Aspidoras velites Britto

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 : 141-150

Aspidoras velites Britto , Lima & Moreira, 2002

( Fig. 74 )

Aspidoras velites Britto , Lima & Moreira, 2002:727‒736 (original description; type locality: córrego Boiadeiro , Mato Grosso State, Brazil). — Britto et al., 2005:477 (morphological comparison). — Ferraris , 2007:110 (listed). — Wosiacki et al., 2014:311 (morphological comparison). — Leão et al., 2015:578 (morphological comparison). — Tencatt, Bichuette, 2017:8 (morphological comparison).

Diagnosis. Aspidoras velites can be distinguished from all of its congeners by the presence of the following features: parieto-supraoccipital fontanel located close to origin of posterior process (vs. located medially or slightly displaced towards posterior portion of parieto-supraoccipital in A. albater ; slightly displaced towards anterior portion of parieto-supraoccipital in A. lakoi ; located medially on parieto-supraoccipital in remaining congeners), and ventral surface of trunk covered by striated platelets (vs. platelets, when present, non-striated). It can be further distinguished from its congeners, except for A. azaghal , by the absence of the first dorsal-fin element, the spinelet (vs. spinelet present); from A. azaghal plus A. albater , A. gabrieli , A. lakoi A. mephisto , A. psammatides , and A. rochai it differs by having a narrow frontal bone, with width 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 ). Aspidoras velites can be distinguished from its congeners, except for A. mephisto , by having conspicuously smaller preadipose azygous plates (vs. conspicuously larger); from A. mephisto by having well-developed pigmentation (vs. conspicuously reduced pigmentation). Additionally, A. velites can be distinguished from its congeners, except for A. albater , A. mephisto , and A. psammatides , by having anterior portion of infraorbital 1 with strongly reduced expansion, not reaching or at same level as posterior margin of nasal capsule (vs. moderately developed, reaching middle of nasal capsule in A. azaghal ; extremely well developed, reaching or surpassing anterior margin of nasal capsule in A. belenos ; well developed, surpassing middle of nasal capsule in A. depinnai and A. maculosus ; ranging from well developed, surpassing middle of nasal capsule, to extremely well developed, reaching anterior margin of nasal capsule in A. fuscoguttatus ; ranging from poorly developed, slightly surpassing posterior margin of nasal capsule, to moderately developed, reaching middle of nasal capsule in A. aldebaran and A. lakoi ; ranging from poorly developed, slightly surpassing posterior margin of nasal capsule, to extremely well developed, reaching anterior margin of nasal capsule in A. poecilus ; ranging from moderately developed, reaching middle of nasal capsule, to extremely well developed, reaching anterior margin of nasal capsule in A. raimundi ; at least well developed, surpassing middle of nasal capsule in A. rochai ).

Description. Morphometric data in Britto et al. (2002). Head slightly compressed with convex dorsal profile; somewhat trapezoid in dorsal view. Snout large and conspicuously pointed. Head profile convex from tip of snout to anterior nares; ascending nearly straight from this point to tip of posterior process of parieto-supraoccipital. Region between the tip of posterior process of parieto-supraoccipital and nuchal plate nearly straight; smoothly concave in some specimens. Profile nearly straight along dorsal-fin base; or smoothly convex. Postdorsal-fin body profile nearly straight to adipose-fin spine; smoothly 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; smoothly concave until caudal-fin base. Body acutely elliptical in cross section at pectoral girdle, smoothly 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 relatively distant to each other, separated by distance equal to twice of naris diameter. Anterior naris tubular. Posterior naris relatively distant to anterodorsal margin of orbit, separated from it by distance equal to twice of naris diameter. Mouth small, subterminal, width slightly larger than bony orbit diameter. Maxillary barbel moderate in size, not reaching 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 well developed, forming relatively large triangular fleshy flap. Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout and isthmus.

Mesethmoid short; anterior tip well developed, larger than 50% of bone length (see Britto, 2003:123, ch. 1, state 0; fig. 1A); posterior portion wide, partially exposed. Nasal slender, smoothly curved laterally, inner margin with moderately-developed laminar expansion; outer margin with reduced laminar expansion; mesial border contacting frontal and mesethmoid.

Frontal elongated, narrow, with width smaller than half of entire length ( Fig. 3A ); anterior projection short, size smaller than nasal length. 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 moderate in size, posterior process strongly reduced, not contacting nuchal plate. Parieto-supraoccipital medial keel expanded ventrally; laminar, with posterior portion expanded posteriorly, surpassing tip of posterior process. Parieto-supraoccipital fontanel small, ellipsoid; located close to origin of posterior process.

