Aspidoras poecilus 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 : 96-112

Aspidoras poecilus Nijssen & Isbrücker, 1976

( Fig. 50 )

Aspidoras poecilus Nijssen & Isbrücker, 1976:121 (original description; type locality: creek upstream Porori Village , left bank of the rio Xingu , Mato Grosso State, Brazil). — Reis , 2003:292 (listed). — Ferraris , 2007:109 (listed). — Oliveira et al., 2017:e160118[3] (morphological comparison; partim). — Tencatt, Bichuette, 2017:8 (morphological comparison).

Aspidoras microgalaeus Britto, 1998:361 (original description; type locality: creek at Primavera do Leste- Paranatinga road, Mato Grosso State, Brazil; new synonym). — Reis , 2003:292 (listed). — Ferraris , 2007:109 (listed). — Lima, Britto, 2001:1015 (listed as comparative material). — Leão et al., 2015:578 (morphological comparison). — Tencatt, Bichuette, 2017:21 (listed as comparative material).

Aspidoras marianae Leão, Britto & Wosiacki, 2015:578 (original description; type locality: unnamed stream tributary to the rio Curuá , Pará State , Brazil; new synonym). — Oliveira et al., 2017:e160118[3] (morphological comparison). — Tencatt, Bichuette, 2017:8 (morphological comparison).

Diagnosis. Aspidoras poecilus can be distinguished from its congeners, with exception of A. albater , A. aldebaran , A. azaghal , A. belenos , A. depinnai , A. fuscoguttatus , A. kiriri , A. maculosus , A. mephisto , and A. raimundi , by having inner laminar expansion of infraorbital 1 ranging from moderately to well developed (vs. extremely well developed in A. gabrieli and A. lakoi ; poorly developed in A. psammatides and A. velites ); from A. albater , A. azaghal , and A. mephisto plus A. gabrieli , A. lakoi , A. psammatides , and A. rochai by having a narrow frontal bone, with width slightly smaller than half of entire length (vs. relatively wide, with width equal to or slightly larger than half of entire length in A. albater , A. azaghal , A. gabrieli , A. lakoi , A. mephisto , and A. rochai ; extremely narrow, with width conspicuously smaller than half of entire length in A. psammatides ); from A. aldebaran , A. belenos , and A. kiriri by the presence of parapophysis of the complex vertebra moderately developed (vs. well developed); it differs from A. depinnai by the presence of the following combination of features: dark brown or black stripe from anteroventral portion of orbit to upper lip lateral area generally present and more evident (vs. stripe, when present, less evident), and flanks generally with more numerous and/or evident dark brown or black markings, not considering the number of blotches in the series along flank midline (vs. flanks generally with fewer and/or less evident markings); from A. fuscoguttatus it differs by having the following combination of features: inner laminar expansion of infraorbital 1 generally moderately developed (vs. generally well developed), flanks with clearly less dark brown or black markings, not considering the number of blotches in the series along flank midline (vs. clearly more markings), and generally more evident dark brown or black stripe from anteroventral portion of orbit to upper lip lateral area (vs. generally less evident); from A. maculosus by the following combination of features: dark brown or black stripe from anteroventral portion of orbit to upper lip lateral area generally present and more evident (vs. generally absent, and, when present, less evident), and by dark brown or black large patches on dorsal fin generally present (vs. generally absent); and from A. raimundi by presenting the following combinations of features: dorsal fin generally with small dark brown or black small spots (vs. generally lacking small spots), and markings on ventrolateral body plates generally more numerous and more evident, not considering the number of blotches in the series along flank midline (vs. markings, when present, generally fewer and less evident).

Description. Morphometric data presented in Tab. 8. Head compressed with convex dorsal profile; somewhat triangular or trapezoid in dorsal view. Snout moderately developed and relatively rounded; snout variably short or more pointed. Head profile convex from tip of snout to anterior nares; region of mesethmoid, frontal and/or parieto-supraoccipital 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; 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 ranging from slightly smaller to slightly larger 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 ranging from short, slightly smaller than 50% of entire bone length, to long, slightly larger than 50% of entire bone length; posterior portion wide, generally entirely covered by thick layer of skin; partially exposed in some specimens. Nasal slender, curved laterally, inner margin generally with moderately-developed laminar expansion; poorly developed in some specimens; outer margin with reduced laminar expansion; variably more developed; mesial border contacting only frontal; or contacting frontal and mesethmoid.

