Aspidoras albater Nijssen & Isbrücker, 1976

Tencatt, Luiz Fernando Caserta, Britto, Marcelo R., Isbrücker, Isaäc Jan Hendrik & Pavanelli, Carla Simone, 2022, Taxonomy of the armored catfish genus Aspidoras (Siluriformes: Callichthyidae) revisited, with the description of a new species, Neotropical Ichthyology (e 220040) 20 (3), pp. 1-159 : 23-38

Aspidoras albater Nijssen & Isbrücker, 1976

( Fig. 11 )

Aspidoras albater Nijssen & Isbrücker, 1976:115 (original description; type locality: rio Tocantinzinha [sic, = Tocantinzinho] near São João da Aliança, Goiás State, Brazil). — Britto, 1998:360 (listed as comparative material; partim). — Britto, 2000:1054 (listed as comparative material; partim). — Lima, Britto, 2001:1015 (listed as comparative material; partim). —Reis, 2003:292 (listed). —Ferraris, 2007:108 (listed). —Wosiacki et al., 2014:311 (morphological comparison, listed as comparative material). —Tencatt, Bichuette, 2017:8 (morphological comparison).

Aspidoras eurycephalus Nijssen & Isbrücker, 1976:118 (original description; type locality: Vermelho Stream into rio das Almas, Goiás State, Brazil; new synonym). —Reis, 2003:292 (listed). —Ferraris, 2007:109 (listed). —Tencatt, Bichuette, 2017:8 (morphological comparison).

Aspidoras poecilus (non Nijssen, Isbrücker, 1976): —Oliveira et al., 2017:e160118[7] (listed as comparative material; partim).

Aspidoras aff. poecilus (non Nijssen, Isbrücker, 1976): — Britto, 1998:361 (listed as comparative material; partim). — Britto, 2000:1054 (listed as comparative material; partim). — Lima, Britto, 2001:1015 (listed as comparative material; partim).

Aspidoras taurus Lima & Britto, 2001:1011 (original description; type locality: rio Itiquira , Mato Grosso State, Brazil; partim; new synonym). — Ferraris , 2007:110 (listed). — Wosiacki et al., 2014:311 (morphological comparison, listed as comparative material). — Tencatt, Bichuette, 2017:21 (listed as comparative material) .

Diagnosis. Aspidoras albater can be distinguished from its congeners, with exception of A. aldebaran , A. azaghal , A. depinnai , A. fuscoguttatus , A. gabrieli , A. lakoi , and A. poecilus , by having inner laminar expansion of infraorbital 1 ranging from well developed to extremely well developed (vs. moderately developed in A. belenos , A. maculosus , A. mephisto , and A. raimundi ; poorly developed in A. psammatides and A. velites ); it differs from A. fuscoguttatus by having anterior portion of infraorbital 1 with laminar expansion ranging from strongly reduced, at same level as posterior margin of nasal capsule, to moderately-developed expansion, reaching middle of nasal capsule (vs. expansion ranging from well developed, surpassing middle of nasal capsule, to extremely well developed, reaching anterior margin of nasal capsule); from A. gabrieli by the presence of acutely furcate caudal fin (vs. smoothly furcate), and dorsolateral body plates on predorsal region touching or closer to their counterparts (vs. dorsolateral body plates more distant from their counterparts); from A. lakoi it can be distinguished by lacking a pointed process on anterodorsal portion of infraorbital 1 (vs. presence); from A. depinnai and A. poecilus plus A. aldebaran , A. belenos , A. kiriri , A. psammatides , A. raimundi , and A. velites by having relatively wide frontal bone, with width equal to or slightly larger than half of entire length (vs. narrow, with width slightly smaller than half of entire length in A. aldebaran , A. belenos , A. depinnai , A. kiriri , A. poecilus , A. raimundi and A. velites ; extremely narrow, with width conspicuously smaller than half of entire length in A. psammatides ); from A. azaghal it differs by the presence of the first dorsal-fin element, the spinelet (vs. absence). It can be further distinguished from A. aldebaran , A. belenos , and A. kiriri by having parapophysis of the complex vertebra poorly or moderately developed (vs. well developed); from A. rochai by having preadipose azygous plates generally with similar sizes; anteriormost plates smaller than remaining plates in some specimens (vs. preadipose azygous plates with variable sizes, alternating between smaller and larger plates).

Description. Morphometric data presented in Tab. 3; additional morphometric data available in Lima, Britto (2001:1012, tab. 1). Head compressed with convex dorsal profile, somewhat triangular or trapezoid in dorsal view. Snout relatively well developed and pointed; or moderately developed and more rounded. Head profile convex from tip of snout to anterior nares; region of mesethmoid slightly concave in some specimens; ascending slightly convex to nearly straight from this point to dorsal-fin origin. Profile slightly convex along dorsal-fin base. Postdorsal-fin body profile slightly concave or nearly straight to adipose-fin spine; slightly concave from this point to caudal-fin base. Ventral profile of body slightly convex from isthmus to pelvic-fin origin; lump on isthmus region in some specimens (apparently by malformation); region of gill opening slightly concave in some specimens; nearly straight from this point to anal-fin origin; 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 dorso-laterally on head; orbit delimited dorsally by lateral ethmoid, frontal and sphenotic, ventrally by infraorbitals. Anterior and posterior nares close to each other, only separated by flap of skin. Anterior naris tubular. Posterior naris close to anterodorsal margin of orbit, separated from it by distance equal to or slightly smaller than naris diameter. Mouth small, subterminal, width larger than bony orbit diameter. Maxillary barbel moderate to large in size, ranging from not reaching to surpassing anteroventral limit of gill opening. Outer mental barbel slightly larger than maxillary barbel. Inner mental barbel fleshy, with base close to its counterpart. Lower lip moderately developed, forming small semicircular or triangular fleshy flap; with two triangular fleshy flaps in some specimens. Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout and isthmus.

