Corydoras maclurei, Tencatt & Gomes & Evers, 2023

Tencatt, Luiz Fernando Caserta, Gomes, Vandergleison de Carvalho & Evers, Hans-Georg, 2023, A new species of Corydoras (Siluriformes: Callichthyidae) from the rio Madre de Dios basin, Peruvian Amazon, with comments on Corydoras aeneus identity, Neotropical Ichthyology (e 230023) 21 (2), pp. 1-28 : 4-19

Corydoras maclurei , new species

urn:lsid:zoobank.org:act:6B46E526-B3D6-4AE5-BC45-D28937C9CFC2

( Figs. 1–9 ; Tab. 1 )

Holotype. MUSM 70671 , 37.0 mm SL, Peru, Cusco Region, Quispicanchi Province, Camanti District, small stream tributary to the rio Araza , a bigger affluent of the rio Inambari , itself a tributary to the rio Madre de Dios, rio Madeira basin, 13°16’18”S 70°46’33”W, 23 Sep 2016, H.-G. Evers, L. Peck & J. Christian.

Paratypes. CITL 430 , 10 of 13, 21.7–41.1 mm SL, 3 c&s of 13, 38.2–47.8 mm SL; CPUFMT 7890, 3, 36.7–38.1 mm SL; MNRJ 53756, 4 , 33.8–35.1 mm SL; MZUSP 127620, 3 , 35.0– 40.9 mm SL; NUP 24254, 3, 34.6–40.3 mm SL, all collected with the holotype .

Diagnosis. Corydoras maclurei can be distinguished from its congeners, except for C. difluviatilis Britto & Castro, 2002 , C. flaveolus Ihering, 1911 , C. gladysae , C. gracilis Nijssen & Isbrücker, 1976 , C. hastatus Eigenmann & Eigenmann, 1888 , C. hephaestus Ohara, Tencatt & Britto, 2016 , C. latus , C. melanotaenia Regan, 1912 , C. micracanthus Regan, 1912 , C. nanus , C. petracinii , C pygmaeus Knaack, 1966 , and C. undulatus Regan, 1912 , by the absence of contact between the posterior process of the parieto-supraoccipital and the nuchal plate (vs. bones in contact). The new species can be distinguished from C. difluviatilis , C. flaveolus , C. gladysae , C. gracilis , C. hastatus , C. hephaestus , C. latus , C. melanotaenia , C. micracanthus , C. nanus , C. petracinii , C pygmaeus , and C. undulatus by having just a single, large conspicuous dark brown or black blotch on anterodorsal portion of flank; blotch somewhat rounded to roughly diamond shaped (vs. flank covered by numerous dark markings, variably with a distinct longitudinal series of blotches along flank midline in C. difluviatilis ; covered by numerous dark markings, with a distinct longitudinal series of blotches along flank midline in C. flaveolus , C. gladysae , C. micracanthus , and C. petracinii ; dorsal portion of flank with a long, arched, continuous dark stripe, which runs parallel to body dorsal profile, extending at least from corner of mouth region to posterior portion of caudal peduncle, dorsally and ventrally bordered by scarcely spotted regions, which often form longitudinal brownish yellow longitudinal bands; ventrolateral body plates with small dark brown or black blotches, variably aligned in longitudinal rows in C. gracilis ; midline of flank with a slender dark longitudinal stripe, which may be absent or diffuse in some individuals; ventral margin of flank, just posterior to pelvic fin, with a small spot or dark longitudinal stripe, which generally becomes gradually diffuse posteriorly; stripe/spot variably diffuse; posterior portion of caudal peduncle with large, conspicuous dark blotch; midline longitudinal stripe, when present, variably fused to peduncular blotch in C. hastatus ; a single, extremely large dark patch, typically almost entirely covering flank in C. hephaestus ; ventral portion of dorsolateral body plates and dorsal portion of ventrolateral body plates with a longitudinal row of brownish yellow small roundish areas, more evident on flank anterior half; remaining areas of dorsolateral body plates with conspicuous concentration of dark brown or black chromatophores, more evident on flank anterior half; dorsal half of ventrolateral body plates, except for small brownish yellow roundish areas, with conspicuous concentration of dark brown or black chromatophores in C. latus ; wide, longitudinal dark stripe almost entirely covering dorsal and middle portion of flank in C. melanotaenia ; dorsal portion of flank with a long, continuous, regular, longitudinal dark brown or black stripe, which runs in parallel to body dorsal profile, extending at least from dorsal-fin base anterior portion to caudal peduncle posterior portion; dorsally and ventrally bordered by scarcely spotted regions, which often form longitudinal brownish yellow longitudinal bands; ventral portion of dorsolateral body plates and dorsal portion of ventrolateral body plates with a series of longitudinally aligned dark brown or black spots, which merge at dorsal-fin region and form a stripe, that can range from narrow to broad; ventrolateral body plates with dark brown or black blotches, generally longitudinally aligned in C. nanus ; dorsal half of dorsolateral body plates densely covered by dark brown or black chromatophores; midline of flank with a longitudinal dark stripe, extending from corner of mouth region to posterior portion of caudal peduncle, dorsally and ventrally bordered by pale regions; ventral margin of flank, just posterior to pelvic fin, with a dark longitudinal stripe; posterior portion of caudal peduncle with moderate-sized, horizontally ellipsoid to roughly diamond shaped conspicuous dark blotch; midline longitudinal stripe fused to peduncular blotch; anterior portion of flank on region between midline and ventral stripes variably with longitudinally aligned dark spots in C. pygmaeus ; with relatively large dark brown or black markings, forming a marbled or somewhat anastomosed pattern at least on anterior portion of flank; blotches variably forming up to three irregular and/or intermittent longitudinal bands; first band, if present, along dorsolateral body plates, second, if present, along midline of flank, and third, if present, along ventrolateral body plates; third band variably more regular and continuous in C. undulatus ). Corydoras maclurei can be additionally distinguished from C. difluviatilis , C. flaveolus , C. gladysae , C. gracilis , C. hastatus , C. micracanthus , C. nanus , C. petracinii , and C. pygmaeus by the absence of dark blotches on fins (vs. at least one of the fins with conspicuous dark blotches).

