Neotropical Ichthyology

A new species of Jupiaba Zanata is described from tributaries of the rio Aripuanã, rio Madeira basin, Amazonas and Mato Grosso States, Brazil. The new species can be diagnosed from its congeners (except J. abramoides, J. anteroides, and J. poranga) by having two vertically-elongated humeral blotches, the anterior usually with a darker median portion forming an horizontally-elongated trace pointed anteriorly, and a well defined dark longitudinal line extending from the second humeral blotch to the caudal peduncle. The new species differs from J. abramoides, J. anteroides, and J. poranga by having an elongated blotch over caudal peduncle that extends to the distal tip of the caudal-fin median rays. Also, it can be distinguished from most congeners by the combination of relatively high number of lateral line scales, predorsal median line without a series of scales, dentary teeth decreasing abruptly in size towards posterior portion, and presence of a larger central teeth cusp.Porto Alegr

Astyanax epiagos Zanata & Camelier, 2008, new species

Astyanax epiagos, new species Fig. 1 Holotype. MZUSP 89568 (59.3 mm SL), Brazil, Bahia, Morro do Chapéu, rio Ferro Doido, above Cachoeira do Ferro Doido, tributary of rio Jacuípe, Paraguaçu drainage, 11 ° 37 ’34.0’’N, 41 °00’ 11.5 ’’W, 899 m alt.; Zanata et al., 10 June 2005. Paratypes. All from Brazil, Bahia, Morro do Chapéu. UFBA 0 2792 (344, 3 c&s, 14.0– 52.6 mm SL). MZUSP 89569 (20, 23.7–42.6 mm SL). ANSP 189081 (20, 25.6–42.5 mm SL); collected with holotype. UFBA 0 2794 (6, 26.9–36.6 mm SL), tributary of rio Jacuípe 4 km from Morro do Chapéu, 41 °07’ 13.’’N, 11 ° 34 ’ 20.7 ’’W, 934 m alt.; Zanata et al., 10 June 2005. Diagnosis. Astyanax epiagos can be distinguished from most of its congeners and from all other Astyanax species known from northeastern Brazilian drainages (A. brevirhinus, A. fasciatus, A. intermedius, A. lacustris, A. pelecus, A. rivularis, and A. taeniatus) by a vertically elongated humeral blotch and body highest along vertical through midlength of pectoral fin (vs. distinctly horizontally elongated humeral spot and highest body depth just anterior to dorsal-fin origin in A. lacustris and A. pelecus), absence of dark stripe from humeral region to caudal peduncle (vs. well defined dark midlateral stripe along most of body length in A. intermedius, A. pelecus, A rivularis, A. taeniatus), 2–4 outer premaxillary teeth and total anal fin rays 17–21 (vs. 5 teeth and 28 anal-fin rays in A. brevirhinus). Astyanax epiagos can be further distinguished from A. rivularis by having lower number of perforated scales (35–36, rarely 34 or 37, vs. 39 scales), lower number of branched anal-fin rays (13–17 vs. 19), lower number of maxillary teeth (0–2 vs. 3–4), and shorter upper jaw length (31.6–41.4 % vs. 45.1–47.7 %). It can be also distinguished from A. intermedius by its slender body, with longer distance between posterior margin of eye and dorsal-fin origin (39.5–43.2 % vs. 33.7–38.2 %), longer distance from dorsal-fin origin to caudal-fin base (45.7–52.7 % vs. 53.0– 54.2 %), and narrower humeral blotch. The new species differs further from A. taeniatus by its lower number of branched anal-fin rays (13–17 vs. 19–24) and lower number of cusps on teeth (usually three to five vs. usually seven cusps, even on maxillary teeth) and from A. pelecus by its lower number of lateral line scales (35–36, rarely 34 or 37, vs. 38–39 scales) and longer caudal peduncle length (13.3–16.6 % vs. 11.3–13.2 %). It can be further distinguished from A. fasciatus by the absence of scales covering anal-fin rays base and body highest on vertical around midlength of pectoral fin (vs. presence of sheath of anal-fin scales and highest body depth just anterior to dorsal-fin origin). Astyanax epiagos can be distinguished from A. turmalinensis by its relatively smaller eye diameter (26.2– 34.1 % vs. 31.1–39.7 %), absence of scales covering base of anal fin-rays (vs. presence), slender body, narrower humeral blotch, wider naked area between ventral margin of infraorbitals and preopercle and narrower and more conspicuous black blotch on caudal peduncle. The new species is also distinguished from A. jacobinae by the presence of conspicuous dark blotch over caudal peduncle, extending through median caudal-fin rays, smaller eye diameter (26.2–34.1 % vs. 36.8– 40.3 %), shorter anal-fin base length (18.1–23.2 % vs. 27.6–30.7 %), relatively longer caudal peduncle length (13.9–18.6 % vs. 12.2 –14.0%), longer distance from eye to dorsal-fin origin (39.5–43.2 % vs. 36.0– 39.2 %), and by having infraorbitals comparatively less developed, leaving broad space between these ossifications and preopercle (see under ‘Discussion’ for diagnosis of the species from “ A. scabripinnis species complex”). Description. Morphometric data of the holotype and paratypes are presented in Table 1. Body somewhat compressed, robust, and elongate. Greatest body depth located around vertical through midlength of pectoral fin. Dorsal profile of head convex from upper lip to vertical through anterior nostrils; straight to slightly concave from latter point to tip of supraoccipital spine and nearly straight to slightly convex from this point to dorsal-fin origin; profile of predorsal portion of body slightly convex in all its extension in specimens around 28.0 mm SL. Body profile