Frontal elongated, relatively wide, with width slightly smaller than half of entire length ( Fig. 3A ); anterior projection ranging from short, with size slightly smaller than nasal length, to long, with size larger than nasal length; anterior margin partially or entirely 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 ranging from poorly developed to moderately developed; not contacting nuchal plate. Parieto-supraoccipital medial keel expanded ventrally; laminar, with posterior portion at same level as posterior process tip; or expanded posteriorly, slightly surpassing tip of posterior process; posterior portion variably not reaching tip of posterior process. Parieto-supraoccipital fontanel small, roundish; located medially on 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 well developed to strongly well developed; poorly or moderately developed in some specimens; anterior portion with laminar expansion ranging from poorly developed, slightly surpassing posterior margin of nasal capsule, to extremely well developed, reaching anterior margin of nasal capsule ( Fig. 51 ); inner laminar expansion generally moderately developed ( Fig. 5C ); single specimen with well-developed inner laminar expansion (LIRP 3972, 32.7 mm SL) ( Fig. 5B ); small portions of external surface covered by thick layer of skin; infraorbital 2 small, slender; generally with posterior laminar expansion poorly to moderately developed; relatively well developed in specimen UNT 6234 (38.8 mm SL); inner laminar expansion poorly to moderately developed; posteroventral margin contacting posterodorsal ridge of hyomandibula; close but not directly contacting in some specimens; dorsal tip generally contacting only sphenotic; contacting sphenotic and pterotic-extrascapular in specimen UNT 6234 (38.8 mm SL); small portions of external surface covered by thick layer of skin ( Fig. 51 ). Posterodorsal ridge of hyomandibula, close to its articulation with opercle, oblong, relatively slender; exposed; dorsal ridge of hyomandibula, between pterotic-extrascapular and opercle, generally covered by thin layer of skin, exposed; or covered by relatively thick layer of skin, externally visible; or covered by thick layer of skin, not externally visible; exposed areas generally bearing small odontodes. Interopercle with posterior portion exposed; or entirely covered by thick layer of skin; or almost entirely exposed; somewhat triangular, anterior projection generally moderately developed; poorly developed in specimen UNT 12056 (CS, 31.5 mm SL). Preopercle relatively slender, elongated, minute odontodes sparse on external surface. 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. 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 with continuous postero-lateral margin; ceratobranchial 5 toothed on postero-dorsal surface, 21 to 33 (8) 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; process strongly reduced in some specimens; 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; two triangular expansions in some specimens. Upper tooth plate oval, with 26 to 37 (8) 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 moderately to well developed, with pore opening closer to anteroventral border of pterotic-extrascapular; or conspicuously reduced, with pore opening close to postotic main canal; 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 generally relatively long, with pore opening close to frontal fontanel. Nasal canal with three openings, first on posterior edge, second on posterolateral portion and third on anterior edge; second pore fused with first pore in some specimens. Infraorbital canal running through entire second infraorbital, extending to infraorbital 1 and opening into two or three pores. Preoperculomandibular branch giving rise to preoperculomandibular canal, which runs through entire preopercle with three openings, leading to pores 3, 4, and 5, respectively; pore 3 opening at posterodorsal ridge of hyomandibula in some specimens.

Dorsal fin somewhat triangular, located just posterior to third dorsolateral body plate. Dorsal-fin rays II,7(2), II,8(37), II,9(1) posterior margin of dorsal-fin spine smooth; single specimen with three small serration-like structures (LBP 15860, 1 CS, 26.2 mm SL). Nuchal plate poorly to moderately developed in length; posterior portion exposed and with minute odontodes; anterior tip covered by thick layer of skin; almost entirely exposed in some specimens ( Fig. 52 ); spinelet extremely short or short; partially exposed; spine ranging from poorly developed, with adpressed distal tip reaching middle portion of dorsal-fin base, to relatively well developed, with adpressed distal tip slightly surpassing posterior origin 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(37), I,8,i(1), I,9(2); posterior margin of pectoral spine with 12 to 25 moderatelyto well-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. 53 ). Anteroventral portion of cleithrum partially exposed; posterolateral portion of scapulocoracoid reduced, externally visible. Pelvic fin oblong, located just below third, fourth or fifth ventrolateral body plate, and at vertical through second or third dorsal-fin branched ray. Pelvic-fin rays i,5 (40). Adipose fin roughly triangular, separated from posterior origin of dorsal-fin base by seven to nine dorsolateral body plates. Anal fin somewhat triangular, located just posterior to 12 th, 13 th or 14 th ventrolateral body plates, and at vertical through region of preadipose platelets. Anal-fin rays ii,5(2), ii,5,i(7), ii,6(31). Caudal-fin rays i,12,i(40), five to seven dorsal and/or ventral procurrent rays; caudal fin bilobed, lobes with similar size; dorsal lobe variably slightly larger than ventral lobe.

