Corydoras hypnos, 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 : 15-24

Corydoras hypnos , new species urn:lsid:zoobank.org:act:841242F8-3AE8-4166-A0EA-D76D63340BCE

( Figs. 7-9 ; Tab. 2)

Holotype. MNRJ 53288 , 31.7 mm SL, Brazil, Pará State , Novo Progresso Municipality , rio Jamanxim, a tributary to the rio Tapajós, 08°23’00”S 55°19’08”W, 8 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 384 , 2 , 20.9–26.3 mm SL, stream with unknown name, 08°23’06”S 55°19’43”W, 7 Jul 2019. INPA 59775 , 3 , 22.2–27.2 mm SL, same locality as holotype, 7 Jul 2019. INPA 59774 , 2 , 22.6–28.2 mm SL, same locality as holotype, 11 Jul 2019. CITL 385 , 11 of 13, 17.6–25.7 mm SL, 2 cs of 13, 26.6–32.0 mm SL; MZUSP 126861 , 12 , 13.2–24.7 mm SL; NUP 23541, 11, 18.9–26.1 mm SL, collected with the holotype .

Diagnosis. Corydoras hypnos can be distinguished from its congeners, except for the species from the lineages 6, 7 and 9 sensu Alexandrou et al. (2011) plus C. difluviatilis , C. hastatus , and C. pygmaeus , by having posterior margin of pectoral-fin spine with most serrations directed towards the tip of the spine (vs. most serrations directed towards origin of spine); from C. difluviatilis and C. pygmaeus it differs by the presence of contact between nuchal plate and posterior process of the parieto-supraoccipital (vs. absence of contact between nuchal plate and the posterior process of the parieto-supraoccipital); from C. hastatus by the absence of a large-sized dark blotch on caudal-fin base (vs. caudal-fin base region with a dark brown or black large blotch, roughly diamond-shaped or rhomboid, or arrow-shaped, typically bordered anteriorly and posteriorly by conspicuously light areas); it can be distinguished from the species within lineage 7 by having dark brown or black markings on fins, except for the pectoral and pelvic fins (vs. fins devoid of conspicuous dark markings); it differs from the species within lineages 6 and 9, except for C. benattii , C. eversi Tencatt & Britto, 2016 , C. froehlichi Tencatt, Britto & Pavanelli, 2016 , C. granti Tencatt , Lima & Britto, 2019, C. gryphus Tencatt, Britto & Pavanelli, 2014 , C. psamathos , and C. thanatos , by having dorsal surface of snout with numerous platelets bearing odontodes (vs. dorsal surface of snout lacking platelets); from C. benattii and C. froehlichi by having moderately- to relatively well-developed and smoothly rounded snout (vs. conspicuously short and rounded snout); from C. eversi and C. granti , it can be distinguished by having ventral surface of trunk only with small-sized, non-coalescent platelets (vs. ventral surface of trunk entirely or partially covered by moderate- to relatively large-sized, coalescent platelets); from C. gryphus by having midline of flank with longitudinal series of dark brown or black blotches, when present, diffuse (vs. midline of flank with a longitudinal series of four to six conspicuous dark brown or black blotches), and mesethmoid partially exposed (vs. entirely covered by thick layer of skin); from C. psamathos by the presence of conspicuous dark brown or black markings at least in dorsal and caudal fins (vs. absence of conspicuous dark brown or black markings on body; dark markings, when present, diffuse); from C. thanatos by having anterior laminar expansion moderately developed, poorly expanded towards the anteroventral portion of snout, leaving most of its lateral surface exposed (vs. anterior laminar expansion of infraorbital 1 strongly well developed, conspicuously expanded towards the anteroventral portion of snout, significantly covering its lateral surface).

Description. Morphometric data in Tab. 2. Head laterally compressed with convex dorsal profile, roughly triangular in dorsal view. Snout ranging from moderately to relatively well developed and smoothly rounded. Head profile convex from tip of snout to anterior nares; ascending nearly straight or slightly convex from this point to dorsal-fin origin; region of frontal or parieto-supraoccipital slightly concave in some specimens. Profile slightly convex along dorsal-fin base. Postdorsal-fin body profile slightly concave to adipose-fin spine, slightly concave from this point to caudal-fin base. Ventral profile of body nearly straight or slightly convex from isthmus to pectoral girdle, and slightly convex from this point until pelvic girdle. Profile nearly straight or slightly convex from pelvic girdle to base of first anal-fin ray, ascending slightly concave until caudal-fin base. Body roughly elliptical in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin.