straight to somewhat convex along dorsal-fin base; straight from dorsal-fin base terminus to adipose fin; slightly concave between latter point to origin of dorsalmost procurrent caudal-fin ray. Ventral profile of head and body convex from tip of lower lip to anal-fin origin. Body profile along analfin base straight and posterodorsally inclined. Ventral profile of caudal peduncle nearly straight to slightly concave. Head obtusely rounded anteriorly in lateral profile; mouth terminal. Posterior terminus of maxilla extending slightly beyond anterior margin of orbit. Premaxillary and dentary teeth massive, cusps distributed in a gently arch facing oral cavity. Premaxillary teeth in two rows. Outer row with 2 (6), 3 * (20), or 4 (4) teeth bearing 3 or 5 cusps. Inner row with 4 (16) or 5 * (3) teeth bearing 4 to 7 cusps. Symphyseal tooth of inner series narrow, asymmetrical, with one cusp on anteromedial side, one larger central cusp and two smaller on lateral side, second teeth the larger, with 7 cusps, penultimate and last teeth with 4 cusps in two specimens and last teeth with 3 cusps in the other c&s specimen. Maxilla with 0 (2), 1 (21), or 2 * (6) teeth bearing 3 cusps. Dentary with 8 (3) somewhat elongate and symmetrical teeth, anterior ones similar in size, with 5 cusps, antipenultimate with 3 cusps and two posteriormost abruptly smaller teeth with 1 cusp. A. epiagos A. jacobinae Scales cycloid, circuli absent on exposed area of scales, with few slightly divergent radii extending to posterior margin of scales. Lateral line slightly decurved anteriorly, completely pored from supracleithrum to base of caudal fin, with 34 (1), 35 (9), 36 * (17), or 37 (1) perforated scales. Horizontal scale rows between dorsal-fin origin and lateral line 5 * (6) or 6 (23), not including scale of predorsal series situated just anterior to first dorsal-fin ray. Horizontal scale rows between lateral line and pelvic-fin insertion 4 * (18) or 5 (12). Scales along middorsal line between tip of supraoccipital process and origin of dorsal fin 10 (1), 11 (6), 12 * (14), or 13 (5). Horizontal scale rows around caudal peduncle 13 (3) or 14 * (22). Base of anteriormost anal-fin rays not covered by series of scales. Dorsal-fin rays ii, 9 (30). Distal margin of dorsal fin straight or slightly rounded. Dorsal-fin origin located slightly posterior to the middle of standard length. Base of last dorsal-fin ray anterior to or aligned with analfin origin. First dorsal-fin pterygiophore inserting behind neural spine of 10 th (1), 11 th (2) or 12 th* (1) vertebra. Adipose fin present. Anal-fin rays iv, 13 (1), 14 (5), 15 (15), 16 * (8), or 17 (1). Distal margin of anal fin slightly concave to nearly straight. First anal-fin pterygiophore inserting behind haemal spine of 19 th (2) or 20 th (1) vertebra. Pectoral-fin rays i, 10 (4), 11 * (20), or 12 (5). Tip of pectoral fin not reaching vertical through pelvic-fin insertion. Pelvic-fin rays i, 6 (1) or 7 * (29). Caudal fin forked, lobes rounded, similar in size. Principal caudal-fin rays 10 + 9 (3). Nine (2), 10 (1) or 11 * (1) dorsal procurrent caudal-fin rays, and 9 * (3) ventral procurrent caudal-fin rays. First gill arch with 7 (3) + 1 (3) + 10 (2) or 11 (1) rakers. Vertebrae 34 (1), 35 (1), 36 (1), or 37 *(1). Supraneurals 5 (3). Color in alcohol. Overall ground color tan, darker dorsally and yellowish ventrally. Dark chromatophores densely concentrated on dorsal surface of head from upper lip to supraoccipital spine. Small, dark chromatophores present over two first infraorbitals and anterior half to two-thirds of maxilla. Remaining infraorbitals and opercle usually with larger dark chromatophores. Area situated between ventral borders of infraorbitals and border of preopercle relatively clearer, with small chromatophores sparsely distributed. Ventral portion of head less pigmented, with scattered dark chromatophores more concentrated on anteromedian area. Scales of dorsal portion of body with dark chromatophores concentrated along its posterior margin resulting in a reticulate pattern; pattern usually reaching scale series immediately above pelvic-fin insertion. Central portion of scales with scattered, relatively large dark chromatophores, more densely distributed on dorsal half of body. Humeral region with a vertically-elongated, relatively narrow blotch not bordered anteriorly and posteriorly by clearer areas. Blotch extending over two horizontal series of scales above lateral line and one below it and covering one or one and a half scale from horizontal series above lateral line. Dark line poorly visible, extending from rear of humeral blotch to caudal peduncle. Relatively wide dark stripe on caudal peduncle, extending from area somewhat anterior to vertical through adipose fin or just below the fin and reaching the posterior border of four or five median caudal-fin rays. Abdominal region without dark chromatophores. All fin-rays darkened and small dark chromatophores scattered over clearer interradial membranes. Dorsal and anal fins somewhat darker. Anal fin of some specimens with higher concentration of dark chromatophores on distal border of rays. Pelvic fins hyaline or with few dark chromatophores forming interrupted lines over lateral borders of rays. Adipose fin darkened by small chromatophores. Darker specimens with higher concentration of