Two to five laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, third, fourth and fifth lateral-line canals, if present, encased in third, fourth and fifth dorsolateral body plates, respectively. Body plates with conspicuous line of relatively large odontodes confined to posterior margins; dorsolateral body plates 24(6), 25(26), 26(7), 28(1); ventrolateral body plates 21(3), 22(21), 23(15), 25(1); dorsolateral body plates along dorsal-fin base 6(37), 7(3); dorsolateral body plates between adipose-fin spine and caudal-fin base 7(17), 8(21), 9(2); preadipose platelets 3(12), 4(13), 5(10), 6(3), 7(2); 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 small to relatively large platelets ( Fig. 52B ). Ventral surface of trunk densely covered by small irregular platelets; more sparse platelets in some specimens.

Vertebral count 23(5), 24(3); ribs 6(7), first pair conspicuously large; parapophysis of complex vertebra moderately developed ( Fig. 8C ).

Coloration in alcohol. 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; generally, with relatively large rounded or irregular black blotches on top of head. Snout covered by dark brown or black chromatophores on its dorsal surface; chromatophores densely disposed in some specimens; generally forming dark brown or black rounded, striated or irregular spots; generally, with dark brown or black diffuse or conspicuous stripe from anteroventral portion of orbit to upper lip lateral area; ventrolateral portion of snout with dark brown or black chromatophores, variably forming spots, in some specimens; spots variably diffuse or absent. Upper lip and maxillary barbel with dark brown or black chromatophores; area of lateral portion of upper lip generally with conspicuous concentration of dark brown or black chromatophores; 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 three to five dark brown or black blotches, first on anterior portion of dorsal-fin base, second on posterior portion of dorsal-fin base, third on adipose-fin base, fourth, if present, on middle portion of caudal peduncle, and fifth, if present, 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 variably with dark brown or black chromatophores. 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 four to six medium- to large-sized conspicuous dark brown or black blotches; blotches rounded, oblong or irregular; blotches fused with each other, forming larger longitudinally elongated blotch in some specimens. Dorsal half of dorsolateral body plates with dark brown or black chromatophores; region of anterior and posterior portions of dorsal-fin base, adipose-fin base, and base of caudal peduncle generally with more concentrated chromatophores, forming conspicuous blotches in some specimens. 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; variably forming conspicuous blotches; blotches generally more evident posteriorly to pelvic-fin origin; 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 small spots; spots longitudinally or obliquely aligned, forming bars in some specimens; variably with two rows of aligned spots; or non-aligned spots; with conspicuous concentration of dark brown or black chromatophores on some areas of membranes, mainly on anterior portion of fin, forming larger dark brown or black patches in some specimens; small spots variably absent, with large dark brown or black conspicuous blotch on middle portion of fin 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; region of body around dorsal portion of pectoral-fin origin with concentration of dark brown or black chromatophores in some specimens. Pelvic fin with dark brown or black chromatophores on its dorsal surface; or hyaline. 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 or two dark brown or black blotches 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 variably diffuse or fused with last midlateral blotch. 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. 54 ).

Geographical distribution. Aspidoras poecilus is known from the rio Araguaia basin in Mato Grosso, rio Tocantins basin in Goiás and Tocantins states, rio Tapajós basin in Mato Grosso State, and rio Xingu basin in Mato Grosso and Pará states, Brazil ( Fig. 55 ) .

Conservation status. Aspidoras poecilus is a widespread species, ocurring in the Tocantins-Araguaia , Tapajós and Xingu river basins, at the states of Goiás, Mato Grosso, Pará and Tocantins, central and northern Brazil. Additionally , 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 poecilus can be classified as Least Concern (LC).

