Microschemobrycon cryptogrammus, Ohara & Jerep & Cavallaro, 2019

Ohara, Willian M., Jerep, Fernado C. & Cavallaro, Marcel R., 2019, A new species of Microschemobrycon (Characiformes: Characidae) from Rio Xingu basin, Brazil, Zootaxa 4576 (2), pp. 326-336 : 327-332

Microschemobrycon cryptogrammus , new species

( Figs. 1–2 )

Holotype. MZUSP 123748 , 23.6 mm SL, Brazil, Pará State, Altamira, igarapé tributary of Rio Curuá , Rio Xingu basin, 15 km north from Castelo dos Sonhos, 8°10'25"S 55°7'43"W, 0 8 Aug 2015, W. M. Ohara, M. Pastana & O. Oyakawa.

Paratypes. All from Brazil, Pará State, Altamira , Rio Xingu basin, Rio Curuá drainage. MZUSP 119370 , 5 , 19.5 – 21.7 mm SL, same data as holotype. MZUSP 116013 , 5 , 20.7 – 22.5 mm SL (2 c&s, 20.9–22.5 mm SL), tributary of igarapé Treze de Maio , 8°39'08"S 55°02'08"W, 5 Nov 2014, W. M. Ohara & J. Bilce. MZUSP 116046 , 16 , 20.1 – 23.5 mm SL, igarapé tributary of Rio Curuá , 8 km from Cachoeira da Serra , 8°36'19"S 55°5'28"W, 5 Nov 2014, W. M. Ohara & J. Bilce. MNRJ 34800 , 6 , 18.0– 22.2 mm SL, igarapé tributary of Rio Curuá , 8°10'52"S 55°7'33"W, 30 Sep 2008, M. Britto, J. Gomes, F. Carvalho & L. Fries. MZUSP 119647 , 1 , 20.7 mm SL, tributary of Rio Curuá , 10 km of Castelo dos Sonhos, 8°21'9"S 55°10'16"W, 0 7 Aug 2015, W. M. Ohara, M. Pastana & O. Oyakawa .

Diagnosis. The new species is distinguished from all Aphyoditeinae (sensu Lima et al., 2017) by the presence of a unique well-defined, rounded dark caudal-peduncle blotch and by a subjacent dark midlateral stripe visible in live specimens; and from all Characinae (sensu Mirande, 2018) by the presence of a single row of perfectly aligned, similarly-sized tricuspid teeth in the premaxilla and dentary. Furthermore, Microschemobrycon cryptogrammus can be distinguished from all Microschemobrycon species, except M. elongatus , by the presence of a longitudinal dark stripe along the lower jaw. The new species can be distinguished from M. elongatus by having lateral line with 36–38 pored scales (vs. lateral line with 15–19 pored scales); by the presence of anterior and posterior nostrils separated by narrow skin fold (vs. nostrils distinctly separated, as illustrated by Géry (1973: 98, Fig. 10); dark chromatophores concentrated along ventral margin of the caudal peduncle (vs. pigmentation absent); and by the presence in life of a dark spot at base of dorsal-fin origin (vs. absent). Additionally, M. cryptogrammus can be distinguished from M. callops by the absence of a humeral blotch (vs. vertically elongated humeral blotch present) and by presenting a hyaline dorsal fin (vs. dorsal fin with a dark crescent-shaped blotch); from M. casiquiare by the number of perforated scales in the lateral line (33–38 vs. 15–26); from M. geisleri by the absence of humeral blotch (vs. presence of a rounded humeral blotch); from M. guaporensis by the absence of two crescent shaped brown marks over the distal margin of hypurals (vs. presence); from M. meyburgi by the presence of 33–38 pored scales in the lateral line (vs. 3–5) and tricuspid teeth on jaws (vs. unicuspid); and from M. melanotus by the absence of dorsal-fin blotch (vs. dorsal-fin blotch present) and by presenting a terminal mouth (vs. mouth slightly upturned).