chromatophores over whole body, all fins and interradial membranes, and humeral and caudal spots not clearly visible. Sexual dimorphism. Bony hooks on anal-fin rays were found in six male specimens examined (28.8– 42.8 mm SL). Hooks absent on remaining fins. Geographic distribution and ecological notes. Astyanax epiagos is known only from rio Ferro Doido, a tributary of rio Jacuípe, itself a tributary of the rio Paraguaçu, a coastal drainage of eastern Brazil (fig. 2). It was collected only above Cachoeira do Ferro Doido, a waterfall 98 meters high. According to extensive sampling efforts in other stretches of rio Ferro Doido the species is apparently absent below the waterfall and, indeed, absent in all others streams of Paraguaçu basin sampled. The species was collected exclusively in dark water streams, running over rocky bottom at elevate altitudes (899–934 m), in environment characterized by relatively small rocky pools (0.5 m deep and 1.5 m wide) connected by extremely shallow stretches of water or small rapids (fig. 3). The surrounding vegetation is characteristic of ‘Campo Rupestre’, with predominance of herbs and shrubs. The unique fish species collected with A. epiagos and known to occur in the region is Hoplerythrinus unitaeniatus. The analysis of the stomach contents of six specimens revealed the presence of filamentous algae, fragments of vascular plants, adults and two distinct larvae of Diptera (Chironomidae), adults of Hemiptera and Coleoptera (Chrysomelidae), fragments of Hymenoptera and of other unidentified arthropods. Popular name. Piaba. Etymology. The name epiagos from the Greek, epi for above, and agos meaning rocky cleft, refers to the presence of the species on area above the waterfall and valley formed by rio Ferro Doido.Published as part of Zanata, Angela M. & Camelier, Priscila, 2008, Two new species of Astyanax (Characiformes: Characidae) from upper rio Paraguaçu and rio Itapicuru basins, Chapada Diamantina, Bahia, Brazil, pp. 28-40 in Zootaxa 1908 on pages 29-33, DOI: 10.5281/zenodo.27453

Astyanax jacobinae Zanata & Camelier, 2008, new species

Astyanax jacobinae, new species Figs. 4, 5 Holotype. MZUSP 89570 (50.8 mm SL), Brazil, Bahia, Jacobina, Itaitu village, rio da Jaqueira below Cachoeira Araponga, tributary of rio Itapicuru-mirim, rio Itapicuru basin, 11 ° 22 ’ 19.8 ’’N, 40 ° 29 ’ 39.7 ’’W, 535 m alt.; Zanata et al., 13 June 2005. Paratypes. Collected with holotype. UFBA 0 2793 (5, 22.8–38.2 mm SL; 1 c&s, 32.2 mm SL). MZUSP 89571 (3 R, 27.1 –32.0 mm SL). Diagnosis. Astyanax jacobinae can be distinguished from most of its congeners and from all other Astyanax species known from northeastern Brazilian drainages (A. brevirhinus, A. fasciatus, A. intermedius, A. lacustris, A. pelecus, A. rivularis, A. taeniatus) by the presence of a vertically elongated humeral blotch (vs. distinctly horizontally elongated humeral blotch in A. lacustris and A. pelecus), absence of a conspicuous dark stripe from humeral region to caudal peduncle (vs. well defined dark midlateral stripe along most of body length in A. intermedius, A. pelecus, A rivularis, A. taeniatus), three or four outer premaxillary teeth, three maxillary teeth, and 21–26 anal fin rays (vs. five outer premaxillary teeth, one or two maxillary teeth, and 28 anal-fin rays in A. brevirhinus). The new species differs from the majority of Astyanax species by its larger eye diameter (36.8–40.3 % vs. 24.7–35.4 %, with the exception of A. intermedius among northeastern species that approaches the eye diameter of A. jacobinae with 29.0– 36.4 %). Astyanax jacobinae can be further distinguished from A. intermedius by having higher number of branched anal-fin rays (19–22 vs. 16–18), shorter distance from snout to anal-fin origin (61.4–64.4 % vs. 66.2–68.3 %), and longer anal-fin base length (27.6– 30.7 % vs. 21.6–24.8 %). Can be further distinguished from A. rivularis by having lower number of perforated scales (34–37 vs. 39) and three maxillary teeth (vs. one or two). Also differs from A. taeniatus by having three maxillary teeth (vs. two) and by having lower number of cusps on teeth (usually five vs. usually seven cusps, even on maxillary teeth). Astyanax jacobinae can be further diagnosed from specimens of A. fasciatus from São Francisco and Paraná rivers by the absence of a conspicuous caudal blotch, by having three maxillary teeth, and dentary teeth decreasing gradually in size (vs. presence of a well defined caudal blotch, one maxillary teeth, and dentary with four larger teeth followed by a number of small ones). This new species distinguishes from A. turmalinensis by its higher number of maxillary teeth and by the presence of only one humeral blotch (3 or 4 teeth vs. 1 or 2 and presence of two humeral blotches). It can be also distinguished from A. epiagos by having higher number of branched anal-fin rays (19–22 vs. 13–17), three maxillary teeth (vs. 0–2), longer anal-fin base length (27.6–30.7 % vs. 18.1–23.2 %), shorter distance from eye to dorsal-fin origin (36.0– 39.2 % vs. 39.5–43.2 %), and also by the absence of broad space between infraorbitals and preopercle (see under ‘Discussion’ for diagnosis of the species from “ A. scabripinnis species complex”). Description. Morphometric data of the holotype and paratypes are presented in Table 1. Body compressed, moderately elongate. Greatest body depth