Description. Morphometric data in Tab. 1 . Head laterally compressed with convex dorsal profile, roughly triangular in dorsal view. Snout typically moderately developed, rounded; variably short and/or smoothly pointed. 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 anterior portion of parieto-supraoccipital and/or region between posterior process of parieto-supraoccipital and nuchal variably slightly concave. Profile slightly convex along dorsal-fin base. Postdorsal-fin body profile slightly concave to nearly straight to adipose-fin spine, 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 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 ( Fig. 2 ). 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 moderate in size, almost reaching or reaching anteroventral limit of gill opening. Outer mental barbel slightly longer than maxillary barbel. Inner mental barbel fleshy, base of each counterpart slightly separated from each other. Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout and isthmus.

Mesethmoid short to 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 relatively wide, laterally curved, inner margin with moderately-developed laminar expansion contacting only frontal; close but not directly in contact with mesethmoid; outer margin with poorly-developed laminar expansion ( Figs. 2A , 3 ). Lateral ethmoid relatively slender in lateral view, slightly expanded anteriorly, with anterodorsal expansion relatively distant from nasal, and anterior margin contacting posterior portion of mesethmoid ( Fig. 2B ). Frontal elongated, narrow, width less than half of entire length; anterior projection short, size smaller than nasal length ( Fig. 3 ). Frontal fontanel large, slender, and somewhat ellipsoid; posterior tip extension slightly surpassing anterior margin of parieto-supraoccipital ( Fig. 3 ). Sphenotic somewhat trapezoid, contacting parieto-supraoccipital dorsally, pterotic-extrascapular posteriorly, second infraorbital posteroventrally and frontal anteriorly ( Fig. 2A ). Pterotic-extrascapular roughly pipe-shaped, with posteriormost portion contacting first lateral-line ossicle, posteroventral margin contacting cleithrum, and anteroventral margin contacting opercle and infraorbital 2; posterior expansion almost entirely covering lateral opening of swimbladder capsule, leaving slender area on its dorsal margin covered only by thick layer of skin. Parieto-supraoccipital wide, posterior process long, not contacting nuchal plate; nearly contacting in some specimens; region between posterior process and nuchal plate covered by thick layer of skin; variably with small- to moderate-sized platelets ( Fig. 4 ).