Remarks. Aspidoras poecilus was originally described from the rio Xingu basin, in

Mato Grosso State, and from the rio Araguaia basin, in Goiás State. Despite Nijssen,

Isbrücker (1976:121) statement that the type locality of this species is a tributary to the rio Xingu near the border Mato Grosso-Pará, Leão et al. (2015:583) discussed a possible error regarding this information, since only the holotype was collected there, whereas the paratypes and additional non-type specimens are all from the rio Araguaia basin .

Other records of A. poecilus in the rio Xingu basin were unknown until then. However,

the material examined herein resulted in the discovery of a single specimen collected in the region of the type locality in 2008 ( MNRJ 33855 ), which in fact fits the holotype .

Considering this, there is no plausible reason to refute the type locality provided by

Nijssen, Isbrücker (1976). Additionally, the analysis of the material gathered herein,

including specimens from the Tocantins-Araguaia system, rio Xingu, and rio Tapajós basins, allowed the recognition of A. microgalaeus and A. marianae as synonyms of A.

poecilus, not only confirming the records provided by Nijssen, Isbrücker (1976) but significantly widening the geographic distribution of this species. Both synonymies and the new records are explained below.

Based on the holotype and this single additional specimen, it was possible to observe some osteological features of the typical A. poecilus , characterized by ventral laminar expansion of infraorbital 1 well developed, posterior margin of pectoral spine with moderately-developed serrations, and nuchal plate with anterior tip relatively close to posterior tip of the parieto-supraoccipital. This general morphological pattern can be observed in most specimens from the rio Araguaia basin, but with some specimens presenting ventral laminar expansion of infraorbital 1 poorly developed (LBP 4019, in one of the 18 examined), moderately developed (LBP 4019, in one of the 18 examined) or strongly developed (LBP 20797, in two of the 14 examined, and LBP 4019, in five of the 18 examined). In general, the color pattern of the typical A. poecilus is also observed in specimens from the rio Araguaia basin, except for the presence of some specimens with anterior portion of dorsal fin with concentration of dark brown or black chromatophores and/or non-aligned spots on dorsal fin ( Fig. 56A ). Since most specimens present the osteological pattern of the typical A. poecilus , including individuals with or without the typical dorsal-fin color pattern, and considering that the ventral laminar expansion of infraorbital 1 presents a gradative variation, ranging from poorly to strongly well developed but with two intermediary stages (moderately and well developed), there is no plausible reason to consider the populations from the rio Araguaia basin as a distinct species.

Britto (1998) described Aspidoras microgalaeus ( Fig. 57 ) from a tributary to the rio Culuene, itself a tributary to the upper rio Xingu basin in Mato Grosso State. The analysis of several specimens from this region, including type material, revealed some incongruences between the examined material and the information provided in the original description. According to Britto (1998:362, fig. 4b), there is a relatively large distance between nuchal plate and posterior tip of parieto-supraoccipital, which was initially considered one of the diagnostic features between A. microgalaeus and A. poecilus . However, the analysis of CS specimens revealed some variation in such feature, as both structures are clearly closer to each other in some individuals.

Another diagnostic feature assigned by Britto (1998:364) is the number of preadipose plates (5–6; cited as “scutes” in that paper). Those counts are completely nested in the range observed herein for A. poecilus (3–7). Britto (1998:364) also used vomer morphology (bifurcated anterior portion vs. anterior portion with a unique process) in his diagnosis. Such feature could not be extensively checked in this review due to the difficulty in clearly delimiting the suture between vomer and mesethmoid in part of the analyzed material. However, a bifurcated anterior portion of the vomer could be observed in at least two specimens of A. poecilus , one from the rio Xingu basin (CPUFMT 2060, 27.6 mm SL), and another one from the rio Tocantins basin (UNT 5548, 23.0 mm SL), which refutes such feature as diagnostic between A. microgalaeus and A. poecilus .