Description. Morphometric data of the new species presented in Table 1. Body elongated and compressed; greatest body depth at vertical through dorsal-fin origin. Dorsal profile of head slightly convex from snout to vertical through anterior border of posterior nostril, straight to slightly convex from that point to dorsal-fin origin. Dorsal-fin base slightly convex, descending posteriorly. Dorsal profile from last dorsal-fin ray to adipose-fin base straight to slightly convex, slightly concave from latter point to caudal-fin origin. Ventral profile of head and anterior region of body slightly convex from mouth to genital papilla; straight to slightly concave along anal-fin base. Ventral profile of caudal peduncle straight to slightly concave.

Pseudotympanum present, roughly oval, bordered dorsally by lateralis superficialis muscle, antero-ventrally by obliquus superioris muscle, postero-ventrally by obliquus inferioris muscle, posteriorly by anterior face of second pleural rib, postero-dorsally by obliquus superioris muscle.

Mouth terminal, opening at horizontal line through ventral border of eye pupil. Anterior and posterior nostrils separated by narrow skin fold (see similar condition in Géry, 1973; 88, Fig. 4 ). Maxilla short, posteroventrally angled, posterior terminus falling short from vertical through anterior margin of eye and surpassing ventrally horizontal through ventral margin of eye. Teeth elongated, similar in shape. Premaxilla with 11(2), tricuspid teeth aligned in single row. Maxilla with 5(2) teeth with 1-3 cusps. Dentary with 15–17(2) tricuspid or conical teeth decreasing in size posteriorly.

Dorsal-fin rays ii,7(1) or ii,8*(18). First unbranched dorsal-fin ray half length of second unbranched ray. First branched ray as long as second unbranched ray, subsequent branched rays gradually decreasing in size posteriorly. Dorsal-fin origin slightly anterior to mid-body standard length. First dorsal-fin pterygiophore located posterior to neural spine of 9 th (2) vertebrae. Adipose-fin origin at vertical through base of last three or four anal-fin rays. Unbranched anal-fin rays iv(2); branched anal-fin rays 17(9), 18*(10) or 19(2). First branched anal-fin ray longer, remaining rays decreasing in size posteriorly. Anal-fin with distinct anterior lobe, distal profile concave. Anal-fin origin at vertical through dorsal-fin terminus. Anteriormost anal-fin pterygiophore inserted posterior to haemal spine of 14 th (2) vertebrae. Dimorphic males with acute, retrorse hooks on posterior margin and posterior branches of anal-fin rays, posterolaterally arranged on first branched to 3 rd –4 th branched rays. Pectoral-fin rays i*(19), 9*(7), 10(9) or 11(2). Pectoral-fin rays reaching pelvic-fin origin. Pelvic-fin origin anterior to vertical through dorsal-fin origin. Pelvic-fin rays i,7*(19). Pelvic-fin rays with acute bony hooks in males, from unbranched ray to 5 th or 6 th branched ray. Caudal fin forked, with lobes similar in size and rounded tips. Principal caudal-fin rays 19*(18). Twelve (2) dorsal procurrent caudal-fin rays and 9(1) or 10(1) ventral procurrent caudal-fin rays.

Scales cycloid. Longitudinal line 36(1), 37(12) or 38*(8). Pored scales on lateral line 33(1), 36(4), 37(11) or 38*(3); predorsal scale series 4(1), 5(1), 7(1), 8(1), 9(1) or 10*(15); scale rows between lateral line to dorsal-fin origin 4*(21); scale rows between lateral line to pelvic-fin origin 3*(20) or 3.5(1); circumpeduncular scale rows 12*(21). Scales sheath over the base of anterior anal-fin rays 3*(15), 4(5) or 5(1).

Total vertebrae 37 (2). Precaudal vertebrae 14(2), caudal vertebrae 23(2). Supraneurals 4(1) to 5 (1) with narrow bony lamellae on upper portion. Branchiostegal rays 4(2). First gill arch with 2(2) rakers on hypobranchial, 7(2) rakers on ceratobranchial, 1(2) raker on intermediate cartilage, and 3(2) rakers on epibranchial.