Mesethmoid short; anterior tip long, slightly larger than 50% of entire bone length (see Britto, 2003:123, ch. 1, state 0; fig. 1A); posterior portion wide, entirely, or almost entirely covered by thick layer of skin. Nasal slender, curved laterally, inner margin generally with moderately developed laminar expansion; variably poorly developed; outer margin with reduced laminar expansion; absent in some specimens; mesial border generally contacting only frontal; or contacting frontal and mesethmoid.

Frontal elongated, relatively wide, with width equal to or slightly larger than half of entire length ( Fig. 3B ); anterior projection ranging from short, with size smaller than nasal length, to long, with size larger than nasal length; anterior margin generally covered by thick layer of skin. Frontal fontanel relatively small, ellipsoid or somewhat rhomboid; posterior tip extension not entering anterior margin of parieto-supraoccipital. Sphenotic somewhat trapezoid, contacting parieto-supraoccipital dorsally, pterotic-extrascapular posteriorly, second infraorbital ventrally and frontal anteriorly. Pterotic-extrascapular roughly pipe-shaped, with posteriormost portion contacting first lateral-line ossicle, and ventral margin contacting opercle and cleithrum; posterior expansion almost entirely covering lateral opening of swimbladder capsule, leaving slender pseudotympanic area on its dorsal margin covered only by thick layer of skin. Parieto-supraoccipital wide, posterior process strongly reduced to poorly developed; not contacting nuchal plate. Parieto-supraoccipital medial keel expanded ventrally; laminar, with posterior portion at same level as posterior process tip; with posterior portion variably not reaching tip of posterior process; or expanded posteriorly, surpassing tip of posterior process. Parieto-supraoccipital fontanel small, roundish; located medially on parieto-supraoccipital; or slightly displaced towards posterior portion of parieto-supraoccipital; fontanel occluded, reduced to a small fossa, in some specimens.

Two laminar infraorbitals with minute odontodes; infraorbital 1 large, ventral laminar expansion generally ranging from poorly developed to well developed; almost reduced to latero-sensory canal in some specimens; single specimen with extremely well-developed ventral laminar expansion (MZUSP 49853, 35.4 mm SL); anterior portion with laminar expansion ranging from strongly reduced, at same level as posterior margin of nasal capsule, to moderately developed, reaching middle of nasal capsule ( Fig. 12 ); inner laminar expansion ranging from well developed to extremely well developed ( Figs. 5A,B ); small portions of external surface covered by thick layer of skin; infraorbital 2 small, generally slender; slightly more compact in some specimens; generally with posterior laminar expansion moderately developed; variably poorly or relatively well developed; inner laminar expansion ranging from moderately to well developed; posteroventral margin close but not directly contacting posterodorsal ridge of hyomandibula; contacting in some specimens; dorsal tip contacting only sphenotic; external surface partially covered by thick layer of skin; or entirely covered by thick layer of skin ( Fig. 12 ). Posterodorsal ridge of hyomandibula, close to its articulation with opercle, oblong, relatively slender; generally exposed; entirely or almost entirely covered by thick layer of skin in some specimens; dorsal ridge of hyomandibula, between pterotic-extrascapular and opercle, covered by thick layer of skin; variably covered by thin layer of skin, exposed; exposed areas generally bearing small odontodes. Interopercle with posterior portion exposed; or entirely covered by thick layer of skin; somewhat triangular, anterior projection moderately developed; variably well developed. Preopercle relatively slender, elongated, minute odontodes sparse on external surface; entirely or almost entirely covered by thick layer of skin in some specimens. Opercle compact in shape, width larger than half of its length; free margin convex; posterodorsal region variably with smoothly concave area; without serrations and covered by small odontodes; some portions of bony distal margin irregular in some specimens.

Four branchiostegal rays decreasing in size posteriorly. Hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion well developed, about twice size of cartilaginous portion; or conspicuously well developed, about triple size of cartilaginous portion. Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with small process on anterior margin of mesial portion; process strongly reduced in some specimens; ceratobranchial 3 generally with continuous postero-lateral margin; variably notched; ceratobranchial 5 toothed on postero-dorsal surface, 25 to 34 (22) 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 triangular uncinate process on laminar expansion of posterior margin. Two wide pharyngobranchials (3 and 4), pharyngobranchial 3 with triangular laminar expansion on posterior margin; triangular laminar expansion variably with notches. Upper tooth plate oval, with 29 to 42 (22) teeth aligned in two rows on postero-ventral surface.

Lateral-line canal entering neurocranium through pterotic-extrascapular, branching twice before entering sphenotic: pterotic branch with single pore; preoperculomandibular branch conspicuously reduced, with single pore opening close to postotic main canal; more developed, with pore opening closer to anteroventral border of pterotic-extrascapular in some specimens; postotic main canal widens just posterior to pterotic branch. Sensory canal continuing through pterotic-extrascapular, entering sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, another branch entering frontal through supraorbital canal, both with single pore. Supraorbital canal branched, running through nasal bone. Epiphyseal branch of supraorbital canal relatively long, with pore opening close to frontal fontanel; or slightly shorter, with pore opening closer to supraorbital main canal. Nasal canal with three openings, first on posterior edge, second on posterolateral portion and third on anterior edge; second pore generally fused with first pore. Infraorbital canal running through entire second infraorbital, 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 opening at posterodorsal ridge of hyomandibula in some specimens.