In the original description, the infraorbital 1 of A. microgalaeus was depicted with a moderately-developed ventral laminar expansion and a poorly developed anterior laminar expansion (see Britto, 1998:363, fig. 5b). Even though most specimens present ventral laminar expansion of infraorbital 1 moderately developed, specimens with poorly- or well-developed expansions are also present, overlapping with the range for A. poecilus . Regarding the anterior portion of the infraorbital 1, it was also possible to observe some degree of variation, which ranged from poorly developed to moderately developed. Although typical A. poecilus generally presents anterior laminar expansion of infraorbital ranging from well developed to extremely well developed, some specimens from the rio Araguaia basin displayed a moderately-developed expansion, and therefore it cannot be considered as a diagnostic feature. Also, as observed in typical A. poecilus , most specimens of A. microgalaeu s present inner laminar expansion of infraorbital 1 moderately developed, with the exception of a single specimen (LIRP 3972, 32.7 mm SL), which presents a well-developed expansion.

The pectoral-fin spine of A. microgalaeus was also illustrated by Britto (1998:363, fig. 6a), displaying moderately-developed serrations on its posterior margin. As typically seen in A. poecilus , most examined specimens of A. microgalaeus indeed present moderately developed serrations ( Fig. 53A ), although some specimens present well-developed serrations ( Fig. 53B ). At last, the unique morphological feature provided in the original description (see Britto, 1998:364) that could be used to differ A. microgalaeus from A. poecilus is the vertebral count (25, excluding those five from the Weberian apparatus, as considered in that paper vs. 23–24). Notwithstanding, some species of Aspidoras have a variation range on vertebral count equal to (23 to 25 in A. fuscoguttatus and A. raimundi ) or even greater (24 to 27 in A. albater ) than that, which suggests that this feature alone should not be considered robust enough to distinguish A. microgalaeus from A poecilus .

Regarding color pattern, Britto (1998:367) stated that A. microgalaeus presents five to six blotches along midline of flank, but some paratypes (see Britto, 1998:365, fig. 8) and non-type specimens present four blotches, similar to what is observed in the typical A. poecilus (left and right sides of the holotype with four and five blotches, respectively, and four blotches in both sides of specimen of MNRJ 33855). Also, as in A. poecilus , many specimens of A. microgalaeus present dorsal fin with longitudinally or obliquely aligned spots, with concentration of dark brown or black chromatophores on membranes, forming longitudinal or oblique bar ( Fig. 54C ). In general, the only difference related to color pattern between the two species is that some specimens of A. microgalaeus present a densely mottled body ( Fig. 54C ), contrary to the typical A. poecilus , that presents a less mottled pattern ( Figs. 50 , 54A,B,D , 56 ). However, considering that most features related to both osteological and color patterns presented overlap, and no conspicuous diagnostic features were observed, A. microgalaeus is placed in the synonymy of A. poecilus .

Aspidoras marianae Leão, Britto & Wosiacki, 2015 was described from the rio Curuá basin, a tributary to the rio Xingu basin in Pará State. According to its original description (Leão et al., 2015:578), this species can be distinguished from all congeners by having small odontode-bearing platelets on snout. In perspective, this feature was also variably observed in A. albater , A. belenos , A. fuscoguttatus , A. poecilus , A. psammatides , and A. raimundi , and is thus not diagnostic among congeners. The authors also stated that the species can be distinguished from its congers, except A. taurus , by having infraorbitals covered by thick layer of skin, not externally visible, and from A. taurus by having small platelets on the region between tip of parieto-supraoccipital process and the anterior tip of nuchal plate.

As previously discussed, A. taurus is a synonym of A. albater and, in fact, the infraorbital 2 of some A. albater specimens can be entirely covered by a thick layer of skin, but this is not the case of infraorbital 1, which is partially exposed (see Remarks for A. albater ). However, Leão et al. (2015) did not consider any bone as exposed or not, but rather externally visible or not, referring to the thin outermost layer of skin that covers the entire body as “thick skin” (MRB, pers. obs.). This outermost layer becomes whitish/ opaque after preservation, making it difficult to observe some structures in integrous specimens, especially the infraorbital bones. In contrast, this layer of superficial skin is completely transparent in live specimens (LFCT, pers. obs.), and is completely lost after the clearing-and-staining process, as observed in Leão et al. (2015:582, fig. 3). Therefore, as the bones covered only by this outermost layer of skin are considered herein as exposed, the condition observed in the infraorbitals of A. marianae is shared with all congeners (except for some specimens of A. albater ). Additionally, the presence of platelets between parieto-supraoccipital process and nuchal plate are not only present in A. albater but also in A. fuscoguttatus , A. kiriri , A. lakoi , A. poecilus , and A. raimundi .