Color in alcohol. Overall background body color beige to light yellow ( Fig. 1 ). Guanine pigmentation absent. Large melanophores scattered on dorsal region of head and predorsal region of body. Dark chromatophores aligned along anterior border of nares and dorsal margin of maxilla. Iris with scattered melanophores, more concentrated over distal edges of eye. Presence of longitudinal dark stripe along upper margin of lower jaw. Humeral blotch absent. Oval, darkened area in humeral region due to presence of pseudotympanum. Dark and diffuse subjacent midlateral stripe on posterior region of body, extending between vertical through mid-length of dorsal-fin base to vertical through anal-fin terminus. Dark midlateral stripe more conspicuous from vertical through mid-length of anal-fin base to posterior end. Caudal-peduncle blotch rounded, not reaching dorsal and ventral margins of caudal peduncle, slightly surpassing base of middle caudal-fin rays. Dorsal-fin base with dark patch of pigmentation on its anterior margin. Dorsal fin with concentration of melanophores over first unbranched ray and base of second unbranched ray, forming a small patch of dark pigmentation, more conspicuous in life specimens. Anal-fin base with dark line extending along its length, more intensely pigmented anteriorly. Dark line along ventral margin of caudal peduncle. Dorsal, anal, pectoral, pelvic and caudal fins hyaline, with few scattered melanophores along edge of lepidotrichia. Adipose fin hyaline.

Color in life. Overall dark pigmentation as described above. Body mostly translucent, slightly yellow to brown ( Fig. 2 ). Eye almost totally yellow or brown. Yellow pigmentation more intense on dorsal regions of body and base of caudal-fin lobes. Guanine pigmentation on internal tissue lining opercular apparatus and abdominal cavity. Dark pigmentation on base of dorsal-fin origin. Lateral dark stripe composed by internal pigmentation extending from posterior margin of eye, over dorsal region of opercle, continuous along vertebral column to unpigmented band anterior to caudal peduncle. Caudal peduncle blotch conspicuous. Abdominal region with internal dark pigmentation along dorsal and posterior regions.

Sexual dimorphism. Bony hooks were observed on the anal- and pelvic-fin rays of two males (MZUSP 116046, 21.1-23.5 mm SL). In the anal-fin rays, the hooks were distributed from the last unbranched to the first four branched rays. No other sexual dimorphic feature was observed in the species, including sexual dichromatism in life, as well as no gill-gland on the first branchial arch of males (sensu Oliveira et al., 2012).

Distribution. Microschemobrycon cryptogrammus is so far known only from tributaries of the Rio Curuá, Rio Xingu basin, Pará State, Brazil ( Fig. 3 ).

Etymology. The specific epithet cryptogrammus derives from the Greek words crypto, hidden and grammus, line, alluding the black longitudinal stripes into the body, visible only in live specimens. An adjective.

Habitat and ecological notes. Microschemobrycon cryptogrammus is known from four localities, all being clear water streams with swift current, 2–4 m wide, 1–2 m deep and substrate composed mainly by sand and mud, running through disturbed (pastureland) areas, at altitudes ranging from 234–273 m a.s.l. ( Fig. 4 ). The new species was always captured in low abundance, amid aquatic vegetation. Other Microschemobrycon species are typically found in sandy beaches, living in small shoals ( Lima et al., 2017; Ohara et al., 2017)

Figures

FIGURE 1. Microschemobrycon cryptogrammus, MZUSP 123748, holotype, 23.6 mm SL (A); MZUSP 119647, paratype, 20.4 mm SL (B), both from the tributaries of Rio Curuá drainage, Rio Xingu basin, Pará, Brazil.

FIGURE 2. Coloration in life of Microschemobrycon cryptogrammus, MZUSP 119370, paratype, 19.5 mm SL, igarapé tributary of Rio Curuá (A) and MZUSP 116046, paratype, 23.6 mm SL, tributary of Treze de Maio (B), both from Rio Curuá drainage, Rio Xingu basin, Pará State, Brazil.

FIGURE 3. Map of central region of Brazil showing the geographic distribution of Microschemobrycon cryptogrammus, in the Rio Curuá, Rio Xingu basin, Pará State, Brazil. Type locality = blue dot.

FIGURE 4. Stream inhabited by Microschemobrycon cryptogrammus, type-locality, a tributary of Rio Curuá (A) and a tributary of Rio Treze de Maio (B), both belonging to the Rio Xingu basin, Pará State, Brazil.