Dorsal fin somewhat triangular, located just posterior to third or fourth dorsolateral body plate. Dorsal-fin rays II,7(1), II,8*(23), II,9(1), posterior margin of dorsal-fin spine smooth. Nuchal plate poorly developed in length; strongly reduced in some specimens; generally, entirely covered by thick layer of skin; posterior portion variably exposed and with minute odontodes ( Fig. 13 ); spinelet extremely short or short; partially exposed or entirely covered by thick layer of skin; spine poorly developed, adpressed distal tip reaching middle portion of dorsal-fin base; or moderately developed, adpressed distal tip slightly surpassing middle portion of dorsal-fin base; anterior margin with small odontodes. Pectoral fin roughly triangular, its origin just posterior to gill opening. Pectoral-fin rays I,8(1), I,9*(24); posterior margin of pectoral spine with eight to 24 poorly- or moderately-developed serrations along almost its entire length; small region just posterior to origin of spine lacking serrations; some serrations directed towards origin of spine, perpendicularly directed or directed towards tip of spine; presence of bifid serrations in some specimens; base of branched rays with small laminar expansions on inner margin, generally more evident on first rays; laminar expansions variably with irregular margins ( Fig. 14 ). Anteroventral portion of cleithrum partially exposed; posterolateral portion of scapulocoracoid reduced, generally externally visible, or covered by thick layer of skin, not externally visible. Pelvic fin oblong, located just below fourth or fifth ventrolateral body plate, and at vertical through third dorsal-fin branched ray. Pelvic-fin rays i,5*(25). Adipose fin roughly triangular, separated from posterior origin of dorsal-fin base by nine to 11 dorsolateral body plates. Anal fin somewhat triangular, located just posterior to 13 th, 14 th, or 15 th ventrolateral body plates, and at vertical through region of preadipose platelets; or anterior to region of preadipose platelets. Anal-fin rays ii,6*(25). Caudal-fin rays i,12,i*(24), i,13,i(1), generally five or six dorsal and/or ventral procurrent rays; caudal fin bilobed, dorsal lobe slightly larger than ventral lobe.

Two to four laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, third and fourth lateral-line canals, if present, encased in third and fourth dorsolateral body plates, respectively. Body plates with conspicuous line of relatively large odontodes confined to posterior margins; dorsolateral body plates 26*(4), 27(10), 28(10), 29(1); ventrolateral body plates 23*(2), 24(6), 25(17); dorsolateral body plates along dorsal-fin base 5(2), 6*(16), 7(7); dorsolateral body plates between adipose-fin spine and caudal-fin base 7(2), 8*(14), 9(8), 10(1); preadipose platelets 4(3), 5*(12), 6(7), 7(3), 8(1); 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 of frontal with lateral ethmoid, with small platelets; platelets variably absent. Ventrolateral portion of snout, region of nasal capsule and dorsal portion of snout, above mesethmoid, with small platelets in some specimens. Region between nuchal plate and posterior process of parieto-supraoccipital variably with relatively large platelets. Ventral surface of trunk covered by small platelets, generally more abundant and/or concentrated on anterior half of trunk; absence of platelets in some specimens.

Vertebral count 24(1), 25(11), 26(8), 27(2); ribs 6(2), 7(18), 8(2), first pair conspicuously large; parapophysis of complex vertebra poorly or moderately developed ( Figs. 8B,C ).

