); from C. polystictus by presenting dorsal surface of snout with numerous platelets bearing odontodes (vs. dorsal surface of snout lacking platelets).

Description. Morphometric data in Tab. 3. Head laterally compressed with convex dorsal profile, roughly triangular in dorsal view. Snout ranging from relatively short to moderately developed and generally smoothly rounded; slightly more rounded in some specimens. Head profile convex from tip of snout to anterior nares; ascending nearly straight or slightly convex from this point to dorsal-fin origin; region of frontal fontanel slightly concave in some specimens. Profile slightly convex along dorsal-fin base. Postdorsal-fin body profile slightly concave to adipose-fin spine, slightly concave from this point to caudal-fin base. Ventral profile of body nearly straight or slightly convex from isthmus to pectoral girdle, and slightly convex from this point until pelvic girdle. Profile nearly straight or slightly convex from pelvic girdle to base of first anal-fin ray, ascending slightly concave until caudal-fin base. Body roughly elliptical in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin.

Eye rounded, located dorsolaterally on head. Orbit delimited anteriorly by lateral ethmoid, anterodorsally by frontal, posterodorsally by sphenotic, posteroventrally by infraorbital 2, and anteroventrally by infraorbital 1. Anterior and posterior nares close to each other, only separated by flap of skin. Anterior naris tubular. Posterior naris close to anterodorsal margin of orbit, separated from it by distance similar to naris diameter. Mouth small, subterminal, width similar to bony orbit diameter. Maxillary barbel ranging from short to moderate in size, not reaching to anteroventral limit of gill opening. Outer mental barbel slightly longer than maxillary barbel. Inner mental barbel fleshy, base of each counterpart slightly separated from each other. Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout and isthmus.

Mesethmoid moderate in size, with anterior tip poorly developed, slightly smaller than 50% of bone length (see Britto, 2003:123, character 1, state 1; fig. 1B); posterior portion wide, partially exposed and bearing small odontodes. Nasal capsule delimited posteriorly and dorsally by frontal, anteriorly by mesethmoid, and ventrally and posteriorly by lateral ethmoid. Nasal slender, laterally curved, inner margin with poorly- to moderately-developed laminar expansion generally contacting frontal and mesethmoid; variably close but not in direct contact with mesethmoid; outer margin typically with strongly reduced laminar expansion. Lateral ethmoid slightly expanded anteriorly, with anterodorsal expansion relatively distant from nasal, and anterior margin contacting posterior portion of mesethmoid. Frontal elongated, narrow, width less than half of entire length; anterior projection short, size smaller than nasal length. Frontal fontanel large, slender, and somewhat ellipsoid; posterior tip extension slightly surpassing anterior margin of parieto-supraoccipital. Sphenotic somewhat trapezoid, contacting parieto-supraoccipital dorsally, pterotic-extrascapular posteriorly, second infraorbital posteroventrally and frontal anteriorly ( Fig. 12A ). Pterotic-extrascapular roughly pipe-shaped, with posteriormost portion contacting first lateral-line ossicle, posteroventral margin contacting cleithrum, and anteroventral margin contacting opercle; posterior expansion almost entirely covering lateral opening of swimbladder capsule, leaving slender area on its dorsal margin covered only by thick layer of skin. Parieto-supraoccipital wide, posterior process long and contacting nuchal plate; region of contact between posterior process and nuchal plate covered by thick layer of skin.

Two laminar infraorbitals with minute odontodes. Infraorbital 1 large, ventral laminar expansion ranging from poorly to moderately developed; anterior portion with laminar expansion moderately developed, reaching to middle portion of nasal capsule; inner laminar expansion poorly developed ( Fig. 12A ). Infraorbital 2 small, slender, with posterior laminar expansion strongly reduced, nearly imperceptible in some specimens; posteroventral margin contacting posterodorsal ridge of hyomandibula, posterodorsal edge contacting only sphenotic; inner laminar expansion ranging from strongly reduced to poorly developed ( Fig. 12A ). Posterodorsal ridge of hyomandibula close to its articulation with opercle relatively slender, exposed, and bearing small odontodes. Dorsal ridge of hyomandibula between pterotic-extrascapular and opercle typically covered by thick skin layer. Interopercle entirely covered by thick layer of skin; subtriangular, anterior projection ranging from moderately developed to relatively well developed. Preopercle elongated, relatively slender; minute odontodes on external surface. Opercle dorsoventrally elongated, with width similar to half of its entire length; free margin slightly convex, without serrations and covered by small odontodes.