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

Mesethmoid moderate in size, with anterior tip poorly developed, slightly smaller than 50% of bone length (see Britto, 2003:123, character 1, state 1; fig. 1B); posterior portion wide, partially exposed and bearing small odontodes. Nasal capsule delimited posteriorly and dorsally by frontal, anteriorly by mesethmoid, and ventrally and posteriorly by lateral ethmoid. Nasal slender, laterally curved, inner margin with poorly- to moderately-developed laminar expansion generally contacting frontal and mesethmoid; variably close but not in direct contact with mesethmoid; outer margin with poorly-developed to strongly reduced laminar expansion. Lateral ethmoid slightly expanded anteriorly, with anterodorsal expansion relatively distant from nasal, and anterior margin contacting posterior portion of mesethmoid. Frontal elongated, narrow, width less than half of entire length; anterior projection short, size smaller than nasal length. Frontal fontanel large, slender, and somewhat ellipsoid; posterior tip extension slightly surpassing anterior margin of parieto-supraoccipital. Sphenotic somewhat trapezoid, contacting parieto-supraoccipital dorsally, pterotic-extrascapular posteriorly, second infraorbital posteroventrally and frontal anteriorly ( Fig. 8A ). Pterotic-extrascapular roughly pipe-shaped, with posteriormost portion contacting first lateral-line ossicle, posteroventral margin contacting cleithrum, and anteroventral margin contacting opercle; posterior expansion almost entirely covering lateral opening of swimbladder capsule, leaving slender area on its dorsal margin covered only by thick layer of skin. Parieto-supraoccipital wide, posterior process long and contacting nuchal plate; region of contact between posterior process and nuchal plate covered by thick layer of skin.

Two laminar infraorbitals with minute odontodes. Infraorbital 1 large, ventral laminar expansion ranging from poorly to moderately developed; anterior portion with laminar expansion moderately developed, reaching to middle portion of nasal capsule; inner laminar expansion poorly developed ( Fig. 8A ). Infraorbital 2 small, slender, with posterior laminar expansion ranging from strongly reduced to poorly developed; posteroventral margin contacting posterodorsal ridge of hyomandibula, posterodorsal edge contacting only sphenotic; inner laminar expansion ranging from strongly reduced to poorly developed ( Fig. 8A ). Posterodorsal ridge of hyomandibula close to its articulation with opercle relatively slender, exposed, and bearing small odontodes. Dorsal ridge of hyomandibula between pterotic-extrascapular and opercle typically covered by thin skin layer. Interopercle entirely covered by thick layer of skin or almost entirely covered by thick layer of skin, with posterior portion exposed, and typically bearing small odontodes; subtriangular, anterior projection moderately developed. Preopercle elongated, relatively slender; minute odontodes on external surface. Opercle dorsoventrally elongated, with width slightly smaller or similar to half of its entire length; free margin slightly convex, without serrations and covered by small odontodes.

Four branchiostegal rays decreasing in size posteriorly. Hypobranchial 1 deep; hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion well developed, its size about twice or triple of cartilaginous portion. Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with small process on anterior margin of mesial portion; ceratobranchial 3 notched on postero-lateral margin; variably with continuous laminar expansion on postero-lateral margin; ceratobranchial 5 toothed on posterodorsal surface, with 34 to 37(3) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, with small pointed process on laminar expansion of posterior margin; epibranchial 3 with mesially-curved uncinate process on laminar expansion of posterior margin. Two wide pharyngobranchials (3 and 4); pharyngobranchial 3 with smoothly rounded to nearly straight laminar expansion on posterior margin. Upper tooth plate roughly oval, 40 to 53(3) teeth aligned in two rows on posteroventral surface; rows closely aligned.

Lateral-line canal reaching cephalic laterosensory system through 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 with three openings, first on posterior edge, second on posterolateral portion, generally fused with first pore, and third on anterior edge. Infraorbital canal running through entire infraorbital 2, extending to infraorbital 1 and opening into two or three pores. Preoperculomandibular branch giving rise to preoperculo-mandibular canal, which runs through entire preopercle with three openings, leading to pores 3, 4, and 5, respectively; pore 3 variably opening at posterodorsal ridge of hyomandibula.

Dorsal fin subtriangular, located just posterior to second or third dorsolateral body plate. Dorsal-fin rays II,8*(19), II,9(1), posterior margin of dorsal-fin spine with 16 to 17 strongly reduced to poorly-developed serrations; most serrations directed towards tip of spine; some serrations variably perpendicularly directed; serrations absent close to origin of spine; small odontodes on anterior and lateral surfaces of spine ( Fig. 8B ). Nuchal plate moderately developed, almost entirely exposed, with minute odontodes. Spinelet short; spine moderately developed, with adpressed distal tip slightly surpassing posterior origin of dorsal-fin base. Pectoral fin roughly triangular, its origin just posterior to gill opening. Pectoral-fin rays I,7(3), I,7,i(1) or I,8*(16), posterior margin of pectoral spine with 20 to 32 strongly reduced to moderately-developed serrations along its entire length; most serrations directed towards tip of spine; some serrations perpendicularly directed or directed towards origin of spine; serrations variably bifid; small odontodes on anterior, dorsal and ventral surfaces of spine ( Fig. 8C ). Anteroventral portion of cleithrum exposed; posterolateral portion of scapulocoracoid moderately developed, exposed, with anterior portion slightly expanded anteriorly, not in contact with anteroventral portion of cleithrum; exposed areas bearing small odontodes. Opening of axillary gland sensu Kiehl et al. (2006) located just posterior to pectoral-fin spine base. Pelvic fin oblong, located just below first or second ventrolateral body plate, and at vertical through first branched dorsal-fin ray. Pelvic-fin rays i,5*(20). Adipose fin roughly triangular, separated from base of last dorsal-fin ray by generally six dorsolateral body plates. Anal fin subtriangular, typically located just posterior to 12 th ventrolateral body plates, and at vertical through adipose-fin spine base or region of preadipose platelets. Anal-fin rays ii,5(19) or ii,6(1). Caudal fin bilobed, with dorsal and ventral lobes similar in size or dorsal lobe slightly larger than ventral lobe. Caudal-fin rays i,12,i*(20), generally four or five dorsal and ventral procurrent rays.