Two laminar infraorbitals with minute odontodes; infraorbital 1 large, ventral laminar expansion extremely reduced; anterior portion with strongly reduced laminar expansion, not reaching or at same level as posterior margin of nasal capsule ( Fig. 75 ); inner laminar expansion poorly developed ( Fig. 5D ); small portions of external surface covered by thick layer of skin; infraorbital 2 small, slender; with posterior laminar expansion strongly reduced; posteroventral margin not in contact with posterodorsal ridge of hyomandibula, dorsal tip contacting only sphenotic; small portions of external surface covered by thick layer of skin ( Fig. 75 ). Posterodorsal ridge of hyomandibula, close to its articulation with opercle, oblong, slender; exposed, generally bearing small odontodes; dorsal ridge of hyomandibula, between pterotic-extrascapular and opercle, typically covered by thick layer of skin. Interopercle generally entirely covered by thick layer of skin; somewhat triangular, anterior projection well developed. Preopercle slender, elongated, minute odontodes sparse on external surface. Opercle slightly more elongated dorso-ventrally, width nearly equal to half of its length; free margin smoothly 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 moderately developed, size similar to cartilaginous portion; or poorly developed, size smaller than cartilaginous portion. Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with small process on anterior margin of mesial portion; ceratobranchial 3 with continuous postero-lateral margin; variably notched; ceratobranchial 5 toothed on postero-dorsal surface, 16 to 19(3) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, variably with small pointed process on laminar expansion of posterior margin; epibranchial 3 with triangular uncinate process on laminar expansion of posterior margin. Two pharyngobranchials (3 and 4); pharyngobranchial 3 wide, with triangular laminar expansion on posterior margin; expansion with notch in some specimens; pharyngobranchial 4 reduced. Upper tooth plate oval, with 19 to 27(3) 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; 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. Nasal canal with two to three openings, first on posterior edge, second, if present, on posterolateral portion, generally fused with first pore, and third on anterior edge. Infraorbital canal running through entire second infraorbital, extending to infraorbital 1 and opening into two pores. Preoperculomandibular branch giving rise to preoperculo-mandibular canal, which generally runs through posterodorsal ridge of hyomandibula and entire preopercle with three openings, leading to pores 3, 4, and 5, respectively; pore 3 opening at posterodorsal ridge of hyomandibula.

Dorsal fin somewhat triangular, located just posterior to third or fourth dorsolateral body plate. Dorsal-fin rays I,8*(59), posterior margin of dorsal-fin spine smooth. Nuchal plate poorly developed in length; strongly reduced in some specimens; covered by thick layer of skin ( Fig. 76 ); spinelet absent ( Fig. 76A ); single specimen (MZUSP 73264, 20.5 mm SL, paratype) with strongly reduced and irregular bony plate added to dorsal-fin spine basis, possibly reminiscent of first dorsal-fin element ( Fig. 76B ); spine poorly developed, adpressed distal tip slightly surpassing middle portion of dorsal-fin base; anterior margin with small odontodes. Pectoral fin oblong, its origin just posterior to gill opening. Pectoral-fin rays I,7(29), I,8*(29), I,9(4); posterior margin of pectoral spine with two to six extremely reduced serrations; serrations generally perpendicularly directed; some serrations slightly directed towards tip or origin of spine 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. 77 ); Anteroventral portion of cleithrum partially exposed; posterolateral portion of scapulocoracoid reduced, externally visible. Pelvic fin oblong, located just below fourth ventrolateral body plate, and at vertical through second dorsal-fin branched ray. Pelvic-fin rays i,5. Adipose fin roughly triangular, separated from posterior origin of dorsal-fin base by generally eight 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. Anal-fin rays ii,6*(54), ii,7(8). Caudal-fin rays i,12,i(22), generally four dorsal and/or ventral procurrent rays; caudal fin bilobed, lobes with similar size.

Three or 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 well-developed odontodes confined to posterior margins; dorsolateral body plates 25(2), 26(16), 27*(33), 28(11); ventrolateral body plates 24*(21), 25(19), 26(9); dorsolateral body plates along dorsal-fin base 4(10), 5*(47), 6(5); dorsolateral body plates between adipose-fin spine and caudal-fin base 8(9), 9*(43), 10(10); preadipose platelets 1(2), 2(11), 3(8), 4(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. Ventral surface of trunk covered by striated platelets; posterior portion of isthmus generally with platelets (see Tencatt, Bichuette, 2017:8, fig. 6b).