Coloration in alcohol. Color pattern highly variable. Ground color of body light or brownish yellow, with top of head dark brown. Posterodorsal portion of head, region below eye, opercle and cleithrum with scattered dark brown or black chromatophores. Snout covered by dark brown or black chromatophores on its dorsal surface; chromatophores densely disposed in some specimens; variably forming dark brown or black rounded, striated or irregular spots; with dark brown or black diffuse stripe from anteroventral portion of orbit to upper lip lateral area in some specimens; ventrolateral portion of snout variably with dark brown or black chromatophores. Upper lip and maxillary barbel with dark brown or black chromatophores; area of lateral portion of upper lip with conspicuous concentration of dark brown or black chromatophores in some specimens; outer mental barbel with dark brown or black chromatophores, generally more evident on its proximal portion, in some specimens; region of isthmus around lower lip variably with dark brown or black chromatophores. Dorsal series of four to five dark brown or black blotches, first on anterior portion of dorsal-fin base, second, if present, on middle portion of dorsal-fin base, third on posterior portion of dorsal-fin base, fourth on adipose-fin base, fifth on caudal-fin base; blotches variably diffuse. Dorsal portion of body with conspicuous concentration of dark brown or black chromatophores between counterparts of dorsolateral body plates in some specimens. Ventral surface of trunk and region posterior to urogenital opening with dark brown or black chromatophores in some specimens. First dorsolateral body plate with conspicuous concentration of dark brown or black chromatophores; posterior margin of some dorso- and ventrolateral plates, and lateral line pores with conspicuous concentration of dark brown or black chromatophores in some specimens. Midline of flank with longitudinal series of three to six medium- to large-sized conspicuous dark brown or black blotches; blotches rounded, oblong or irregular; blotches fused with each other, forming longitudinal stripe in single specimen (DZSJRP 12585, 29.9 mm SL). Dorsal half of dorsolateral body plates with dark brown or black chromatophores; region of anterior and posterior portions of dorsal-fin base, between dorsal and adipose fins, adipose-fin base, between adipose and base of caudal peduncle and base of caudal peduncle with more concentrated chromatophores, forming conspicuous blotches in some specimens; blotches variably fused to flank midline blotches. Ventral half of dorsolateral body plates and dorsal half of ventrolateral body plates with concentration of dark brown or black chromatophores, forming conspicuous blotches in some specimens; blotches generally more evident on anterior portion of body and on area of flank midline blotches. Mid-ventral portion of ventrolateral body plates on area of flank midline blotches with concentration of dark brown or black chromatophores; forming conspicuous blotches in some specimens; blotches generally more evident posteriorly to pelvic-fin origin; variably fused to flank midline blotches; ventral portion of ventrolateral body plates with concentration of dark brown or black chromatophores, generally more evident posterior to anal-fin anterior origin, in some specimens. Dorsal fin with dark brown or black spots; aligned spots, forming longitudinal or oblique bars in some specimens; conspicuous concentration of dark brown or black chromatophores on some areas of membranes, forming larger dark brown or black patches in some specimens; almost entirely solid black or covered by dark brown or black chromatophores in some specimens; dorsal-fin base with conspicuous concentration of dark brown or black chromatophores, generally more concentrated on bases of first and last branched rays; spine covered by dark brown or black chromatophores. Pectoral fin with dark brown or black chromatophores on its dorsal surface, generally more evident on spine and first branched rays; covered by dark brown or black spots in some specimens; spots generally diffuse and more evident on first branched rays; or entirely hyaline; region of body around dorsal portion of pectoral-fin origin generally with concentration of dark brown or black chromatophores. Pelvic fin generally hyaline or with sparse dark brown or black chromatophores on its dorsal surface; with conspicuous concentration of dark brown or black chromatophores on its proximal two thirds or forming up to two oblong dark brown or black patches in some specimens; region of body around dorsal portion of pelvic-fin origin with concentration of dark brown or black chromatophores in some specimens. Adipose-fin membrane with dark brown or black chromatophores; conspicuous concentration of dark brown or black chromatophores in some areas of membrane, generally more evident close to spine, forming isolated patches in some specimens; adipose-fin spine generally with dark brown or black chromatophores. Anal fin with conspicuous concentrations of dark brown or black chromatophores in some areas, generally more evident on its middle portion and bases of last branched rays; with one to three dark brown or black blotches in some specimens; entirely or almost entirely covered by dark brown or black chromatophores in some specimens. Middle portion of caudal-fin base, posteriorly to last flank midline blotch, generally with small- to medium-sized dark brown or black blotch; blotch diffuse or fused with last midlateral blotch in some specimens. Caudal fin with three to six transversal dark brown or black slender to wide bars.

Coloration in life. Similar to that observed in preserved specimens but with ground color of body grayish yellow in some specimens. Body covered by whitish yellow and green iridescent coloration ( Fig. 15 ).

Geographical distribution. Aspidoras albater is known from the upper portions of the Tocantins and Paraná River basins in Goiás State, upper rio Araguaia basin in Goiás and Mato Grosso states, and upper rio Paraguay basin in Mato Grosso State, Brazil ( Fig. 10 ).

Conservation status. Aspidoras albater is widespread in central Brazil, occurring in the Tocantins-Araguaia, Paraná, and Paraguay river basins of Goiás and Mato Grosso states. No threat to the species is currently known. According to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019), Aspidoras albater can be classified as Least Concern (LC).

Remarks. According to Nijssen, Isbrücker (1976), A. albater can be recognized by the presence of four large oblique black blotches on body. As aforementioned (see Color in alcohol), the dark brown or black blotches on dorsal and ventral portions of flanks can be fused to flank midline blotches, resulting in these somewhat oblique, irregular, large blotches. However, this pattern is not present in all type specimens. Among the 10 type specimens re-examined herein for this feature (MZUSP 12991, MZUSP 12992 and USNM 213540, and considering the left side of the body), only the holotype and four paratypes display such a pattern for all midline blotches ( Figs. 11 , 16A,E,F,H ). In the other five paratypes, it was possible to observe that some midline blotches can be variably fused with the blotches on dorsal and/or ventral portions of flanks ( Figs. 16B,C,D ), or even present no fusion with any of them ( Figs. 16C,D,G ). Also, the fusion between midline and ventral blotches often results in large transversally elongated blotches ( Figs. 16B‒D ), whereas the fusion between dorsal, midline and ventral blotches may result in chevron-shaped large blotches instead of the oblique pattern ( Fig. 16 ). Such variable patterns were also observed in several non-type specimens. Therefore, since this feature is highly variable and may be present in other Aspidoras species, such as A. depinnai and A. kiriri , it should not be considered as diagnostic for A. albater .

Aspidoras eurycephalus ( Fig. 17 ) was described from the rio Maranhão basin, also part of the upper rio Tocantins drainage. Comparing only the holotypes, A. albater can be distinguished from A. eurycephalus by presenting the following combination of features: (I) absence of contact between counterparts of dorsolateral body plates on predorsal region of body (vs. presence); (II) posterior process of the parieto-supraoccipital poorly developed (vs. strongly reduced); (III) pectoral spine poorly developed but clearly larger (vs. poorly developed but clearly smaller); (IV) smaller interorbital width (vs. larger); and (V) ventral laminar expansion of infraorbital 1 moderately developed (vs. well developed). Despite the holotypes presenting these remarkable differences, most of the examined specimens from the upper rio Tocantins basin, including even some paratypes of A. albater , present an intermediate morphology or a mix of features found in either the holotype of A. albater or the holotype of A. eurycephalus . Intermediate or mixed morphotypes were also found in the upper portions of the rivers Araguaia, Paraguay, and Paraná basins.