Two laminar infraorbitals with minute odontodes. Infraorbital 1 large, ventral laminar expansion well developed ( Figs. 2A , 5A ); some specimens with moderately-developed expansion; anterior portion with well-developed laminar expansion, surpassing middle of nasal capsule; inner laminar expansion moderately developed ( Fig. 5B ). Infraorbital 2 small, relatively wide, with posterior laminar expansion strongly well developed ( Figs. 2A , 5A ); posteroventral margin contacting posterodorsal ridge of hyomandibula, posterior margin contacting opercle, and posterodorsal edge contacting sphenotic and pterotic-extrascapular ( Fig. 2A ); posterior margin with roughly triangular process on its middle portion; process smoothly curved downwards ( Fig. 5A ), with tip just above dorsal edge of posterodorsal ridge of hyomandibula ( Fig. 2A ); inner laminar expansion moderately developed ( Fig. 5B ). Posterodorsal ridge of hyomandibula close to its articulation with opercle slender, exposed, and bearing small odontodes ( Figs. 2A , 5C ). Dorsal ridge of hyomandibula between pterotic-extrascapular and opercle typically covered by posterodorsal edge of infraorbital 2; variably covered by thick layer of skin. Interopercle partially covered by thick layer of skin, with posterior portion exposed and bearing odontodes; subtriangular, anterior projection ranging from moderately to well developed ( Figs. 2A , 5C ). Preopercle elongated, relatively slender; minute odontodes on external surface ( Figs. 2A , 5C ). Opercle dorsoventrally elongated; relatively compact in shape, with width larger than half of its entire length; free margin convex, without serrations and covered by small odontodes ( Figs. 2A , 5C ).

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 cartilaginous portion. Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with strongly reduced to small process on anterior margin of mesial portion; ceratobranchial 3 with continuous laminar expansion on postero-lateral margin; laminar expansion variably notched; ceratobranchial 5 toothed on posterodorsal surface, with 32 to 39 (3) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, with small pointed process on laminar expansion of posterior margin; epibranchial 3 with mesially-curved uncinate process on laminar expansion of posterior margin; uncinate process variably roughly triangular. Two wide pharyngobranchials (3 and 4); pharyngobranchial 3 with relatively large triangular laminar expansion on posterior margin; laminar expansion variably notched. Upper tooth plate roughly oval, 41 to 49 (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 and typically fused with first pore, and third on anterior edge. Infraorbital canal running through entire infraorbital 2, extending to infraorbital 1 and typically 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, located just posterior to second or third dorsolateral body plate. Dorsal-fin rays II,5 (1), II,7 (2), II,8* (17), posterior margin of dorsal-fin spine with seven to 14 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. 6A ). Nuchal plate moderately developed, almost entirely exposed, with minute odontodes. Spinelet short; spine ranging from moderately developed, with adpressed distal tip surpassing middle portion of dorsal-fin base, to well 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 I, 5 (1), I,8 (15), I,9* (4), posterior margin of pectoral spine with 20 to 27 poorly- to moderately-developed serrations along almost its entire length, absent close to origin of spine; most serrations directed towards tip of spine; some serrations perpendicularly directed and/or bifid; variably with some trifid and/or fused serrations; small odontodes on anterior, dorsal and ventral surfaces of spine ( Fig. 6B ). 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 second or third ventrolateral body plate, and at vertical through first or second branched dorsal-fin ray. Pelvic-fin rays i, 4,i (2), i,5* (18). Anterior internal process of basipterygium well developed and ranging from slightly to conspicuously laterally expanded, with obliquely placed dorsal lamina, converging mesially towards anterior edge of process; anterior internal process conspicuously narrow in specimen CITL 430, 45.6 mm SL, apparently due to malformation; anterior external process laminar, moderately developed, ranging from not to slightly expanded posteriorly; dorsal ischiac process well developed, with anterior laminar expansion poorly to moderately expanded anteriorly, and posterior laminar expansion conspicuously expanded posteriorly; anterior and posterior laminar expansions of ischiac process roughly triangular; ventral ischiac process clearly smaller than dorsal process, roughly triangular, slightly bent anteriorly ( Figs. 7A, B ). Adipose fin roughly triangular, separated from base of last dorsal-fin ray by eight or nine dorsolateral body plates. Anal fin subtriangular, located just posterior to 12 th or 13 th ventrolateral body plates, and at vertical through region of preadipose platelets. Anal-fin rays ii,4,i (1), ii,5,i (2), ii,6 (16), 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,7,i (1), i,12,i* (18), i,13,i (1), with generally five dorsal and ventral procurrent rays; small cartilage between upper principal and procurrent caudal-fin rays (presumably opisthural cartilage (Monod, 1968; McDowall, 1999 )) ( Fig. 7C ).