The analysis of specimens from the rio Curuá basin that are clearly compatible with A. marianae allowed us to confirm the presence of the following features: (I) small platelets on the snout (although sparser), (II) infraorbitals 1 and 2 almost entirely exposed, and (III) medium-sized to relatively large platelets between parieto-supraoccipital process and nuchal plate. Additionally, it was possible to observe the presence of infraorbital 1 with ventral and anterior laminar expansions generally extremely well developed, and with a moderately-developed inner laminar expansion; narrow frontal bone; parapophysis of complex vertebra moderately developed; dorsal fin with dark brown or black spots, variably longitudinally or obliquely aligned, with concentration of dark brown or black chromatophores on membranes, forming longitudinal or oblique bar in some specimens; anterior portion of dorsal fin variably with concentration of dark brown or black chromatophores; and markings on ventrolateral body plates relatively numerous and evident, not considering the number of blotches in the series along flank midline. Since the combination of these features is, basically, the diagnosis of A. poecilus , and no additional conspicuous diagnostic feature differing this population from the typical A. poecilus was observed, A. marianae is also placed under its synonymy.

Some populations from the rio Tocantins basin in Goiás and Tocantins states ( Fig. 56B ), and from the rio Tapajós basin in Mato Grosso State ( Fig. 56C ) also presented a similar variation pattern in osteological and coloration features to specimens from the rivers Araguaia and Culuene basins. For this reason, these populations are also attributed to A. poecilus . Nijssen, Isbrücker (1976) reported the presence of a possible new species similar to A. poecilus , which they called Aspidoras sp. aff. poecilus . Although it was not possible to reanalyse this material, that is basically from the rio Tocantins basin in Goiás State, several specimens from this region were examined, revealing the presence of A. albater and A. poecilus . Therefore, it is quite possible that the material listed by Nijssen, Isbrücker (1976:122) includes at least one of these species, which can only be confirmed through its re-examination.

Aspidoras poecilus is a relatively common species in the aquarium hobby. Additionally, two of the coded Aspidoras species likely represent A. poecilus , C37, said to be from the rio Araguaia basin in Goiás, and C158, said to be from the rio da Paz, a tributary to the rio Xingu in Pará. Although CW126, said to be from the rio Teles Pires basin, a tributary to the rio Tapajós basin, presents compatible locality and similar morphological pattern to A. poecilus , its color pattern slightly differs by having head densely covered by dark brown or black chromatophores, which gives it a “dirty” aspect. This minor difference in color pattern may not be enough to distinguish CW126 from A. poecilus but, since this difference was observed, it would be necessary to examine CW126 material before concluding that it represents a distinct morphotype of A. poecilus .