Lima, Britto (2001) described A. taurus ( Fig. 18 ) based on the following diagnostic features: (I) infraorbitals and preopercle covered by thick skin and not visible externally; (II) nuchal plate reduced, covered by thick skin and not visible externally; and (III) absence of lateral line posterior to two small lateral line ossicles. Regarding feature (I), the examination of several specimens from the A. taurus type series, including the holotype, and additional non-type specimens (LBP 1427), revealed that only the infraorbital 2 and preopercle can be entirely covered by thick layer of skin in some specimens, contrary to the infraorbital 1, that is at least partially externally visible in all examined specimens. In some A. taurus specimens, as well as in some A. albater specimens from the rivers Araguaia, Tocantins and Paraná basins, the ventral laminar expansion of infraorbital 1 is almost reduced to the latero-sensory canal, resulting in an extremely small exposed area in those specimens, which is difficult to observe with naked eyes and may cause the wrong perception that the infraorbital 1 is not exposed. Despite the fact that it was possible to confirm the presence of the features (II) and (III) in A. taurus , they can also be observed in A. albater specimens from the rivers Araguaia, Tocantins and Paraná basins.

One of the most remarkable features of A. taurus is the relatively large size of some specimens, reaching more than 50 mm SL, though most specimens present the expected size for the genus, which is generally inferior to 40 mm SL. However, considering general morphological pattern, even these unusually large specimens are notably similar to the holotype of A. eurycephalus and some paratypes of A. albater . Additionally, it is also possible to find relatively large-sized specimens in populations from the rivers Araguaia (LIRP 4472, up to 40.1 mm SL, Fig. 19A ; MZUSP 41409, up to 44.6 mm SL), Tocantins (MZUSP 114391, up to 40.0 mm SL) and Paraná (DZSJRP 9963, up to 41.6 mm SL) basins. Considering each examined feature (e.g., infraorbital 1, predorsal, pectoral spine, interorbital, and color patterns), the holotypes of A. albater A. eurycephalus and A. taurus alternately represented two extreme forms of a morphological range, with one of them, as well as most additional examined specimens, falling in between the other two, and, because no conspicuous diagnostic features were observed, the most reasonable decision is to place both A. eurycephalus and A. taurus in the synonymy of A. albater .

Specimens clearly compatible with A. albater are scarce in the aquarium hobby. However, the species coded as Aspidoras sp. C 35, which is known as “the black phantom” among hobbyists due to its intensely pigmented pattern, especially on dorsal fin, likely represents A. albater . According to Hans Evers (2020, pers. comm.), who captured the specimens originally used to assign the code C35 ( Fig. 15C ), this species was found in a place called “Bacalhau”, a small, shallow, and crystal clear-water stream, while traveling from Aruanã to Goiânia, in Goiás State. Around the middle of the shortest route from Aruanã to Goiânia, on the outskirts of the Goiás Velho City, a small stream called córrego Bacalhau crosses the road GO-070 (15°57’01”S 50°08’52”W). This stream is a tributary to the rio Vermelho, rio Araguaia basin. Considering the presence of A. albater specimens with intensely black pigmentation on dorsal fin, including specimens from the rio Tocantins basin in Goiás ( Fig. 19B ), allied to the compatible geographical distribution, it seems reasonable to conclude that C35 corresponds to A. albater . On the other hand, the species coded as CW52, often attributed to A. albater , presents unknown origin and intermediate morphological and color patterns between A. albater and A. poecilus . It is known that many Aspidoras species that were introduced into the hobby were kept mixed, easily interbreeding with fertile F1 offspring (Robert McLure, 2020, pers. comm.). This may explain C52’s simultaneous similarity to two completely different species such as A. albater and A. poecilus . Therefore, CW52 is considered herein as a possible aquarium strain.