Two or three laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, both bearing small odontodes; third, if present, encased in third dorsolateral body plate. Body plates with minute odontodes scattered over exposed area, with conspicuous line of odontodes confined to posterior margins. Dorsolateral body plates 23 (1), 24 (4), 25* (15); first dorsolateral body plate typically not contacting its counterpart dorsally; nearly contacting in some specimens, counterparts externally separated by conspicuously narrow portion of thick skin layer; first and second dorsolateral body plates contacting their counterparts in single specimen ( CITL 430, 34.8 mm SL), apparently due to malformation. Ventrolateral body plates 21 (5), 22* (14), 23 (1). Dorsolateral body plates along dorsal-fin base 5 (2), 6* (18). Dorsolateral body plates between adipose- and caudal-fin 6 (3), 7* (14), 8 (3). Preadipose platelets 4 (4), 5* (11), 6 (4), 7 (1). Ventral surface of trunk between posteroventral margin of cleithrum and pelvic-fin origin laterally delimited only by first ventrolateral body plate or by first and second ventrolateral body plates; 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, region just anterior to nasal bone, and region below infraorbital 1 variably with smallsized, sparse platelets bearing odontodes. Ventral surface of trunk with scarce smallsized irregular platelets bearing odontodes, more concentrated anteriorly; absence of platelets in some specimens.

Vertebral count 23 (3); ribs 6 (1), 7 (1); first pair conspicuously large, its middle portion closely connected to first ventrolateral body plate; its tip not connected to anterior external process of basipterygium; nearly contacting in some specimens. Parapophysis of complex vertebra moderately or well developed.

Color in alcohol. Overall color of body in Fig. 1 . Ground color of body pale- to brownish yellow or beige, with top of head dark brown. Dorsal and lateral surface of head, and lateral surface of cleithrum covered by dark brown or black chromatophores, not forming blotches; posterior margin of cleithrum with conspicuous concentration of dark brown or black chromatophores, forming thin dark line, which is more evident on dorsal half of cleithrum. Border of pores of laterosensory canals typically with conspicuous concentration of dark brown or black chromatophores. Anterodorsal portion of flank, just below anterior portion of dorsal-fin base, with large, conspicuous dark brown or black blotch, ranging from somewhat rounded to roughly diamond shaped. Remaining portions of dorso- and ventrolateral body plates covered by dark brown or black chromatophores, not forming blotches; ventral portion of ventrolateral body plates, especially on region around pelvic-fin origin, devoid of or with sparse chromatophores. Posterior margin of body plates with conspicuous concentration of dark brown or black chromatophores, forming thin dark lines, typically more evident on dorsal portion of dorsolateral body plates, azygous precaudal and preadipose plates, and on dorsolateral body plates below dorsal-fin base. Dorsal and adipose fins entirely covered by numerous brown or black chromatophores, not forming blotches. Pectoral, pelvic, anal and caudal fins with conspicuous concentrations of brown or black chromatophores on rays, not forming blotches; membranes typically devoid of or with sparse chromatophores.