Four branchiostegal rays decreasing in size posteriorly. Hypobranchial 1 deep; hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion ranging from strongly reduced, with only region of tip ossified, to well developed, its size about twice of cartilaginous portion. Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with small process on anterior margin of mesial portion; ceratobranchial 3 typically notched on postero-lateral margin; ceratobranchial 5 toothed on posterodorsal surface, with 28 to 38(3) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, with small pointed process on laminar expansion of posterior margin; epibranchial 3 with mesially-curved uncinate process on laminar expansion of posterior margin. Two wide pharyngobranchials (3 and 4); pharyngobranchial 3 with slightly triangular to smoothly rounded laminar expansion on posterior margin. Upper tooth plate roughly oval, 34 to 43(3) teeth aligned in two rows on posteroventral surface; rows closely aligned.

Lateral-line canal reaching cephalic laterosensory system through pterotic-extrascapular, branching twice before reaching sphenotic: pterotic branch, with single pore, preoperculomandibular branch conspicuously reduced, with single pore opening at postotic main canal; postotic main canal widens just posterior to pterotic branch. Sensory canal continuing through pterotic-extrascapular, reaching sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, other branch connecting to frontal through supraorbital canal, both with single pore. Supraorbital canal branched, running through nasal bone. Epiphyseal branch conspicuously reduced; pore opening close to supraorbital main canal, directed towards frontal fontanel. Nasal canal typically with three openings, first on posterior edge, second on posterolateral portion, generally fused with first pore, and third on anterior edge. Infraorbital canal running through entire infraorbital 2, extending to infraorbital 1 and generally opening into two pores. Preoperculomandibular branch giving rise to preoperculo-mandibular canal, which runs through entire preopercle with three openings, leading to pores 3, 4, and 5, respectively.

Dorsal fin subtriangular, generally located just posterior to second dorsolateral body plate. Dorsal-fin rays II,7*(1) or II,8(19), posterior margin of dorsal-fin spine with 10 to 16 strongly reduced to poorly-developed serrations; most serrations directed towards tip of spine; some serrations variably perpendicularly directed; serrations absent close to origin of spine; small odontodes on anterior and lateral surfaces of spine ( Fig. 12B ). Nuchal plate moderately developed, almost entirely exposed, with minute odontodes. Spinelet short; spine moderately developed, with adpressed distal tip slightly surpassing posterior origin of dorsal-fin base. Pectoral fin roughly triangular, its origin just posterior to gill opening. Pectoral-fin rays I,7*(5), I,7,I(3) or I,8(12), posterior margin of pectoral spine with 17 to 26 strongly reduced to moderately-developed serrations along its entire length; most serrations directed towards tip of spine; some serrations perpendicularly directed; small odontodes on anterior, dorsal and ventral surfaces of spine ( Fig. 12C ). Anteroventral portion of cleithrum exposed; posterolateral portion of scapulocoracoid moderately developed, exposed, with anterior portion slightly expanded anteriorly, not in contact with anteroventral portion of cleithrum; exposed areas bearing small odontodes. Opening of axillary gland sensu Kiehl et al. (2006) located just posterior to pectoral-fin spine base. Pelvic fin oblong, located just below first or second ventrolateral body plate, and at vertical through first branched dorsal-fin ray. Pelvic-fin rays I,5*(20). Adipose fin roughly triangular, separated from base of last dorsal-fin ray by generally six dorsolateral body plates. Anal fin subtriangular, typically located just posterior to 12 th or 13 th ventrolateral body plates, and at vertical through adipose-fin spine base. Anal-fin rays ii,5(18), ii,5,i*(1), ii,7(1). Caudal fin bilobed, with dorsal and ventral lobes similar in size or dorsal lobe slightly larger than ventral lobe. Caudal-fin rays I,12,i*(20), generally five dorsal and ventral procurrent rays.