Material examined. In addition to the material examined by Nijssen, Isbrücker (1976), the following material was examined. All from Brazil. Rio Paraguay basin. DZSJRP 12585, 20 of 33, 14.5‒29.9 mm SL, Mato Grosso, stream tributary to the rio Itiquira. LBP 1427, 29, 17.2‒39.5 mm SL, 2 CS, 23.8‒36.7 mm SL, Mato Grosso, rio Itiquira. MZUSP 57154, 52.1 mm SL, holotype of Aspidoras taurus Lima, Britto, 2001 , Mato Grosso, Fazenda Cabeceira do Itiquira, close to highway BR-364, rio Itiquira. MNRJ 19951, 5, 30.9–40.3 mm SL; MZUSP 41455, 228 (5 CS not measured), 14.1‒54.1 mm SL; USNM 363174, 5, 31.5–40.9 mm SL, paratypes of Aspidoras taurus Lima, Britto, 2001 , all collected with holotype. Rio Paraná basin. DZSJRP 9963, 8, 24.3‒41.6 mm SL, Distrito Federal, córrego Vicente Pires. MNRJ 19984, 1, 35.6 mm SL, Distrito Federal, stream tributary to the lago Paranoá. MNRJ 20258, 3, 14.3‒36.8 mm SL, Goiás, córrego Coqueiro. MNRJ 20332, 2, 26.9‒29.7 mm SL, Goiás, córrego Águas Emendadas. MZUSP 41434, 8, 9.8‒21.1 mm SL, Goiás, ribeirão Capivara. NUP 1098, 5, 20.2‒39.7 mm SL, 1 CS, 33.8 mm SL, Goiás, Corumbá Reservoir. NUP 1286, 2, 19.7‒27.9 mm SL, Goiás, ribeirão Cachoeira. Rio Araguaia basin. DZSJRP 19858, 23, 21.9‒37.9 mm SL, Mato Grosso, córrego Fundo II. LBP 15657, 1, 22.2 mm SL, Mato Grosso, tributary to the rio das Mortes. LIRP 4447, 5, 14.9‒25.8 mm SL, 1 CS, 29.4 mm SL, Mato Grosso, córrego Rico. LIRP 4472, 85 of 162, 20.4‒40.1 mm SL, 3 CS of 162, 29.4‒31.9 mm SL, Mato Grosso, córrego Carneiro. MNRJ 21075, 17, 14.7‒28.2 mm SL, 2 CS, 25.0‒ 25.9 mm SL, Mato Grosso, stream tributary to the rio das Garças. MZUSP 28599, 29, 13.8‒36.4 mm SL, Mato Grosso, rio Noidore. MZUSP 41409 , 131 , 12.1–44.6 mm SL, Goiás , grotto on the road to Couto de Magalhães Falls. MZUSP 41424, 7, 14.5‒33.9 mm SL, Goiás, córrego do Jacaré. MZUSP 88144, 2, 23.0‒ 34.4 mm SL, Mato Grosso, tributary to the rio das Garças. MZUSP 89424, 2, 25.2‒27.3 mm SL, Goiás, ribeirão d’Anta. MZUSP 97858, 10 of 23, 13.3‒27.3 mm SL, Mato Grosso, unnamed stream. UFRJ 6434, 13, 16.8‒28.5 mm SL, Goiás, stream tributary to the rio Caiapó. Rio Tocantins basin. INPA 39901, 10 of 91, 17.4‒19.3 mm SL, Goiás, rio Areia. LBP 15302, 2, 28.3‒33.4 mm SL, Goiás, rio da Lapa. LBP 19277, 8, 24.8‒35.4 mm SL, Goiás, córrego Kavanca. LBP 19312, 1, 27.6 mm SL, Goiás, unnamed stream. LESCI 334, 1, 32.7 mm SL, Goiás, Angélica Cave. LISDEBE 6606, 24.7 mm SL, Goiás, unnamed stream. MCP 45556, 6, 18.7‒24.2 mm SL, Goiás, córrego Galheiros. MNRJ 11716, 66 of 69, 16.0‒ 29.6 mm SL, 3 CS of 69, 26.7‒29.9 mm SL, Goiás, córrego Pontilhão. MNRJ 12564, 6, 24.3‒34.7 mm SL, Goiás State, ribeirão do Padre. MNRJ 12571, 10 of 26, 22.2–33.4 mm SL, 1 CS of 26, 35.3 mm SL, Goiás, stream tributary to the rio Tocantins. MNRJ 12581, 39 of 44, 14.6‒29.7 mm SL, 5 CS of 44, 22.5‒31.1 mm SL, Goiás, stream tributary to the rio Tocantins. MNRJ 12725, 3, 25.0‒ 27.3 mm SL, Goiás, córrego Batéias. MNRJ 12766, 1, 23.4 mm SL, Goiás, rio da Mula. MNRJ 12775, 3, 14.5‒25.5 mm SL, Goiás, stream tributary to the rio Tocantins. MNRJ 12779, 8 of 12, 27.4‒28.8 mm SL, 4 CS of 12, 26.2–31.3 mm SL, Goiás, córrego Bateinha. MNRJ 13044, 2, 18.5‒32.9 mm SL, Goiás, córrego Quineira or Mangueira. MNRJ 13045, 34 of 36, 16.6‒25.6 mm SL, 2 CS of 36, 24.0‒ 29.3 mm SL, Goiás, córrego Batéias. MNRJ 13050, 25 of 28, 19.0‒ 29.9 mm SL, 3 CS of 28, 