Aspidoras belenos Britto, 1998

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 : 40-49

Aspidoras belenos Britto, 1998

( Fig. 20 )

Aspidoras belenos Britto, 1998:361 (original description; type locality: creek at Primavera do Leste – Paranatinga road, 82 km north from Primavera do Leste, Mato Grosso State, Brazil). — Britto, 2000:1054 (listed as comparative material). — Lima, Britto, 2001:1015 (listed as comparative material). — Britto, 2003:144 (phylogeny). —Reis, 2003:292 (listed). —Ferraris, 2007:108 (listed). —Wosiacki et al., 2014:315 (listed as comparative material). —Leão et al., 2015:578 (morphological comparision). —Oliveira et al., 2017:e160118[7] (listed as comparative material with wrong catalog number, MNRJ 12933 instead of MNRJ 12433). —Tencatt, Bichuette, 2017:8 (morphological comparison).

Diagnosis. Aspidoras belenos can be distinguished from its congeners, with exception of A. aldebaran , A. kiriri , and A. raimundi , by having parapophysis of the complex vertebra well developed (vs. moderately developed in A. depinnai , A. lakoi , A. maculosus , A. mephisto , A. poecilus , A. psammatides , and A. velites ; poorly to moderately developed in A. albater and A. fuscoguttatus ; poorly developed in A. azaghal ); it differs from A. kiriri by the absence of a large and intensely pigmented black blotch on dorsal fin (vs. presence); from A. aldebaran by having anterior portion of infraorbital 1 with extremely well-developed laminar expansion, reaching or surpassing anterior margin of nasal capsule (vs. ranging from poorly developed, slightly surpassing posterior margin of nasal capsule, to moderately developed, reaching middle of nasal capsule); it can be distinguished from A. raimundi by having the following combination of features: absence of large and intensely pigmented dark brown or black blotch on dorsal fin (vs. blotch generally present), and markings on ventrolateral body plates generally present and clearly more numerous, not considering the number of blotches in the series along flank midline (vs. markings, when present, clearly scarcer). It can be further distinguished from A. albater , A. azaghal , A. gabrieli , A. lakoi , A. mephisto , 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 ).

Description. Head compressed with convex dorsal profile; triangular or somewhat trapezoid in dorsal view. Snout moderately developed and pointed. Head profile convex from tip of snout to anterior nares; ascending slightly convex from this point to dorsal-fin origin; region of parieto-supraoccipital process slightly concave in some specimens. Profile slightly convex along dorsal-fin base. Postdorsal-fin body profile slightly concave to adipose-fin spine; slightly concave from this point to caudal-fin base. Ventral profile of body 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 equal to or slightly smaller than naris diameter. Mouth small, subterminal, width 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 moderately developed, forming one triangular or semicircular fleshy flap, forming structure similar to barbel in some specimens. Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout and isthmus.

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

Frontal elongated, narrow, with width slightly 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, compound pterotic 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 moderately developed, close but not directly contacting nuchal plate; directly in contact in some specimens. Parieto-supraoccipital medial keel expanded ventrally; laminar, with posterior portion generally expanded posteriorly, slightly surpassing tip of posterior process. Parieto-supraoccipital fontanel small, roundish; located medially on parieto-supraoccipital.