located along vertical through posterior portion of pectoral fin. Dorsal profile of head convex from upper lip to vertical through anterior nostrils; straight to slightly concave from latter point to tip of supraoccipital spine and convex from this point to dorsal-fin origin. Body profile along dorsal-fin base straight and posteroventrally inclined; straight from dorsal-fin base terminus to adipose fin; slightly concave between latter point to origin of dorsalmost procurrent caudal-fin ray. Ven t ra l profile of body convex from tip of lower lip to anal-fin origin. Body profile along anal-fin base straight and posterodorsally inclined. Ventral profile of caudal peduncle nearly straight to slightly concave. Mouth terminal. Posterior terminus of maxilla extending beyond anterior margin of orbit. Premaxillary and dentary teeth massive, cusps distributed in a gently arch facing oral cavity. Premaxillary teeth in two rows. Outer row with 3 * (8) or 4 (1) teeth bearing 3 or 5 cusps. Inner row with 5 (9) teeth bearing 4 to 7 cusps. Symphyseal tooth of inner series asymmetrical, with one cusp on anteromedial side, one larger central cusp and two smaller on lateral side, second teeth the larger, with 7 cusps in the holotype, followed by teeth with 5 cusps; smaller specimens with a maximum of 5 cusps. Maxilla with 3 (9) teeth bearing 5 cusps; teeth similar in size. Dentary with 11 (1) or 12 * (1) symmetrical teeth; anteriormost ones broad and similar in size, with 5 or 7 cusps, followed by teeth with 5 cusps and posterior teeth with 1 or 3 cusps. Dentary teeth decreasing gradually in size and number of cusps posteriorly. Scales cycloid, circuli absent on exposed area of scales, with various divergent radii extending to posterior margin of scales. Lateral line slightly decurved anteriorly, completely pored from supracleithrum to base of caudal fin, with 35 * (3), 36 (3), or 37 (1) perforated scales. Horizontal scale rows between dorsal-fin origin and lateral line 5 (2) or 6 * (5), not including scale of predorsal series situated just anterior to first dorsal-fin ray. Horizontal scale rows between lateral line and pelvic-fin insertion 4 * (7). Scales along middorsal line between tip of supraoccipital process and origin of dorsal fin 11 * (6) or 12 (1). Horizontal scale rows around caudal peduncle 13 (2) or 14 * (3). Single row of 3 to 5 scales covering base of anterior most anal-fin rays. Dorsal-fin rays ii, 9 (9). Distal margin of dorsal fin straight. Dorsal-fin origin located slightly posterior to or on the middle of standard length. Base of last dorsal-fin ray aligned with vertical through anterior branched anal-fin rays. First dorsal-fin pterygiophore inserting behind neural spine of 11 th* (2) vertebra. Adipose fin present. Anal-fin rays iv, 19 * (3), 20 (4), 21 (1), or 22 (1). Distal margin of anal fin concave. First anal-fin pterygiophore inserting behind haemal spine of 17 th * (3) or 18 th (2) vertebra. Pectoral-fin rays i, 10 * (3) or 11 (6). Contact of posterior extremity of pectoral and pelvic-fin insertion ontogenetically variable; pectoral fin not reaching vertical through pelvic-fin insertion of holotype but trespassing that point in specimens of 38.2 mm SL or smaller. Pelvic-fin rays i, 6 * (3) or 7 (6). Caudal fin forked, lobes rounded, similar in size. Principal caudal-fin rays 10 + 9 (5). Eleven * (1) or 12 (1) dorsal procurrent caudal-fin rays and 8 (2) or 9 * (2) ventral procurrent caudal-fin rays. First gill arch with 5 (1) + 1 (1) + 10 (1) rakers. Vertebrae 35 * (3) or 36 (2). Supraneurals 5 * (2) or 6 (1). Color in alcohol. Ground color tan, usually ventral and dorsal half of body similarly darkened. Dark chromatophores densely concentrated on dorsal surface of head from upper lip to supraoccipital spine. Middorsal portion of body dark. Small, dark chromatophores present on snout, entire maxilla and on portion of infraorbitals closer to the orbit. Distal portions of infraorbitals, mainly on third infraorbital, and areas of preopercle and opercle with relatively larger, scattered dark chromatophores. Ventral portion of head less pigmented, with scattered dark chromatophores spread throughout. Scales of lateral portion of body with dark chromatophores almost homogeneously distributed over entire area, not forming a conspicuous reticulate pattern. Central portions of scales usually with smaller chromatophores. Region comprised below lateral line, between cleithrum and anal-fin origin, slightly clearer. Humeral region with a vertically-elongated blotch, extending from two horizontal series of scales above lateral line to about one or one and a half scales below it. Humeral blotch bordered anteriorly and posteriorly by clearer areas. Caudal peduncle with inconspicuous dark mark, more visible in specimens around 30.0 mm SL. Dorsal, anal, and caudal fins darkened. Dorsal and caudal fins with dark chromatophores somewhat homogeneously distributed over rays and interradial membranes. Anal fin darkened in a pattern similar to that of dorsal fin, but with dark pigmentation distinctly more developed over interradial membranes and on borders of rays. Pectoral and pelvic fins clearer, with dark chromatophores only over borders of rays. Adipose fin covered with small dark chromatophores. Caudal fin with dark chromatophores somewhat more concentrated on median four or five rays, but