Material examined. In addition to the material examined by Nijssen, Isbrücker (1976: 121), the following material was analysed. All from Brazil. Rio Xingu basin. ANSP 187252, 10, 19.2‒26.0 mm SL, Mato Grosso, córrego Formoso. CPUFMT 2060, 5 of 6, 12.1‒27.7 mm SL, 1 CS of 6, 27.6 mm SL, Pará, unnamed stream tributary to the rio Curuá. CPUFMT 4305, 1, 22.8 mm SL, Pará, unnamed stream. CPUFMT 4306, 5, 16.4‒23.4 mm SL, Pará, unnamed stream. CPUFMT 4307, 5, 16.6‒28.2 mm SL, Pará, unnamed stream. LBP 15714, 34 of 35, 12.9‒25.2 mm SL, 1 CS of 35, 26.0 mm SL, Mato Grosso, unnamed stream tributary to the rio Suiazinho. LBP 15732, 3, 20.8‒29.6 mm SL, Mato Grosso, unnamed stream tributary to the ribeirão Manda Brasa. LBP 15850, 33, 17.5‒35.0 mm SL, Mato Grosso, unnamed stream tributary to the rio Suiá-Miçu. LBP 15860, 5 of 6, 14.1‒26.2 mm SL, 1 CS of 6, 26.2 mm SL, Mato Grosso, unnamed stream tributary to the ribeirão Tangurinho. LBP 15895, 31 of 32, 15.5‒30.2 mm SL, 1 CS of 32, 27.1 mm SL, Mato Grosso, unnamed stream tributary to the rio Tanguro. LIRP 3972, 1, 32.7 mm SL, Mato Grosso, unnamed stream tributary to the rio Culuene. MNRJ 33854, 1, 20.2 mm SL, Pará, córrego dos Maias. MNRJ 33855, 1, 19.1 mm SL, Mato Grosso, unnamed stream. MZUSP 62609, 4, 18.0‒ 19.8 mm SL, Mato Grosso, ribeirão Suiazinho. MZUSP 62611, 8, 8.1‒18.0 mm SL, Mato Grosso, córrego Piabanha. MZUSP 62612, 6, 9.9‒22.3 mm SL, Mato Grosso, córrego Piabanha. MZUSP 86836, 11, 14.6‒24.2 mm SL, Mato Grosso, rio Tanguro. MZUSP 86842, 74 of 75, 14.5‒27.0 mm SL, Mato Grosso, córrego Formoso. MZUSP 86856, 28 of 48, 9.5‒27.8 mm SL, Mato Grosso, stream tributary to the rio Suiá-Miçu. MZUSP 87152, 8 of 18, 18.4‒21.2 mm SL, Mato Grosso, rio Suiazinho. MZUSP 87153, 24, 14.7‒22.9 mm SL, Mato Grosso, córrego Capim. MZUSP 95587, 4, 18.9‒22.8 mm SL, Mato Grosso, rio Coronel Vanick. MZUSP 97074, 1, 24.3 mm SL, Mato Grosso, córrego Água Fria. MZUSP 97759, 1, 29.2 mm SL, Mato Grosso, rio Tanguro. MZUSP 97789, 1, 22.3 mm SL, Mato Grosso, unnamed stream crossing the road MT 110. MZUSP 97887, 1, 21.9 mm SL, Mato Grosso, córrego Tangará. MZUSP 98011, 13, 19.1‒28.8 mm SL, Mato Grosso, stream tributary to a marginal lagoon of the rio Couto de Magalhães. MZUSP 98064, 5 of 15, 22.2‒24.2 mm SL, Mato Grosso, córrego Água Limpa. MZUSP 98084, 2, 21.8‒27.0 mm SL, Mato Grosso, unnamed stream tributary to the rio Couto de Magalhães. MZUSP 116625, 17, 15.6‒28.6 mm SL, Pará, stream tributary to the rio Curuá. Rio Tapajós basin. MNRJ 23536, 1, 18.5 mm SL, Mato Grosso, rio Braço Dois. MNRJ 24624, 1, 18.6 mm SL, Mato Grosso, córrego Doce. MNRJ 24640, 2, 25.2‒28.0 mm SL, Mato Grosso, unnamed stream tributary to the rio Peixoto de Azevedo. MNRJ 33856, 2 of 22, 20.5‒22.9 mm SL, Mato Grosso, unnamed stream. MNRJ 33857, 2, 16.8‒19.4 mm SL, Mato Grosso, rio Cristalino. MNRJ 33858, 1, 23.3 mm SL, Mato Grosso, rio Cristalino. Rio Araguaia basin. CITL 389, 1, 28.8 mm SL, Mato Grosso, ribeirão Taquaral. CITL 390, 1, 22.7 mm SL, Mato Grosso, córrego Grande. LBP 4019, 18, 15.6‒28.4 mm SL, Mato Grosso, córrego Taquaralzinho. LBP 20797, 14, 18.0‒25.0 mm SL, Mato Grosso, córrego Taquaralzinho. NUP 19123, 4, 22.3‒29.0 mm SL, Mato Grosso, córrego Fogaça. Rio Tocantins basin. LBP 19126, 15, 14.7‒29.9 mm SL, Goiás, rio Uburixama. LIRP 11103, 6, 17.4‒25.2 mm SL, Tocantins, córrego Presídio. UNT 5531, 6, 15.4‒22.0 mm SL, Tocantins, rio Tocantins. UNT 5535, 6, 10.5‒28.8 mm SL, Tocantins, córrego Bufú. UNT 5548, 9 of 10, 16.4‒22.9 mm SL, 1 CS, 23.0 mm SL, Tocantins, córrego Fundo. UNT 6234, 29 of 51, 24.9‒38.8 mm SL, 1 CS of 51, 33.1 mm SL, Tocantins, córrego dos Vidros. UNT 6249, 29 of 46, 20.4‒32.8 mm SL, 1 CS of 46, 30.9 mm SL, Tocantins, ribeirão Manduca. UNT 11401, 6, 15.0‒ 18.7 mm SL, Tocantins, rio Areias. UNT 12056, 3 of 4, 18.8‒32.4 mm SL, 1 CS of 4, 31.5 mm SL, Tocantins, unnamed stream. UNT 12251, 2, 19.2‒21.2 mm SL, Tocantins, córrego Pontal and ribeirão Carmo.