Color in life. Similar to color pattern of preserved specimens, but with ground color of body typically brownish orange ( Fig. 8A ); variably greyish orange or reddish orange ( Figs. 9A, B ). Dorsal fin reddish orange in some specimens ( Fig. 9C ). Body covered by greenish yellow iridescent coloration, with anterior portion of first dorsolateral body plate typically with orange or yellow bright patch. ( Figs. 9D, E ).

Sexual dimorphism. As well-documented in Corydoradinae (see Britto, 2003; Nijssen, Isbrücker, 1980b; Spadella et al., 2017), male specimens of C. maclurei present a genital papilla, which is lanceolate or somewhat tubular in shape.

Geographical distribution. Corydoras maclurei is currently known from tributaries to the rio Araza , an affluent of the rio Inambari, itself a tributary to the rio Madre de Dios , rio Madeira basin, Camanti District, Quispicanchi Province, Cusco Region, Peru ( Fig. 10 ).

Ecological notes. Corydoras maclurei was captured in clearwater creeks and smaller rivers tributaries to the rio Madre de Dios drainage around the town of Quince Mil ( Fig. 8B ). The habitats are mostly very shallow, raising their water levels only after stronger rainfalls, which return to normal levels after a few hours. The water temperatures measured by HGE lay between 22.3 to 24.9°C during the daytime at different times of the year (June, September). During the night, the air temperatures fall significantly and so do the water temperatures. On June 17th, 2015 at 8 pm the water temperature at the type locality was 18.5 °C. The conductivity lies between 53 µS/cm with a pH at 6.0 (June 17, 2015) and 29 µS/cm with a pH of 7.0 (September 22, 2016). In these sites, the crystal-clear water flows over a bed of pebbles, rocks and boulders, with smaller areas of fine sand. Especially in the very small and narrow creeks, there is also a dense leaf litter covering the ground. During the day, single specimens of C. maclurei could be observed resting between the rocks and quickly hiding under the leaves in case of danger. Night collecting efforts could not be performed as the dense vegetation and rough terrain make collecting fish extremely difficult at this time of day. Even after extensive collecting activities, for several hours, only a few specimens of C. maclurei were captured, suggesting that the new species is naturally not very abundant in the aforementioned biotopes, while the syntopic Corydoras weitzmani Nijssen, 1971 can be observed in pairs or small groups foraging along the river edges.

Etymology. Corydoras maclurei is named in honor of Robert “Rob” McLure, dear friend and renowned Corydoradinae breeder. Rob has been the main English-language reviewer of the first author’s publications, in addition to providing valuable information and live photos of several species of Corydoradinae . A genitive noun.

Conservation status. Even with the extensive survey efforts throughout the region, C. maclurei was exclusively found in some of the small streams draining to the rio Araza around Quince Mil, a small Peruvian community. With the currently available data, the Extent of Occurrence of C. maclurei was roughly estimated to be 5 km 2. All habitats in the vicinity of Quince Mil are vulnerable due to human activities, especially illegal goldmining and road building (see Lujan et al., 2013), increasing problems in the whole rio Inambari basin (Hans -G. Evers, 2016, pers. obs.). Additionally, the new species is desirable in the aquarium hobby, making some fishermen from the Cusco area to perform regular collecting efforts in the Quince Mil area, where they even use rotenone to collect both C. maclurei and C. weitzmani , mostly at night (Hans -G. Evers, 2022, pers. obs.). Considering that the new species seems to occur in low abundance, it is possible that its populations are being overfished, which is aggravated by its restricted geographic distribution and the collecting method applied by the local fishermen (i.e., rotenone). Therefore, according to the International Union for Conservation of Nature ( IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2022), Corydoras maclurei can be classified as Near Threatened (NT), approximating the Critically Endangered (CR) category by criterion B1b(iii).