Typically, three laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, both bearing small odontodes; third, encased in third dorsolateral body plates. Body plates with minute odontodes scattered over exposed area, with conspicuous line of odontodes confined to posterior margins. Dorsolateral body plates 23(2), 24*(15) or 25(3). Ventrolateral body plates 21(15) or 22*(5). Dorsolateral body plates along dorsal-fin base 6*(17) or 7(3). Dorsolateral body plates between adipose- and caudal-fin 7(2), 8*(17) or 9(1). Preadipose platelets 3*(14) or 4(6). Ventral surface of trunk between posteroventral margin of cleithrum and pelvic-fin origin laterally delimited only by first ventrolateral body plate; ventral portion of first ventrolateral body plate slightly expanded anteriorly. Small platelets covering base of caudal-fin rays. Small platelets disposed dorsally and ventrally between junctions of lateral plates on posterior portion of caudal peduncle. Anterior margin of orbit, above region of junction between frontal and lateral ethmoid, ventral margin of nasal capsule, above lateral ethmoid, and dorsal surface of snout with numerous small- to relatively large-sized platelets bearing odontodes; platelets on anterior margin of orbit and ventral margin of nasal capsule typically larger and coalescent. Ventral surface of trunk with scarce small-sized irregular platelets bearing odontodes; platelets more concentrated anteriorly and/or around pectoral-fin base.

Vertebral count 22(3); ribs 5(3); first pair conspicuously large, its middle portion closely connected to first ventrolateral body plate; its tip connected to anterior external process of basipterygium. Parapophysis of complex vertebra well developed.

Color in alcohol. Overall color of body in Fig. 11 . Ground color of body paleto brownish yellow or beige. Top of head dark brown; dark area typically extending mesially towards posterior tip of parieto-supraoccipital as thin longitudinal line. Dorsal and lateral surface of head and lateral surface of cleithrum with conspicuous concentrations of dark brown or black chromatophores, typically not forming blotches; top of head with diffuse irregular dark blotches in some specimens; diffuse stripe from anteroventral portion of eye to upper lip lateral area typically present. Dorsolateral body plates with conspicuous concentration of dark brown or black chromatophores, typically not forming dark blotches; diffuse rounded, irregular or vertically elongated dark blotches in some specimens; dorsal portion of plates with slightly more concentrated chromatophores on anterior and posterior origins of dorsal fin, adipose-fin base, and caudal-fin base in some specimens. Ventrolateral body plates, except for ventral portion of plates between pelvic-fin origin to area just anterior to anal-fin origin, with conspicuous concentration of dark brown or black chromatophores, typically not forming dark blotches; diffuse rounded, irregular or vertically elongated dark blotches in some specimens; ventral portion of plates between pelvic-fin origin to area just anterior to anal-fin origin, especially around pelvic-fin origin, typically with sparse dark brown or black chromatophores, not forming any distinctive pattern. Midline of flank with distinct longitudinal series of diffuse dark brown or black blotches, more evident on posterior half of flank in single juvenile specimen (18.4 mm SL). Blotches on flanks typically small. Posterior margin of body plates typically with dark brown or black chromatophores, variably forming thin dark lines along border of plates. Dorsal-fin with dark brown or black chromatophores, especially on rays, generally not forming evident blotches; forming strongly faded to diffuse small dark blotches in some specimens; chromatophores typically more numerous and concentrated on dorsal half of first branched-ray region, including membranes, and along dorsal-fin proximal portion. Pectoral, pelvic, and anal fins with sparse to relatively numerous dark brown or black chromatophores, especially on rays, typically not forming dark spots; chromatophores on anal fin more concentrated on its proximal half. Adipose fin with conspicuous concentrations of dark brown or black chromatophores on spine; dark brown or black chromatophores on membrane typically more numerous and concentrated on its posterior margin and/or along its proximal portion, not forming any conspicuous pattern. Caudal fin with dark brown or black chromatophores, mainly on rays, typically forming closely-spaced, strongly faded to diffuse dark blotches; some specimens with blotches roughly aligned transversally in up to nine slender and closely-spaced rows of blotches; some specimens with non-aligned blotches; dark blotches variably absent.