not configuring a well defined stripe. Color in life. Freshly collected specimens had overall coloration silvery-tan, with silvery highlights on scales, major portion of iris, infraorbitals, preopercle, and opercle (fig. 5). Dorsal portion of iris, together with lateroventral half of head, with the exception of third infraorbital, and ventral portion of preopercle and opercle tinged with yellow. Scales around humeral spot and on lateroventral region of body anterior to anal fin origin also yellowish. Humeral spot visible, although not so conspicuous as in preserved specimens. Concentration of dark chromatophores visible over caudal peduncle, although not forming conspicuous blotch. Dorsal, anal, caudal, and adipose fins reddish-orange. Pectorals yellowish and pelvic fins hyaline. Sexual dimorphism. Bony hooks on fins or other dimorphic characters were not found in the specimens examined. Geographic distribution and ecological notes. Astyanax jacobinae was collected only in rio da Jaqueira, below Cachoeira Araponga (11 ° 22 ’ 19.8 ’’N, 40 ° 29 ’ 39.7 ’’W), a tributary of rio Itapicuru-mirim, rio Itapicuru basin (fig. 2). The type-locality of A. jacobinae is a dark headwater stream with mild water current running over pebbles, rocks and sand (fig. 6). Stream depth in the area sampled varied between 0.3–0.5 m and average width was around 2.0 m. Trees, palm trees, and grasses represented the marginal vegetation. The analysis of the stomach contents of one specimen revealed the presence of two distinct larvae of Diptera (Chironomidae), larvae of Trichoptera, fragments of adults of Diptera and unidentified fragments of arthropods. Popular name. Piaba. Etymology. The name jacobinae refers to the type locality, município de Jacobina, BA, Brazil.Published as part of Zanata, Angela M. & Camelier, Priscila, 2008, Two new species of Astyanax (Characiformes: Characidae) from upper rio Paraguaçu and rio Itapicuru basins, Chapada Diamantina, Bahia, Brazil, pp. 28-40 in Zootaxa 1908 on pages 34-36, DOI: 10.5281/zenodo.27453

Characidium summus Zanata & Ohara, 2015, new species

<i>Characidium summus</i>, new species <p>(Fig. 1 a)</p> <p> <b>Holotype.</b> MZUSP 116954, 34.5 mm SL, Brazil, Rondônia, Guajará-Mirim, upper rio Pacaás Novos, tributary of rio Mamoré, rio Madeira basin, 10º50'46.29"S 63º37'47.29"W, D. Hungria & A.C. Ribeiro, 17 Dec 2013.</p> <p> <b>Paratypes.</b> MZUSP 116105, 11, 1 CS, 14.0– 42.3 mm SL; MNRJ 42909, 3, 25.6–39.4 mm SL; INPA 46986, 3, 28.2–30.9 mm SL; UFRO 23255, 2, 14.3–29.2 mm SL, collected with holotype.</p> <p> <b>Diagnosis.</b> <i>Characidium summus</i> is a unique species among congeners by lacking an adipose fin and having a complete lateral line. It can be further distinguished from congeners, including <i>C. vestigipinne</i> Buckup & Hahn, that have complete lateral line and adipose fin absent, vestigial or reduced by the absence of dark bars or spots on head, body or fins, except for a dark blotch immediately on the rear of opercle, a narrow midlateral dark stripe (less than half scale deep), and a dark basicaudal spot.</p> <p> <b>Description.</b> Morphometric data of holotype and paratypes presented in Table 1. Body fusiform and moderately compressed. Greatest body depth at vertical through dorsal-fin origin. Dorsal profile convex from upper lip to vertical through nares, slightly convex to nearly straight from this point to end of occipital process, slightly convex to nearly straight from this point to origin of dorsal-fin base, slightly convex along dorsal-fin base, and nearly straight from end of dorsal-fin base to origin of anteriormost dorsal procurrent caudal-fin ray. Vent ral profile straight to slightly convex from anterior portion of head to pelvic-fin origin, straight from latter point to origin of anal fin, straight and posterodorsally slanted along anal-fin base and straight along caudal peduncle. Snout triangular-shaped in lateral view. Mouth subterminal, slightly more dorsal than ventral edge of orbit. Distal tip of maxilla surpassing anterior margin of orbit. Orbit rounded, horizontal length longer than snout length. Cheek thin, its depth around a third to a quarter of orbit diameter. Nares separated; anterior naris with raised margins; posterior naris considerably closer to orbit than to anterior naris, without skin flaps. Supraorbital reduced to a minute ossification on anterodorsal portion of eye (Fig. 2). Nasal bones restricted to the ossified canal, without lateral lamella. Parietal fontanel limited anteriorly by frontals. Parietal branch of supraorbital canal present, not reaching frontal-parietal border. Epiphyseal branch of supraorbital canal absent.</p> <p>Dentary teeth in two rows; outer series with 10(1) or 12(1) conical teeth; teeth decreasing in size from symphysis; inner series, with around 15 minute conical teeth inserted on edge of replacement tooth trench. Dentary teeth usually inclined anteriomedially; distal portion of symphyseal tooth overlapping its contralateral in some specimens. Premaxilla with a single series of 7(2), 8*(12), 9(2), or 10(1) conical teeth, decreasing in size from symphysis. Maxillary edentulous. Ectopterygoid teeth 6(1), conical, distributed in one series. Mesopterygoid teeth absent.