Typically, three laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, both bearing small odontodes; third, encased in third dorsolateral body plates. Body plates with minute odontodes scattered over exposed area, with conspicuous line of odontodes confined to posterior margins. Dorsolateral body plates 23(17) or 24*(3). Ventrolateral body plates 20(13) or 21*(7). Dorsolateral body plates along dorsal-fin base 6*(18) or 7(2). Dorsolateral body plates between adipose- and caudal-fin 7(18) or 8*(2). Preadipose platelets 3*(6) or 4(14). Ventral surface of trunk between posteroventral margin of cleithrum and pelvic-fin origin laterally delimited only by first ventrolateral body plate; ventral portion of first ventrolateral body plate slightly expanded anteriorly. Small platelets covering base of caudal-fin rays. Small platelets disposed dorsally and ventrally between junctions of lateral plates on posterior portion of caudal peduncle. Anterior margin of orbit, above region of junction between frontal and lateral ethmoid, ventral margin of nasal capsule, above lateral ethmoid, and dorsal surface of snout with numerous small- to relatively large-sized platelets bearing odontodes; platelets on anterior margin of orbit and ventral margin of nasal capsule typically larger and coalescent. Ventral surface of trunk with scarce to relatively numerous small-sized irregular platelets bearing odontodes; platelets more concentrated anteriorly and/or around pectoral-fin base.

Vertebral count 21(3); ribs 5(3); first pair conspicuously large, its middle portion closely connected to first ventrolateral body plate; its tip connected to anterior external process of basipterygium. Parapophysis of complex vertebra well developed.

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

Color in life. Similar to color pattern of preserved specimens, but with light ground color of body and slightly more evident stripe from anteroventral portion of eye to upper lip lateral area. Body covered by greenish yellow iridescent coloration ( Fig. 9 ). Aquarium specimens were observed to present dorsal and lateral surface of head plus lateral surface of cleithrum with irregular, rounded or vermiculated, conspicuous dark brown or black blotches, and conspicuous blotches on body. Some specimens with ground color of body greyish yellow ( Fig. 10 ).

Sexual dimorphism. Similar to the described for Corydoras thanatos , except by the absence of elongated dorsal fin in males, which was not observed so far in both wild caught or aquarium specimens.

Geographical distribution. Corydoras hypnos is currently known from the rio Jamanxim and one of its tributaries, with unknown name, rio Tapajós basin, Novo Progresso Municipality, Pará State, Brazil ( Fig. 5 ).

Ecological notes. Specimens of Corydoras hypnos were always observed by the authors in syntopy and shoaling together with C. thanatos , information on its natural history and habitat notes can be found in the “Ecological notes” section of C. thanatos .

Etymology. The specific epithet “ hypnos ” refers to Hypnos (from the Greek Ύπνος, Ýpnos, which means “sleep”), the Greek god or personification of sleep, and the twin brother of Thanatos, the god/personification of death. The name makes an allusion to the fact that even though both C. hypnos and C. thanatos may present some similarities (in color pattern), they are completely different in other aspects (general morphological pattern). A noun in apposition.

Conservation status. Corydoras hypnos is currently known from its type locality and an additional record in its surroundings. However , both records are in the border of a conservation unit, the Floresta Nacional do Jamanxim , and no threat to the species as a whole is currently suspected. According to the International Union for Conservation of Nature ( IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019), Corydoras hypnos can be classified as Least Concern (LC).

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 7 | Corydoras hypnos, holotype, MNRJ 53288, 31.7 mm SL, Brazil, Pará State, Novo Progresso Municipality, rio Jamanxim, a tributary to the rio Tapajós basin.

FIGURE 8 | 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 hypnos, CITL 385, 32.0 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 9 | Paratypes of Corydoras hypnos photographed alive, showing general color pattern and morphology in lateral view in (A) INPA 59775, 26.2 mm SL, (B) INPA 59775, 27.2 mm SL, (C) INPA 59775, 22.2 mm SL, (D) INPA 59774, 28.2 mm SL, and (E) INPA 59774, 22.6 mm SL, all from the rio Jamanxim, rio Tapajós basin, Pará State, Brazil.

FIGURE 10 | Uncatalogued aquarium specimens of Corydoras hypnos photographed alive, showing general morphology and color pattern of (A) a specimen with brownish yellow ground color of body, and (B) and two specimens with greyish yellow ground color of body. Photos by Robert McLure (A) and Oliver Lucanus (B).