17.6‒32.5 mm SL, Goiás, córrego Pontilhão. MNRJ 13051, 1, 20.9 mm SL, Goiás, córrego Pirapitinga. MNRJ 13052, 5, 27.7‒32.2 mm SL, 1 CS, 36.5 mm SL, Goiás, córrego Grota Seca. MNRJ 13053, 3, 28.1‒37.4 mm SL, Goiás, tributary to the córrego Lageado. MNRJ 13054, 20, 14.0‒ 26.6 mm SL, Goiás, córrego Batéias. MNRJ 13055, 4, 20.2‒36.0 mm SL, 1 CS, 27.2 mm SL, Goiás, Matula Stream. MNRJ 13056, 9, 19.3‒29.8 mm SL, Goiás, stream tributary to the córrego Lageado. MNRJ 13080, 8 of 9, 10.4‒34.7 mm SL, 1 CS of 9, 30.9 mm SL, Goiás, córrego São Bento. MNRJ 13081, 2, 28.4‒33.0 mm SL, Goiás, stream tributary to the córrego São Bento. MNRJ 13082, 6, 15.2‒29.5 mm SL, Goiás, córrego Quineira or Mangueira. MNRJ 28880, 8, 22.7‒32.9 mm SL, Goiás, córrego Água Boa. MNRJ 28881, 3, 25.7‒26.7 mm SL, Goiás, córrego Batéia. MNRJ 36166, 9, 26.5‒33.4 mm SL, Goiás, córrego Água Boa. MZUSP 40624, 4, 23.7‒30.1 mm SL, Goiás, rio Angélica. MZUSP 40656, 2, 19.4‒24.8 mm SL, Goiás, rio Preto. MZUSP 40683, 1, 28.8 mm SL, Goiás, rio Bezerra. MZUSP 40793, 45 of 46, 14.8‒33.5 mm SL, 1 CS of 46, 29.4 mm SL, Goiás, stream tributary to the rio das Almas. MZUSP 40799, 7, 23.3‒28.5 mm SL, Goiás, swamp tributary to the córrego Ave Maria. MZUSP 40806, 3, 21.8‒27.2 mm SL, Goiás, stream tributary to the córrego Ave Maria. MZUSP 40811, 74, 21.2‒32.9 mm SL, Goiás, stream tributary to the córrego Ave Maria. MZUSP 40815, 2, 21.3‒28.3 mm SL, Goiás, stream tributary to the rio das Pedras. MZUSP 40886, 5, 21.6‒35.9 mm SL, Goiás, córrego Poço Danta. MZUSP 49853, 5, 17.0‒ 35.4 mm SL, Goiás, stream in the Serra da Mesa. MZUSP 50157, 35, 11.3‒31.3 mm SL, Goiás, Serra da Mesa Lake. MZUSP 54468, 100, 21.1‒35.4 mm SL, Goiás, rio Bagagem. MZUSP 55221, 56, 14.7‒31.8 mm SL, Goiás, rio da Lapa. MZUSP 55238, 6, 16.8‒23.4 mm SL, Goiás, rio da Lapa. MZUSP 55244, 1, 25.2 mm SL, Goiás, rio Angélica. MZUSP 55250, 1, 26.0 mm SL, Goiás, rio Angélica. MZUSP 55967, 9, 18.7‒28.0 mm SL, Goiás, rio da Lapa sinkhole. MZUSP 55983, 2, 26.6‒27.1 mm SL, Goiás, córrego Quilombo. MZUSP 55985, 1, 25.3 mm SL, Goiás, lapa Angélica. MZUSP 57407, 16, 15.9‒23.1 mm SL, Goiás, stream tributary to the rio São Domingos. MZUSP 81661, 1, 33.0 mm SL, Goiás, rio Angélica. MZUSP 81662, 1, 27.1 mm SL, Goiás, lapa Angélica. MZUSP 85771, 5, 18.2‒27.9 mm SL, Goiás, rio da Lapa. MZUSP 114074, 3, 15.6‒23.2 mm SL, Goiás, ribeirão dos Bois. MZUSP 114080, 2, 25.9–30.2 mm SL, Goiás, stream tributary to the rio dos Bois. MZUSP 114082, 12, 20.1‒32.7 mm SL, Goiás, stream tributary to the rio dos Bois. MZUSP 114089, 4, 16.2‒29.5 mm SL, Goiás, rio São João. MZUSP 114128, 5, 19.6‒26.2 mm SL, Tocantins, córrego Bezerra. MZUSP 114300, 15, 18.0‒ 30.6 mm SL, Goiás, stream tributary to the rio Galheiros. MZUSP 114357, 7, 22.2‒29.4 mm SL, Goiás, rio Muquém. MZUSP 114372, 4, 22.4‒30.8 mm SL, Goiás, stream tributary to the rio Claro. MZUSP 114391, 64, 13.2‒40.0 mm SL, Goiás, tributary to the rio das Almas. MZUSP 114398, 18, 16.2‒28.7 mm SL, Goiás, stream tributary to the rio Paranã. MZUSP 114401, 20 of 21, 20.3‒35.9 mm SL, 1 CS of 21, 30.1 mm SL, Goiás, stream tributary to the rio Paranã. UNT 10233, 5, 14.6‒21.5 mm SL, Goiás, rio do Peixe. UNT 14686, 14, 12.6‒33.2 mm SL, Goiás, córrego Grotão or Maria Rita. UFBA 8077, 6 of 11, 19.4‒30.1 mm SL, Goiás, stream tributary to the rio das Almas. UNT 10225, 6, 8.8‒24.4 mm SL, Goiás, rio Buritizal.