Vertebral count 25(3); ribs 5(2), 6(1) 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. Snout covered by dark brown or black chromatophores on its dorsal surface; chromatophores generally more concentrated on region of nasal bone and posterior portion of mesethmoid; with conspicuous dark brown or black stripe from anteroventral portion of orbit to upper lip lateral area. Upper lip and maxillary barbel with dark brown or black chromatophores; outer mental barbel covered by dark brown or black chromatophores, generally more concentrated on its proximal portion. 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, middle portion of caudal peduncle, and fifth, if present, on caudal-fin base; blotches variably diffuse. Dorsal portion of body with 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 lacking dark brown or black chromatophores; region posterior to urogenital opening with dark brown or black chromatophores in some specimens. First dorsolateral body plate almost entirely covered by dark brown or black chromatophores; posterior margin of some dorso- and ventrolateral plates, and region of lateral line canals with conspicuous concentration of dark brown or black chromatophores in some specimens. Midline of flank with relatively wide longitudinal dark brown or black stripe. Dorsal portion of dorsolateral body plates with conspicuous concentration of dark brown or black chromatophores; region of anterior and posterior portions of dorsal-fin base and adipose-fin base with slightly more concentrated chromatophores in some specimens. Ventral half of dorsolateral body plates and dorsal half of ventrolateral body plates with concentration of dark brown or black chromatophores, generally more evident on anterior portion of body, in some specimens. Ventral portion of ventrolateral body plates with concentration of dark brown or black chromatophores, generally more evident from region posterior to pelvic-fin origin to region just posterior to anal-fin posterior origin, forming longitudinal slender black stripe; stripe variably diffuse or fragmented. Dorsal fin with dark brown or black chromatophores, generally restricted to rays; chromatophores generally more concentrated on proximal half of rays; 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, generally more evident on its distal portion. Pectoral fin with dark brown or black chromatophores on its dorsal surface, generally more evident on spine and first branched rays; or almost entirely hyaline; region of body around dorsal portion of pectoral-fin origin with concentration of dark brown or black chromatophores in some specimens. Pelvic generally covered by dark brown or black chromatophores on its dorsal surface; almost entirely hyaline in some specimens; chromatophores generally restricted to rays; region of body around dorsal portion of pelvic-fin origin variably with concentration of dark brown or black chromatophores. Adipose-fin membrane with dark brown or black chromatophores, generally more evident close to spine; almost entirely hyaline in some specimens; adipose-fin spine generally with dark brown or black chromatophores. Anal with dark brown or black chromatophores, generally restricted to rays; chromatophores more concentrated on proximal half of branched rays; variably with one or two dark brown or black diffuse blotches. Middle portion of caudal-fin base, just posterior to flank midline stripe, generally with medium-sized dark brown or black blotch that is fused with stripe; diffuse in some specimens. Caudal fin with dark brown or black chromatophores, generally more evident on rays; forming one to four transversal dark brown or black relatively wide bars in some specimens.

Coloration in life. Freshly collected specimens present ventral portion of body beige, dorsal portion of body yellowish orange, and midline longitudinal stripe orangebrown. Specimens settled in biotope aquarium displayed a similar color pattern to that observed in preserved specimens but with ground color of body grayish yellow. Body covered by whitish yellow and green iridescent coloration ( Fig. 78A ). See Britto et al. (2002:732) for further information on coloration in life.

Geographical distribution. Aspidoras velites is known only from the upper portion of the rio Araguaia basin, in the regions of Alto Araguaia Municipality, Mato Grosso State, and of Santa Rita do Araguaia Municipality, Goiás State, Brazil ( Fig. 55 ) .

Ecological notes. At the córrego Gordura, Aspidoras velites was typically found in shallow stretches (up to 20 cm), with moderate current, substrate composed mainly by sand and gravel, and associated with marginal and/or submerged vegetation ( Fig. 78B ). General physical aspects of the córrego Gordura as well as the behaviour of A. velites in aquarium were provided herein in the “Ecological notes” section for Aspidoras aldebaran . Further habitat and ecological notes were provided by Britto et al. (2002:732–733).

Conservation status. The Extent of Occurrence of A. velites was estimated to be restricted to 70 km 2. Despite the considerably large type series, recent survey efforts led by LFCT (2018) to the Alto Araguaia/Santa Rita do Araguaia region suggest that this species possibly suffered a populational reduction, being captured in clearly smaller numbers when compared to the material listed in the original description (captured in 2001). This conspicuous reduction may be related to the impacts caused by anthropic activities in the region (see A. aldebaran Conservation status section) and the fragility of the headwater streams in which this species mostly occurs. Besides the region being relatively well sampled, the recent survey efforts by LFCT plus the extensive material raised during this review did not significantly alter the previously known geographical distribution of A. velites , which suggests it as a narrowly endemic species. According to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019), Aspidoras velites can be classified, at least, as Near Threatened (NT), approximating the Critically Endangered (CR) category by criterion B1b(iii).