Remarks. Corydoras maclurei has been bred under aquarium conditions by one of the authors ( HGE), who documented its ontogenetic development from 8 to 28 mm LT, showing general changes in external morphology and color pattern ( Fig. 11 ). Specimen with 8.0 mm TL in yolk-sac stage ( Fig. 11A ); head slightly depressed, with short and conspicuously rounded snout; barbels moderate in size and with well-developed papillae, which will gradually become less developed along individual’s growth; eye large; median fin fold present, extending from postcephalic region to genital opening; fin rays indistinct, with pectoral fin fold oblong; body plates absent; body covered by dark-brown or black chromatophores; body covered by greenish yellow iridescent coloration.

Specimen with 12.0 mm TL in final flexion stage ( Fig. 11B ); dorsal- and caudal-fin rays distinct, but fins not detached from fin fold; pectoral-fin rays distinct; anal, pelvic and adipose fins not distinct; caudal-fin asymmetrical, dorsal portion distinctly longer than ventral; hypural plates visible by transparency; conspicuous, oblique dark stripe from anteroventral margin of orbit to upper lip lateral area. Specimen with 16.0 mm TL in early post-flexion stage ( Fig. 11C ) displays more pronounced snout; reduction of median fold, with dorsal, anal and caudal fins partially detached; pectoral fin slightly more developed; pelvic- and anal-fin rays distinct; adipose fin indistinct; beginning of formation of lateral body plates; slightly more pigmented body, with diffuse dark patches. Juvenile specimens with 21.0 and 28.0 mm TL ( Figs. 11D, E ), respectively, are strongly similar to each other, except for except for gradual development of lateral body plates and fin spines, and conspicuous dark patch on anterodorsal portion of flank in larger specimen; snout slightly more pronounced; median fold absorbed, with distinct adipose, caudal and anal fins.

Figures

FIGURE 1 | Corydoras maclurei, holotype, MUSM 70671, 37.0 mm SL, Camanti District, Quispicanchi Province, Cusco Region, Peru, small stream tributary to the rio Araza, a bigger affluent of the rio Inambari, itself a tributary to the rio Madre de Dios, rio Madeira basin.

FIGURE 2 | Head osteological pattern in c&s paratypes of Corydoras maclurei, showing (A) general morphology in lateral view (CITL 430, 47.8 mm SL), with (B) the detail of the lateral ethmoid morphology (CITL 430, 38.2 mm SL). Abbreviations: f: frontal, fdbp: first dorsolateral body plate, io1–2: infraorbital 1 and 2, iop: interopercle, le: lateral ethmoid, n: nasal, me: mesethmoid, op: opercle, pes: pteroticextrascapular, pop: preopercle, prh: posterodorsal ridge of hyomandibula, pso: parieto-supraoccipital, sph: sphenotic. Scale bar = 1 mm.

FIGURE 3 | Dorsal view of the head of a c&s paratype of Corydoras maclurei, CITL 430, 47.8 mm SL. Abbreviations: f: frontal, fdbp: first dorsolateral body plate, n: nasal, me: mesethmoid, pes: pteroticextrascapular, pso: parieto-supraoccipital, sph: sphenotic. Scale bar = 1 mm.

FIGURE 4 | Predorsal region of trunk in c&s paratypes of Corydoras maclurei, showing the variation in the distance between the posterior process of the parieto-supraoccipital and the nuchal plate, which ranges from (A) clearly separated from each other (CITL 430, 45.6 mm SL) to (B) separated but nearly contacting (CITL 430, 38.2 mm SL). Abbreviations: fdbp: first dorsolateral body plate, np: nuchal plate, pso: parieto-supraoccipital, spn: spinelet. Dotted lines indicate the limits of the tip of the posterior process of the parieto-supraoccipital and anterior tip of the nuchal plate. Red arrows indicate the small platelets between parieto-supraoccipital and nuchal plate. Scale bar = 1 mm.

FIGURE 5 | Infraorbital series in lateral (A) and dorsal (B) views, and (C) suspensorium plus operculum in lateral view of a c&s paratype of Corydoras maclurei (CITL 430, 38.2 mm SL). Abbreviations: aa: anguloarticular, 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. Black arrow indicates the roughly triangular process on middle portion of posterior margin of infraorbital 2, and red arrows indicate inner laminar expansion of both infraorbitals. Scale bar = 1 mm.