Two laminar infraorbitals with minute odontodes; infraorbital 1 large, ventral laminar expansion from well to extremely well developed; anterior portion generally with extremely well-developed laminar expansion, reaching or surpassing anterior margin of nasal capsule ( Fig. 21 ); inner laminar expansion generally moderately developed ( Fig. 5C ); small portions of external surface covered by thick layer of skin; infraorbital 2 small, slender; with posterior laminar expansion poorly developed; inner laminar expansion moderately developed; posteroventral margin contacting posterodorsal ridge of hyomandibula, dorsal tip contacting only sphenotic; small portions of external surface covered by thick layer of skin ( Fig. 21 ). Posterodorsal ridge of hyomandibula, close to its articulation with opercle, oblong, relatively slender; exposed; dorsal ridge of hyomandibula, between pterotic-extrascapular and opercle, exposed; exposed areas generally bearing small odontodes. Interopercle covered by thick layer of skin on its anterior portion; somewhat triangular, anterior projection moderately developed. Preopercle relatively slender, elongated, minute odontodes sparse on external surface. Opercle more elongated dorso-ventrally, width equal to or slightly larger than half of its length; free margin convex; posterodorsal region with smoothly concave area in some specimens; 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, about same size of 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; ceratobranchial 5 toothed on postero-dorsal surface, 19 to 22 (2) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, lacking 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 with rounded notch in some specimens. Upper tooth plate oval, with 24 to 28 (2) 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. Nasal canal with three openings, first on posterior edge, second on posterolateral portion, generally fused with the first pore, and third on anterior edge. Infraorbital canal running through entire second infraorbital, extending to infraorbital 1 and generally opening into two pores. Preoperculomandibular branch giving rise to preoperculo-mandibular canal, which runs through entire preopercle with three openings, leading to pores 3, 4, and 5, respectively; pore 3 opening at posterodorsal ridge of hyomandibula in some specimens.

Dorsal fin somewhat triangular, located just posterior to second or third dorsolateral body plate. Dorsal-fin rays II,7,i*(2), II,8(1); posterior margin of dorsal-fin spine smooth. Nuchal plate moderately developed in length; almost entirely exposed; anterior tip covered by thick layer of skin ( Fig. 22 ); spinelet short, partially exposed; spine relatively well developed, adpressed distal tip reaching or 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*(3); posterior margin of pectoral spine with 14 to 23 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; bifid serrations generally present; base of branched rays with small laminar expansions on inner margin, generally more evident on first rays; laminar expansions with irregular margins in some specimens ( Fig. 23 ). Anteroventral portion of cleithrum partially exposed; posterolateral portion of scapulocoracoid reduced, externally visible. Pelvic fin oblong, located just below third ventrolateral body plate, and at vertical through second dorsal-fin branched ray. Pelvic-fin rays I,5*(3). Adipose fin somewhat triangular, separated from posterior origin of dorsal-fin base by seven or eight dorsolateral body plates. Anal fin somewhat triangular, located just posterior to 12 th or 13 th ventrolateral body plates, and at vertical through adipose-fin spine origin or region of preadipose platelets. Anal-fin rays, ii,5(1), ii,5,i*(2). Caudal-fin rays i,12,i*(3), generally four or five dorsal and/or ventral procurrent rays; caudal fin bilobed, dorsal and ventral lobes with similar size; dorsal lobe slightly larger or smaller than ventral lobe in some specimens.

Three 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, fifth dorsolateral body plates, respectively; sixth plate on left side of body with isolated pore in one paratype (UFRJ 1206, 21.4 mm SL). Body plates with conspicuous line of relatively large odontodes confined to posterior margins; dorsolateral body plates 23(1), 25*(2); ventrolateral body plates 21(1), 22*(2); dorsolateral body plates along dorsal-fin base 5*(3); dorsolateral body plates between adipose-fin spine and caudal-fin base 7(1), 9*(2); preadipose platelets 2(1), 3*(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 junction of frontal and lateral ethmoid, with small platelets. Ventrolateral portion of snout with relatively large platelets in some specimens. Ventral surface of trunk with small irregular platelets.

Vertebral count 23(2); ribs 5(1), 6(1), first pair conspicuously large; parapophysis of complex vertebra well developed ( Fig. 8A ).