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 50 | Aspidoras poecilus, holotype, IRSNB 560, 29.2 mm SL, creek upstream the Porori Village, left bank of the rio Xingu, Mato Grosso State, Brazil. Dorsal (top), lateral (middle) and ventral (bottom) views. Photos by Mark Allen.

FIGURE 51 | Lateral view of the head of CS specimens of Aspidoras poecilus, showing the infraorbitals patterns of the species. Ventral laminar expansion of infraorbital 1 moderately developed in (A) (LBP 15895, 27.1 mm SL), and strongly well developed in (B) and (C) (UNT 6249, 30.9 mm SL and CPUFMT 2060, 27.6 mm SL, respectively). Abbreviations: io1: infraorbital 1, io2: infraorbital 2, sph: sphenotic, pes: pterotic-extrascapular. Scale bars = 1 mm.

FIGURE 52 | Predorsal region of trunk in dorsal view in CS specimens of Aspidoras poecilus, showing the following morphological variation: nuchal plate (A) separated from the posterior process of the parieto-supraoccipital by the first dorsolateral body plate (UNT 6249, 30.9 mm SL), (B) separated from the posterior process of the parieto-supraoccipital by the first dorsolateral body plate, with platelets on the region between them, and (C) nearly contacting the posterior process of the parieto-supraoccipital. 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 bars = 1 mm.

FIGURE 53 | Dorsal view of pectoral fin in CS specimens of Aspidoras poecilus, showing variation in the morphology of pectoral-fin spine: (A) presence of simple and/or bifid moderately-developed serrations on its posterior margin (UNT 6249, 30.9 mm SL), or (B) with simple and/ or bifid moderately- and/or well-developed serrations on its posterior margin (LBP 15860, 26.2 mm SL). Arrows indicate the small laminar expansions at the base of branched rays. Scale bars = 1 mm.

FIGURE 54 | Aspidoras poecilus photographed alive, showing the general color pattern variations in (A) an uncatalogued aquarium specimen said to be from the rio Araguaia basin, (B) a specimen from a stream tributary to the rio Curuá, rio Xingu basin (MZUSP 116625, not measured), (C) an uncatalogued specimen from the rio Culuene basin, and (D) a specimen from the rio Uburixama, rio Tocantins basin (LBP 19126, not measured). Photos by Ingo Seidel (A), Willian Ohara (B), Cristiano Moreira (C), and Martin Taylor (D). Scale bar in (B) = 5 mm.

FIGURE 55 | Map showing the geographical distribution of Aspidoras poecilus (type locality: red circle; non-type localities: black circles), A. psammatides (type locality: purple cross; non-type localities: white crosses), A. raimundi (type locality: red triangle; non-type localities: white triangles), A. rochai (type locality: red star), and A. velites (type locality: purple diamond; non-type localities: white diamonds). Each symbol may represent more than one locality.

FIGURE 56 | Specimens of Aspidoras poecilus showing variations in general morphological and color patterns in lateral view; (A) CITL 390, 22.7 mm SL, rio Araguaia basin, (B) UNT 6234, 38.8 mm SL, rio Tocantins basin, and (C) MNRJ 24640, 25.2 mm SL, rio Tapajós basin.

FIGURE 57 | Holotype of Aspidoras microgalaeus, junior synonym of Aspidoras poecilus, MZUSP 51209, 25.7 mm SL, small tributary to the rio Culuene, km 86 of the Paranatinga – Canarana Road, Mato Grosso State, Brazil. Dorsal (top), lateral (middle) and ventral (bottom) views. Photo in lateral view by Eduardo Baena.