</p> <p> Scales cycloid; <i>circulii</i> absent and around 25 <i>radii</i> present on posterior field of scales. Lateral line complete, perforated scales 35(3), 36*(11), or 37(3); total horizontal scale rows above lateral line 4*(15) or 5(2); horizontal scale rows below lateral line 5*(14) or 6(2). Scales along middorsal line between supraoccipital and origin of dorsal fin around 15, but mostly disordered. Scales rows around caudal peduncle 14*(17). Axillary scale absent. Isthmus completely scaleless, but area between pectoral fins covered by scales. Pseudotympanum present, represented by small muscular hiatus at vertical through anterior portion of the swimbladder; hiatus situated between ribs of fifth and sixth vertebrae (Fig. 3).</p> <p>Dorsal-fin rays ii,9(3), 3,i,8(1), or 3,i,9*(13); distal margin of dorsal fin rounded. Dorsal-fin origin at middle of standard length and slightly anterior to vertical through pelvic-fin origin. Adipose fin absent (20). Pectoral-fin rays highly variable iii,6,i(2), iii,6,ii(2), iii,7,i(2), iii,8,i(1), iii,8,ii(1), iv,6,i(1), iv,6,i(2), iv,7(4), or 4,i,8*(1); 1st and 2nd branched pectoral-fin rays longest; posterior tip of pectoral fin not reaching pelvic-fin insertion. Pelvic-fin rays i,6,i*(16), or i,7(1); 2nd and 3rd branched pelvic-fin rays longest; posterior tip of pelvic fin not reaching anal-fin origin. Anal-fin rays ii,6*(15), iii,6(1), and iv, 5 in the CS specimen; posterior margin of anal fin rounded. Caudalfin rays i,7,8,i(1), i,8,8,i*(15), or i,9,9,i(1). Caudal fin forked, lobes somewhat pointed, of similar size. Dorsal procurrent caudal-fin rays 9(1); ventral procurrent caudal-fin rays 9(1).</p> <p>Total number of vertebrae 36(1); precaudal vertebrae 21(1); caudal vertebrae 15(1). Supraneural bones 4(1), similar in size. Epural bones 3(1). Uroneural bones 1(1). Branchiostegal rays 4(1); 3 connected to anterior ceratohyal, 1 connected to area between anterior and posterior ceratohyal.</p> <p> <b>TABLE I.</b> Morphometric data of holotype and paratypes of <i>Characidium summus</i> (number of specimens measured = 17). The range includes the holotype. SD = standard deviation.</p> <p> <b>Color in alcohol.</b> Ground color of head and body light brown (Fig. 1 a). Head with minute melanophores homogeneously distributed over dorsal and ventral portion, not forming spots. Body similarly colored, usually slightly darker on dorsal half. Some specimens with inconspicuous reticulate pattern on dorsal half of body due to light concentration of melanophores on posterior margin of scales. Dark midlateral narrow stripe (less than half scale deep) usually extending from rear of opercle to caudal peduncle, but not reaching its end or the basicaudal spot. Dark blotch immediately at rear of opercle, over two first scales of the lateral line and formed by pigment on skin; blotch somewhat round in most specimens. Smallest specimen examined without dark stripe and anterior blotch. Vertical dark bars on body absent (n=19); one specimen with very inconspicuous vertical blotches below dark midlateral stripe on first half of body. Basicaudal black spot conspicuous and well defined, somewhat vertically elongated, occupying area on the base of 4–6 caudal-fin rays; small specimens with basicaudal spot distinctly black. Fins similarly colored to each other, with melanophores over rays; interradial membranes hyaline; paired and anal fins somewhat less pigmented on its distal half.</p> <p> <b>Etymology.</b> From the Latin <i>summus</i>, which means high, elevated, alluding to the high altitude where the species occurs, near Pico Tracoá, higher than 1100 m above sea level in the Serra dos Pacaás Novos.</p> <p> <b>Sexual dimorphism.</b> No hooks on fins or other sexually dimorphic features were observed externally on the specimens examined.</p> <p> <b>Distribution.</b> The new species is only known from upper rio Pacaás Novos, a tributary of rio Mamoré, rio Madeira basin, Rondônia State, Brazil (Fig. 4).</p> <p> <b>Habitat and ecological notes.</b> <i>Characidium summus</i> occurs in a headwater of the rio Pacaás Novos, at 920 meters above sea level, situated on the Serra dos Pacaás Novos, close to the highest peak of the Rondônia State, named Pico Tracoá, higher than 1100 m. The type locality of <i>C. summus</i> is within the Conservation Unit Parque Nacional de Pacaás Novos, situated in the central portion of Rondônia State. The rio Pacaás Novos is a black water river, with moderate water current and predominantly rocky bottom. Specimens of <i>C. summus</i> were sampled in small puddles (1–4 m wide and 1.5 m deep) and laterally in the river backwaters, with water temperature of 22ºC, pH 3.58, dissolved oxygen 7mg /L, satured oxygen 16%, and conductivity 10µm/cm. Only juveniles of <i>Erythrinus erythrinus</i> (Bloch & Schneider) were sampled syntopically with the new species. Both species have color pattern and general shape of the body remarkably similar (Fig. 1 b).</p> <p> <b>Remarks.</b> <i>Characidium summus</i> does not fit into any group of <i>Characidium</i> previously proposed in the literature (e.g., Buckup & Reis, 1997; Buckup & Hahn, 2000; Graça & Pavanelli, 2008; Netto-Ferreira <i>et al.</i>, 2013). The unique potential synapomorphy shared with clades within <i>Characidium</i> proposed by Buckup (1993b) is the scaleless isthmus, one of the features of the Clade C1. The absence of adipose fin is shared with <i>C. mirim</i> Netto-Ferreira, Birindelli & Buckup, <i>C. nupelia</i> da Graça, Pavanelli & Buckup, <i>C. stigmosum</i> Melo & Buckup, <i>C. xavante</i> da Graça, Pavanelli & Buckup, and <i>C</i>. <i>vestigipinne</i>. However, according to the hypothesis of Netto- Ferreira <i>et al.