FIGURE 6 | Lateral view of (A) the dorsal-fin spine (38.2 mm SL) and dorsal view of (B) the right pectoral-fin spine (47.8 mm SL), showing the serration patterns in c&s paratypes of Corydoras maclurei (CITL 430). Scale bars = 1 mm.

FIGURE 7 | Pelvic girdle and caudal skeleton in c&s paratypes of Corydoras maclurei (CITL 430). A. Anterior internal process of basipterygium slightly laterally expanded, and anterior external process not expanded posteriorly (38.2 mm SL); B. Anterior internal process of basipterygium conspicuously laterally expanded, and anterior external process slightly expanded posteriorly (47.8 mm SL); C. General morphology of caudal skeleton, showing the small cartilage (yellow arrow) between upper principal and procurrent caudal-fin rays (38.2 mm SL). Abbreviations: bp: basipterygium, 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, pae: anterior external process, pai: anterior internal process, par: parhypural, pi: dorsal ischiac process, pu 2–4: preural centra 2 to 4, un: uroneural. Red arrows in A and B indicate the dorsal lamina on anterior internal process of basipterygium. Scale bars = 1 mm.

FIGURE 8 | Uncatalogued aquarium specimen of Corydoras maclurei (A) showing its typical color pattern in life (lateral view), collected in its type-locality (B), a small stream tributary to the rio Araza, rio Madre de Dios basin, rio Madeira basin in Peru.

FIGURE 9 | Uncatalogued aquarium specimens of Corydoras maclurei (not measured) showing variations of the color pattern in life: specimens can variably present greyish orange (A) or reddish orange (B) ground color of body. In C, the detail of a conspicuously reddish orange dorsal fin. Anterior portion of first dorsolateral body plate typically with orange (D) or yellow (E) bright patch. Photographs (D) and (E) by Ian Fuller.

FIGURE 10 | Map showing the geographical distribution of Corydoras maclurei (yellow star). The symbol represents more than one locality.

FIGURE 11 | Ontogenetic series of Corydoras maclurei (bred under aquarium conditions) showing general changes in external morphology and color pattern in specimens with 8.0 mm TL (A), 12.0 mm TL (B), 16.0 mm TL (C), 21.0 mm TL (D), and 28.0 mm TL (E).

Tables

TABLE 1 | Morphometric data of the holotype and 19 paratypes of Corydoras maclurei. SD = Standard deviation.

	Holotype	Low–High	Mean±SD
Standard length (mm)	37.0	22.8–41.1	36.2 ± 3.9
Percentage of standard length
Depth of body	35.4	30.7–35.4	33.4 ± 1.4
Predorsal distance	52.2	47.3–54.6	51.1 ± 2.0
Prepelvic distance	48.4	43.3–51.4	46.9 ± 2.0
Preanal distance	83.8	77.9–84.7	81.5 ± 1.8
Preadipose distance	90.5	81.8–91.7	88.3 ± 2.2
Length of dorsal spine	14.6	12.3–17.9	15.2 ± 1.6
Length of pectoral spine	24.9	18.0–26.9	22.9 ± 2.5
Length of adipose–fin spine	10.3	7.1–10.4	9.2 ± 1.1
Depth of caudal peduncle	15.4	15.1–17.3	15.9 ± 0.5
Length of dorsal–fin base	18.1	11.5–18.1	16.2 ± 1.4
Dorsal to adipose distance	28.1	25.9–31.9	28.4 ± 1.7
Maximum cleithral width	26.2	24.2–29.3	26.1 ± 1.3
Head length	42.7	32.0–52.6	40.6 ± 3.7
Length of maxillary barbel	15.7	5.7–15.7	11.1 ± 3.0
Percentage of head length
Head depth	72.2	58.3–100.0	77.1 ± 7.6
Least interorbital distance	33.5	26.0–46.4	34.0 ± 3.8
Horizontal orbit diameter	17.1	13.0–20.5	17.8 ± 2.0
Snout length	36.7	28.6–46.4	35.9 ± 3.4
Least internarial distance	16.5	13.0–19.6	16.7 ± 1.7