Remarks. Aspidoras velites presents some peculiar and apparently exclusive features, besides its general morphological pattern, which makes it the most peculiar species within Corydoradinae . One of the possible exclusive features is the presence of clearly larger and striated platelets on ventral surface of the trunk (see Tencatt, Bichuette, 2017:8, fig. 6b), whereas remaining species present clearly smaller and roundish or irregular platelets (see Tencatt, Bichuette, 2017:8, fig. 6a). Additionally, A. velites presents dorsal- and pectoral-fin spines with extremely reduced ossified portion, which is also potentially exclusive to it. Contrary to Britto et al. (2002:731), the presence of spine in pectoral fin was considered herein for all specimens, though strongly reduced, because of the coossification of its proximal segments, typically showing very small serrations ( Fig. 77 ).

In the original description, the authors also mentioned the presence of another unique feature, a reduced and narrow posterior process of the parieto-supraoccipital (see Britto et al., 2002:733), which was confirmed herein. The length of the process itself is not so different from what is observed in some species, like A. mephisto (see Tencatt, Bichuette, 2017:7, fig. 4). However, a narrow parieto-supraoccipital posterior process was only observed in A. velites . Although Britto et al. (2002:733) presented the widely-spaced counterparts of the dorsolateral plates on predorsal region of body as an exclusive feature for A. velites , the later discovery and subsequent description of A. gabrieli reported a similar condition (Wosiacki et al., 2014:315) for that species.

As pointed out by Tencatt, Bichuette (2017:8), A. velites lacks a dorsal-fin spinelet ( Fig. 76A ), though a single specimen presented a small platelet-like bony structure adhered to dorsal-fin spine base ( Fig. 76B ). Among the Callichthyidae , the only species sharing this feature so far are A. azaghal (Tencatt et al., 2020:4, fig. 3) and Callichthys callichthys . Considering the clear differences between these species, it seems reasonable to conclude that this character may have developed independently in these taxa. These authors also mentioned the unusual position of the parieto-supraoccipital fontanel, which is located close to origin of posterior process (see Tencatt, Bichuette, 2017:7, fig. 4b; Fig. 76B ). In other Callichthyidae with parieto-supraoccipital fontanel, this structure is generally located medially on bone, with exception of A. lakoi , in which it is slightly displaced towards anterior portion of the bone, and some specimens of A. albater , which presents it slightly displaced towards posterior portion of the bone.

Material examined. In addition to the material examined by Britto et al. (2002:728‒729), the following material was analysed. all from Brazil, upper rio Araguaia basin. CITL 391, 3, 22.0– 26.1 mm SL, Mato Grosso, córrego Gordura. LIRP 4435, 14 of 16, 19.6‒26.6 mm SL, 2 CS of 16, 22.7‒23.4 mm SL, Mato Grosso, ribeirão do Sapo. LIRP 4446, 8, 16.9‒21.9 mm SL, Goiás, rio Araguaia. LIRP 4479, 11 of 12, 18.6‒29.0 mm SL, 1 CS of 12, 22.0 mm SL, Goiás, rio Araguaia. LIRP 4492, 5, 19.7‒22.2 mm SL, Mato Grosso, ribeirão do Sapo.

Identification key to the species of Aspidoras

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 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 74 | Aspidoras velites, holotype, MZUSP 74447, 23.6 mm SL, córrego Boiadeiro, Mato Grosso State, Brazil. Dorsal (top), lateral (middle) and ventral (bottom) views. Photos by Willian Ohara.

FIGURE 75 | Lateral view of the head of CS paratype of Aspidoras velites, MZUSP 73264, 20.6 mm SL, showing its general infraorbitals pattern. Abbreviations: io1: infraorbital 1, io2: infraorbital 2, sph: sphenotic, pes: pteroticextrascapular. Scale bar = 1 mm.

FIGURE 76 | Predorsal region of trunk in dorsal view in CS specimens of Aspidoras velites, showing the following morphological variation: (A) absence of dorsal-fin spinelet and bony platelet (LIRP 4435, 23.4 mm SL), and (B) absence of nuchal plate but presenting a reduced and irregular bony platelet on anterior margin of dorsal-fin spine base (black arrow) (MZUSP 73264, paratype, 20.6 mm SL). Dotted lines in (B) 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, dfs: dorsal-fin spine, pso: parieto-supraoccipital. Scale bars = 1 mm.

FIGURE 77 | Aspidoras velites, LIRP 4479, CS, 22.0 mm SL, showing dorsal view of the pectoral fin. Arrows indicate the small laminar expansions at the base of branched rays. Scale bar = 1 mm.

FIGURE 78 | Uncatalogued specimen of Aspidoras velites photographed alive (A), showing its typical habitat at the córrego Gordura, rio Araguaia basin (B). Photos by Hans Evers.