</i> (2013), these species belongs to the Clade C4, supported by two synapomorphies not observed in <i>Characidium summus</i>: absence of the parietal branch of the supraorbital canal and absence of the inner row of teeth on dentary. Furthermore, the new species does not share the incompleteness of lateral line or color patterns of <i>C. mirim</i>, <i>C. nupelia</i>, <i>C. stigmosum</i>, and <i>C. xavante</i>. The combination of adipose fin absent and lateral line complete occurs occasionally in specimens of <i>C</i>. <i>vestigipinne</i>. According to the original description, in <i>C. vestigipinne</i> the adipose fin can be absent, vestigial or reduced in size (Buckup & Hahn, 2000). However, as stated above, the latter species is a member of the Clade C4, closely related to <i>C. rachovii</i> Regan, <i>C. stigmosum, C. occidentale</i> Buckup & Reis, and <i>C. orientale</i> Buckup & Reis, sharing presence of a dark band along distal margin of anal and pelvic fins in adult males (Netto-Ferreira <i>et al</i>., 2013).</p> <p> A noteworthy condition for a species of <i>Characidium</i> observed in <i>C. summus</i> is the almost complete absence of supraorbital (Fig. 2). In fact, a minute vestigial supraorbital occurs. Loss of supraorbital was used to defined suprageneric relationships within characidiins and proposed as one of the three synapomorphies supporting the sister-group relationship of <i>Microcharacidium</i> and <i>Odontocharacidium</i>, the hypothesis B of Buckup (1993b). The other two synapomorphies are loss of postcleithrum 1 and complete loss of lateral tooth cusps, the former not occurring in <i>C. summus</i> and the latter present. Although having a vestigial supraorbital, a feature not observed in congeners, <i>C. summus</i> possess the conspicuous basicaudal dark spot and overall body morphology similar to the species included in <i>Characidium</i>.</p> <p> The new species possesses a remarkably small pseutotympanun when compared to the structure described recently for <i>C</i>. <i>bahiense</i> Almeida, <i>C. bimaculatum</i> Fowler, <i>C. samurai</i> Zanata & Camelier, and <i>C. timbuiense</i> Travassos (Zanata & Camelier, 2014) and other species examined herein for this feature. In <i>C. summus</i>, the pseudotympanum is barely or not visible externally by transparency. After removal of the skin the aperture observed is elongate and narrow, positioned between ribs of the fifth and sixth vertebrae, which remain concealed (Fig. 3). The opposite condition, with pseudotympanum visible through body wall and represented by a distinctly large aperture, usually with portions of two ribs exposed, occurs in species of <i>Characidium</i> with a reduced lateral line (e.g., <i>C. bahiense</i>, see Zanata & Camelier, 2014: fig 3). This is the case in <i>C. mirim</i> and <i>C. xavante</i>, both with pseudotympana similar to <i>C. bahiense</i> but with an even larger aperture, most of the hiatus situated between ribs of the fifth and sixth vertebrae plus a small opening anterior to the rib of fifth vertebra or posterior to the rib of the sixth vertebra. <i>Characidium nupelia</i> and <i>C. stigmosum</i> also possess similar pseudotympana, although with aperture slightly smaller.</p> <p> According to Bockmann & Castro (2010), a large and widely exposed pseudotympanum seems to be characteristic of small-sized otophysan fishes, which inhabit calm waters, including a few species of <i>Characidium</i>. Comparisons of aspects of the pseudotympanum and lateral line completeness in species of <i>Characidium</i> inhabiting lotic and lentic environments reveal possibly related characters. As discussed above, examined species of <i>Characidium</i> with lateral line incomplete also possess a widely exposed pseudotympanum and inhabit relatively calm waters (e.g., <i>C. bahiense, C. mirim, C. nupelia, C. xavante</i>, and <i>C. stigmosum</i>), and congeners inhabiting moderate to fast running waters possess a complete lateral line and comparatively smaller pseudotympanum (e.g., <i>C. bimaculatum</i>, <i>C. samurai</i>, <i>C. summus</i>, and <i>C. timbuiense</i>). However, clear-cut criteria to indicate the degree of dependence between these features are lacking; confirmation of the hypothesis presented herein depends on future studies.</p> <p> <i>Characidium summus</i> apparently is a moderate water current dwelling fish and does not possess adaptations cited by Buckup <i>et al</i>. (2000) for congeners that inhabit fast water current environments, as a streamlined body and paired-fins modifications. Rather, somewhat fragile paired fins and a somewhat truncated body are observed in the new species. As informed elsewhere, only juveniles of <i>Erythrinus erythrinus</i> were sampled syntopically with <i>C. summus</i>. Both species have a color pattern and general body shape remarkably similar (Fig. 1 a, b), interpreted herein as a putative mimetic association among them. Mimetic relations involving <i>Characidium</i>, particularly <i>C. heirmostigmata</i>, was previously proposed by Tencatt <i>et al</i>. (2014) in the description of the syntopic catfish <i>Corydoras