Figures

FIGURE 3 | Dorsal view of the head of CS specimens showing the three patterns of paired frontal bones (outlined in black) in Aspidoras: (A) narrow, with width of each frontal slightly smaller than half of its entire length (Aspidoras maculosus, UFBA 3291, 30.7 mm SL), (B) relatively wide, with width equal to or slightly larger than half of entire length (Aspidoras albater, MZUSP 40793, 29.4 mm SL), and (C) extremely narrow, with width clearly smaller than half of entire length (Aspidoras psammatides, UNT 9604, 27.3 mm SL). Scale bars = 1 mm.

FIGURE 5 | Dorsal view of the infraorbital series of CS specimens showing the four patterns of size and shape of the inner laminar expansion of infraorbital 1 (white arrows) in Aspidoras: (A) extremely well developed (Aspidoras albater, MNRJ 13080, 30.9 mm SL), (B) well developed (Aspidoras fuscoguttatus, NUP 12677, 36.1 mm SL), (C) moderately developed (Aspidoras poecilus, UNT 6249, 30.9 mm SL), and (D) poorly developed (Aspidoras psammatides, UNT 9604, 27.3 mm SL). Abbreviations: io1: infraorbital 1, io2: infraorbital 2. Scale bars = 1 mm.

FIGURE 8 | Ventral view of the complex vertebra in CS specimens of (A) Aspidoras belenos, paratype, UFRJ 4419 (ex-UFRJ 3861), 22.1 mm SL, with well-developed parapophysis, (B) Aspidoras albater, MNRJ 12571, 35.3 mm SL, with poorly-developed parapophysis, and (C) Aspidoras albater, MNRJ 12581 (disarticulated, indeterminate size), with moderately-developed parapophysis. Abbreviations: ccv: centrum of the complex vertebra, pcv: parapophysis of the complex vertebra. Scale bars = 1 mm.

FIGURE 10 | Map showing the geographical distribution of Aspidoras albater (type locality: red circle; non-type localities: black circles), A. aldebaran (type locality: red star; non-type localities: white stars), A. azaghal (purple triangle), A. belenos (type locality: purple diamond), A. brunneus (possible region of type locality: grey diamond), A. carvalhoi (type locality: purple circle), A. depinnai (type locality: red square; nontype localities: black squares), A. fuscoguttatus (type locality: red triangle; non-type localities: white triangles), A. gabrieli (type locality: red pentagon; non-type locality: white pentagon), A. kiriri (black cross), A. lakoi (type locality: red diamond; non-type locality: black diamond), A. maculosus (red cross), and A. mephisto (type locality: white cross). Each symbol may represent more than one locality.

FIGURE 11 | Aspidoras albater, holotype, MZUSP 12991, 34.2 mm SL, rio Tocantinzinho near São João da Aliança, Goiás State, Brazil. Dorsal (top), lateral (middle) and ventral (bottom) views. Photo in lateral view by Eduardo Baena.

FIGURE 12 | Lateral view of the head of CS specimens of Aspidoras albater, showing the patterns of infraorbitals within the species. Ventral laminar expansion of infraorbital 1 strongly reduced in (A) and (B) (LBP 1427, 36.7 mm SL and LIRP 4447, 29.4 mm SL, respectively), poorly developed in (C) (MNRJ 11716, 27.8 mm SL), moderately developed in (D) (MZUSP 40793, 29.4 mm SL) and well developed in (E) (MNRJ 13050, 31.3 mm SL). Abbreviations: io1: infraorbital 1, io2: infraorbital 2, sph: sphenotic, pes: pteroticextrascapular. Scale bars = 1 mm.

FIGURE 13 | Aspidoras albater, MZUSP 40793, CS, 29.4 mm SL, showing predorsal region of trunk in dorsal view. Dotted lines indicate the limits of the tip of the posterior process of the parieto-supraoccipital and anterior tip of the nuchal plate. Abbreviations: np: nuchal plate, pso: parieto-supraoccipital. Scale bar = 1 mm.

FIGURE 14 | Dorsal view of pectoral spines in CS specimens of Aspidoras albater, showing variation in the morphology of pectoral-fin spine: presence of laminar expansion and simple and/or bifid poorly- and/or moderately-developed serrations on its posterior margin in (A) and (B) (MZUSP 114401, 30.1 mm SL and MNRJ 13080, 30.9 mm SL, respectively), (C) with only simple poorly-developed serrations on its posterior margin (LIRP 4472, 29.4 mm SL), (D) with only simple and/or bifid poorly-developed serrations on its posterior margin (MNRJ 12779, 31.3 mm SL), or (E) with only simple and/or bifid moderatelydeveloped serrations on its posterior margin (MNRJ 12581, 31.1 mm SL). Arrows in (A) indicate the small laminar expansions at the base of branched rays. Scale bars = 1 mm.

FIGURE 15 | Aspidoras albater specimens photographed alive. (A) uncataloged aquarium specimen from the rio Araguaia basin, (B) specimen from the rio Muquém, rio Tocantins basin (MZUSP 114357, not measured), (C) uncatalogued aquarium specimens from the rio Araguaia basin, (D) uncatalogued aquarium specimen from Mato Grosso, possibly from the rio Paraguay basin, and (E) specimen from a stream with unknown name tributary to the rio Tocantins basin (LBP 19312, 27.6 mm SL). Photos by Ingo Seidel (A), José Birindelli (B), Hans Evers (C, D), and Martin Taylor (E).

FIGURE 16 | Paratypes of Aspidoras albater, (A–D) MZUSP 12992, 4, 25.9–31.2 mm SL, and (E–I) USNM 213540, 5, 26.1–31.2 mm SL, showing general morphological and color patterns in lateral view. Scale bars = 5 mm.

FIGURE 17 | Holotype of Aspidoras eurycephalus, junior synonym of Aspidoras albater, CAS 16010, 29.5 mm SL, córrego Vermelho into rio das Almas, Goiás State, Brazil. Dorsal (top), lateral (middle) and ventral (bottom) views. Photo by the California Academy of Sciences.

FIGURE 18 | Holotype of Aspidoras taurus, junior synonym of Aspidoras albater, MZUSP 57154, 52.1 mm SL, rio Itiquira, Mato Grosso State, Brazil. Dorsal (top), lateral (middle) and ventral (bottom) views. Photo in lateral view by Eduardo Baena.

FIGURE 19 | Relatively large specimen of (A) Aspidoras albater, LIRP 4472, 40.1 mm SL, and darker specimen of (B) Aspidoras albater, MZUSP 114401, 35.9 mm SL, showing general morphological and color patterns in lateral view. Photo (A) by Celso Ikedo.