Color in life. Similar to color pattern of preserved specimens, but with light ground color of body and slightly more evident stripe from anteroventral portion of eye to upper lip lateral area. Body covered by greenish yellow iridescent coloration ( Fig. 13 ). Some aquarium specimens with greyish-white ground color of body ( Fig. 14 ).

Sexual dimorphism. Same as described for Corydoras hypnos .

Geographical distribution. Corydoras psamathos is currently known from the main channel of the rio Jamanxim and one of its tributaries, the igarapé Santa Júlia, rio Tapajós basin Novo Progresso Municipality, Pará State, Brazil ( Fig. 5 ).

Ecological notes. The new species was observed to inhabit the rio Jamanxim and at least one of its tributaries, the igarapé Santa Júlia. In the rio Jamanxim, it was mostly associated with the margins of the river, where juvenile and adult specimens were observed in the shallow (up to about 20 cm deep) sandy shores with slow water flow. In the igarapé Santa Júlia ( Fig. 15 ), juvenile and adult specimens were also observed associated in marginal shallow (up to about 20 cm deep) portions, with more complex substrate, mainly composed by sand, fine gravel and larger rocks. In this site, both juvenile and adult specimens of C. psamathos were observed shoaling together with juvenile specimens of Corydoras sp. CW171, being the new species clearly more abundant. Additionally, C. apiaka was observed syntopically with the new species and Corydoras sp. CW 171 in the igarapé Santa Júlia. In both sampled sites, the new species was mostly captured at night.

Etymology. The specific epithet “ psamathos ” refers to Psamathos Psamathides, the oldest wizard among the Psamathists, the sand sorcerers, a fictional character created by J. R. R. Tolkien in his book Roverandom. The name derives from the Greek psammos, which means sand. The name alludes to the sand-dwelling behavior of the new species. A noun in apposition.

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

Figures

FIGURE 5 | Map of the rio Tapajós and adjoining areas, showing the geographical distribution of Corydoras thanatos (black circle), C. hypnos (white star), and C. psamathos (red squares). Each symbol may represent more than one locality.

FIGURE 11 | Corydoras psamathos, holotype, MNRJ 53289, 29.4 mm SL, Novo Progresso Municipality, Pará State, Brazil, igarapé Santa Júlia, a tributary to the rio Jamanxim, rio Tapajós basin.

FIGURE 12 | Lateral view of the head (A), lateral view of the dorsal-fin spine (B) and dorsal view of the left pectoral-fin spine (C) in cs paratype of Corydoras psamathos, CITL 387, 28.6 mm SL. Abbreviations: f: frontal, io1–2: infraorbital 1 and 2, iop: interopercle, n: nasal, op: opercle, pes: pterotic-extrascapular, pop: preopercle, prh: posterodorsal ridge of hyomandibula, pso: parieto-supraoccipital, sph: sphenotic. Scale bars = 1 mm.

FIGURE 13 | Paratypes of Corydoras psamathos photographed alive, showing general color pattern and morphology in lateral view in (A) INPA 59772, 23.7 mm SL, (B) INPA 59773, 30.2 mm SL, and (C) INPA 59773, 29.3 mm SL. Specimen (A) is from the rio Jamanxim, and specimens (B–C) are from the igarapé Santa Júlia, rio Tapajós basin.

FIGURE 14 | Uncatalogued aquarium specimen of Corydoras psamathos photographed alive. Photo by Takayuki Shimizu.

FIGURE 15 | Type locality of Corydoras psamathos, the igarapé Santa Júlia, a tributary to the rio Jamanxim, rio Tapajós basin in Pará State, Brazil.