lacrimostigmata</i> Tencatt, Britto & Pavanelli, 2014. According to the authors, both species possess resemblance in color pattern and form of caudal-fin lobes, more rounded in <i>C. lacrimostigmata</i> than in congeners and very similar to the caudal-fin lobes of <i>C. heirmostigmata</i>. <i>Erythrinus erythrinus</i> possess widespread distribution, predatory habits, and a somewhat similar coloration pattern throughout South America (Oyakawa <i>et al</i>., 2013), possibly representing a model of Batesian mimicry. <i>Characidium summus,</i> on the other hand, is apparently narrowly distributed, possess distinct color pattern from congeners, and possibly represents the mimic in the association. Previous mimetic relations involving <i>E. erythrinus</i> were described by Brosset (1997). However, that is a case of aggressive mimicry where <i>E. erythrinus</i> plays the mime and <i>Laimosemion agilae</i> (Hoedeman) the model, in a male-oriented mimicry. Understanding the ecological relationships between <i>C. summus</i> and <i>E. erythrinus</i> is critical to assess its ecological significance and the possible evolutionary process involved in the association.</p> <p> <b>Comparative material examined.</b> All from Brazil, except when noted. <i>Characidium alipioi</i>: MNRJ 5550, holotype, 50.0 mm SL, Rio de Janeiro, rio Paraíba do Sul basin; MNRJ 5551, paratype, 51.0 mm SL; MNRJ 5552, paratype, 48.3 mm SL; MNRJ 5553, paratype, 45.0 mm SL. MZUSP 112331, 6, 50.3–72.3 mm SL, São Paulo, rio Paraíba do Sul basin. MZUSP 80224, 12, 36.5–61.9 mm SL, Rio de Janeiro, rio São João basin. <i>Characidium bahiense</i>: MZUSP 8940, holotype, 16.0 mm SL, Bahia, Arembepe; MZUSP 8923, paratype, 18.7 mm SL; MZUSP 8924, paratype, 21.5 mm SL. UFBA 7167, 23, 3 CS, 21.1–26.0 mm SL, Bahia, rio Itapicuru basin. <i>Characidium bimaculatum</i>: MNRJ 21249, 14, 20.5–41.4 mm SL, Ceará, rio Curu basin. MNRJ 4925, 1, 25.5 mm SL; MNRJ 4928, 1, 28.7 mm SL, Ceará, rio Salgado basin. MZUSP 110779, 8, 29.4– 24.3 mm SL, Paraíba, rio Acaraú basin.</p> <p> UFBA 3829, 6, 1 CS, 22.5–30.8 mm SL, Paraíba, rio Piranhas basin. MZUSP 68959, 1 CS, 22.2 mm SL, Rio Grande do Norte, rio Ceará-Mirim. <i>Characidium</i> cf. <i>declivirostre</i>: MZUSP 97137, 1, 35.4 mm SL, Pará, rio Xingu basin. MZUSP 82084, 2, 44.5–46.5 mm SL, Mato Grosso, rio Juruena basin. MZUSP 84965, 1CS, 43.8 mm SL, Amazonas, rio Negro basin. <i>Characidium etheostoma</i>: MZUSP 96860, 2CS, 40.7–47.1 mm SL, Pará, rio Xingu basin. <i>Characidium fasciatum</i>: MZUSP 39676, 15, 32.7–36.4 mm SL, Minas Gerais, rio São Francisco basin. <i>Characidium gomesi</i>: MZUSP 73193, 47, 25.8–32.0 mm SL, Minas Gerais, rio Paranaíba basin. MZUSP 88440, 3, 29.5–42.8 mm SL, São Paulo, rio Corumbataí. MZUSP 98815, 1CS, 52.4 mm SL, São Paulo, rio Tietê. <i>Characidium grajahuensis</i>: MNRJ 3855, holotype (snout damaged, precise measurement currently not possible), Rio de Janeiro, Grajaú. <i>Characidium hasemani</i>: MZUSP 91785, 4, 44.0–58.0 mm SL, Mato Grosso, rio Xingu basin. <i>Characidium heirmostigmata</i>: MZUSP 97738, holotype, 34.6 mm SL, Paraná, rio Paraná basin. <i>Characidium interruptum</i>: MZUSP 58992, 1, 30.9 mm SL, Rio de Janeiro, rio São João basin. <i>Characidium japuhybense</i>: MNRJ 5194, holotype (snout damaged, precise measurement currently not possible), Rio de Janeiro, Angra dos Reis. <i>Characidium lagosantense</i>: MNRJ 3852, holotype (snout damaged, precise measurement currently not possible), Minas Gerais, rio São Francisco basin. MNRJ 18108, 71, 11.2–31.2 mm SL, Minas Gerais, rio São Francisco basin. <i>Characidium lanei</i>: MNRJ 6185, holotype, 40.8 mm SL, São Paulo, rio Ribeira do Iguape basin; MNRJ 9766, paratype, 36.2 mm SL. MNRJ 32884, 38, 20.9–36.4 mm SL, São Paulo, rio Lajeado. MZUSP 69585, 7, 25.2–31.0 mm SL, São Paulo, rio Ribeira do Iguape basin. <i>Characidium laterale</i>: MZUSP 90204, 2, 20.6–25.1 mm SL, Mato Grosso, rio Paraguai basin. MZUSP 96687, 80, 15.7–24.0 mm SL, Mato Grosso, rio Paraguai basin. <i>Characidium lauroi</i>: MNRJ 5529, holotype, 60.4 mm SL, Rio de Janeiro, rio Paraíba do Sul basin; MNRJ 5530, paratype, 56.8 mm SL. MZUSP 110359, 5, 31.1–45.9 mm SL, São Paulo, rio Paraíba do Sul basin. <i>Characidium mirim</i>: MZUSP 97724, paratypes, 4, 18.9–19.7 mm SL, Mato Grosso, rio Araguaia basin. <i>Characidium nupelia</i>: MZUSP 87743, holotype, 29.0 mm SL, Mato Grosso, rio Paraguai basin. <i>Characidium oiticicai</i>: MNRJ 9480, holotype, 35.3 mm SL, São Paulo, rio Tietê basin. MZUSP 108640, 2, 37.4–38.1 mm SL, São Paulo, rio Tietê basin. MZUSP 26973, 5CS, 37.4–51.3 mm SL, São Paulo, rio Tietê basin. <i>Characidium</i> cf. <i>pteroides</i>: MZUSP 85653, 81, 16.3–28.7 mm SL, Amazonas, rio Negro basin. <i>Characidium pterostictum</i>: MZUSP 43547, 15, 28.7–37.8 mm SL, Rio Grande do Sul, Mampituba system. <i>Characidium rachovii</i>: MZUSP 49163, 8, 25.9–34.2 mm SL, Rio Grande do Sul, lagoa dos Patos drainage. MZUSP 49172, 1CS, 26.9 mm SL, Rio Grande do Sul, rio Grande. <i>Characidium samurai:</i> MZUSP 108188, holotype, 46.6 mm SL, Bahia, rio das Almas basin; MZUSP 112385, paratypes, 9, 1 CS, 25.4–42.7 mm SL; UFBA 7259, paratypes, 7, 20.8–42.6 mm SL, collected with holotype. <i>Characidium stigmosum</i>: MZUSP 40804, holotype, 33.5 mm SL, Goiás, rio Tocantins basin. <i>Characidium tenue</i>: MZUSP 63803, 6, 31.0– 42.2 mm SL, Rio Grande do