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 with dark brown or black chromatophores on its dorsal surface, generally forming dark brown or black rounded, irregular or striated and relatively large spots in some specimens; generally, with dark brown or black diffuse or conspicuous stripe from anteroventral portion of orbit to upper lip lateral area. 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. Dorsal series of four to six dark brown or black blotches, first on anterior portion of dorsal-fin base, second on posterior portion of dorsal-fin base, third, if present, between dorsal and adipose fins, fourth on adipose-fin base, fifth, if present, on middle portion of caudal peduncle, and sixth 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. First dorsolateral body plate with conspicuous concentration of dark brown or black chromatophores; posterior margin of some dorsolateral 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 five medium-sized conspicuous dark brown or black blotches; blotches rounded, oblong or irregular. Dorsal half of dorsolateral body plates with dark brown or black chromatophores; region of anterior and posterior portions of dorsal-fin base and adipose-fin base 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, forming conspicuous blotches in some specimens; 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 spots; aligned spots, forming oblique bars in some specimens; membranes with dark brown or black chromatophores, generally more evident on region of first and second branched rays proximal portion; 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; chromatophores more evident on spine and first branched rays in some specimens; covered by dark brown or black spots in some specimens; spots generally diffuse and more evident on first branched rays. Pelvic fin generally with sparse dark brown or black chromatophores on its dorsal surface; almost entirely hyaline in some specimens. Adipose-fin membrane with dark brown or black chromatophores, generally more concentrated on its posterior portion; 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; generally, forming one dark brown or black blotch. 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 four transversal dark brown or black slender 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 iridescent coloration ( Fig. 24A ).

Geographical distribution. Aspidoras belenos is known only from the rio Suspiro basin, its type locality, a tributary to the rio das Mortes, Mato Grosso State, Brazil ( Fig. 10 ) .

Ecological notes. The type locality of A. belenos , a small stream tributary to the rio

Suspiro, rio das Mortes basin, presents width ranging from less than one meter to about five meters, and depth ranging from about 10 cm to nearly two meters ( Fig. 24B ). The species was found in shallow stretches (up to about 20 cm) with moderate current and substrate composed by sand, fine gravel, and larger rocks, where the specimens were observed burying themselves on sandy substrate through undulatory movements of the body. Aspidoras belenos seems to form small shoals of less than 10 individuals and was often found in syntopy with an unidentified species of Characidium .

Conservation status. Aspidoras belenos is currently known only from its type locality, a small stream tributary to the rio Suspiro, rio das Mortes basin, Mato Grosso. A new attempt to capture additional material of this species was made in 2017. The collecting trip led by LFCT to the type locality and the rio Suspiro itself resulted in the capture of additional specimens only at the type locality, where it seems to occur in low abundance. Considering the apparent rarity of the species and the fact that the region is still poorly known and presents severe evidence of anthropic impact, especially for agricultural purposes, it is not possible to adequately assess the risk of extinction of the population. According to the International Union for Conservation of Nature ( IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2019), Aspidoras belenos can be classified as Data Deficient (DD) .

Material examined. In addition to the material examined by Britto (1998:361), the following material was examined. All from Brazil, Mato Grosso, rio das Mortes basin, rio Araguaia basin. MZUSP 97703 , 1 , 22.3 mm SL, stream tributary to the rio Suspiro. CITL 388 , 4 , 21.8 –28.0 mm SL, same locality as holotype .

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 20 | Aspidoras belenos, holotype, MNRJ 12433, 27.3 mm SL, stream at the Primavera do Leste – Paranatinga Road, 82 km north from Primavera do Leste, Mato Grosso State, Brazil. Dorsal (top), lateral (middle) and ventral (bottom) views. Photos by Victor de Brito.

FIGURE 21 | Lateral view of the head of CS paratype of Aspidoras belenos, UFRJ 4419 (ex-UFRJ 3861), 22.1 mm SL, showing its general infraorbitals pattern. Abbreviations: io1: infraorbital 1, io2: infraorbital 2, sph: sphenotic, pes: pterotic-extrascapular. Scale bar = 1 mm.

FIGURE 22 | Aspidoras belenos, UFRJ 1206, paratype, 21.4 mm SL, showing predorsal region of trunk in dorsal view. Abbreviations: np: nuchal plate, pso: parieto-supraoccipital. Scale bar = 1 mm.

FIGURE 23 | Aspidoras belenos, UFRJ 4419 (ex-UFRJ 3861), CS paratype, 22.1 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 24 | Uncatalogued topotype of Aspidoras belenos photographed alive (A), and its typical habitat at the type locality, a stream with unknown name tributary to the rio Suspiro, rio das Mortes basin (B). Photos by Hans Evers.