Characidium nana, Mendonça, Marina B. & Netto-Ferreira, Andre L., 2015

Mendonça, Marina B. & Netto-Ferreira, Andre L., 2015, New species of Characidium (Characiformes: Crenuchidae) from the Rio Tapajós and Rio Xingu drainages, Pará, Brazil, Zootaxa 4021 (1), pp. 187-194 : 188-192

Characidium nana , new species

( Fig. 1 )

Holotype. MPEG 31838, 21.5 mm SL, Brazil, Pará, Rio 13 de Maio, approximately 40 km from Castelo dos Sonhos, 8°38'54.65"S 55°1'45.04"W, 14 Aug 2012, M. B. Mendonça.

Paratypes. All collected with holotype. INPA 48536, 3, 16.4–17.3 mm SL; MNRJ 43743, 3, 15.3–18.3 mm SL; MPEG 25792, 10, 14.0– 16.7 mm SL; 5 c&s, 15.7–17.1 mm SL; MZUSP 117154, 3, 16.7–21.3 mm SL.

Non-type material. MPEG 7844, 1, 19.4 mm SL, Brazil, Pará, Altamira, Rio Parazinho, tributary of lower Rio Xingu, 8°31’17”S 55°06’31”W, 0 8 Jun 2002, M. Camargo & T. Giarrizzo; MPEG 7853, 5, 12.1–25.3 mm SL Brazil, Pará, Rurópolis, Igarapé Negro, tributary of lower Rio Tapajós, at the BR-163 road, 4°12'27"S 55°31'39"W, 14 Jun 2002, M. Camargo & T. Giarrizzo.

Diagnosis. Characidium nana is distinguished from all congeners, except C. bahiense , C. interruptum , C. laterale , C. mirim , C. nupelia , C. rachovii , C. stigmosum and C. xavante by the short, incomplete lateral line, the absence of the inner dentary series of teeth, and the absence of the parietal branch of the supraorbital laterosensory canal. The new species is distinguished from C. bahiense , C. interruptum , C. laterale and C. rachvoii by the lack of the adipose fin (vs. adipose fin present); from Characidium mirim and C. stigmosum by the presence of a conspicuous dark blotch onto the caudal peduncle (vs. caudal blotch absent); and from C. nupelia and C. xavante by the presence of a broad, conspicuous dark midlateral stripe (vs. narrow, inconspicuous midlateral stripe). Characidium nana can be further distinguished from C. xavante by the presence of 12 circumpeduncular scales (vs. 10).

Description. Morphometric data summarized in Table 1 . Body compressed, greatest body depth at dorsal fin origin. In dorsal view, snout convex and robust; body width increasing from posterior margin of orbit to end of opercle, becoming narrower from that point to caudal-fin insertion. Dorsal profile nearly straight from tip of snout to posterior margin of posterior nostril, convex from that point to first pre-dorsal scale, slightly convex from that point to dorsal-fin terminus, concave, nearly straight, from that point to caudal-fin insertion. Ventral profile convex between tip of lower jaw and pectoral-fin insertion, straight to slightly convex from that point to pelvic-fin insertion, moderately ascending from the latter point to last anal-fin ray, concave from that point to caudal-fin insertion.

Mouth small, terminal. Maxilla reaching vertical through anterior margin of orbit. Premaxilla with single row of 6 (2), 7 (2) or 8 (1) conical teeth gradually decreasing in size laterally. Maxilla edentulous. Dentary with single row of 8 (3) or 9 (2) conical teeth gradually decreasing in size posteriorly. Single row of 4 (1), 6 (1) or 7 (3) ectopterygoid teeth. Mesopterygoid edentulous. Nostrils separated by fleshy bridge, without dermal flaps; posterior nostril circular, closer to eye than to anterior nostril; anterior nostril smaller than posterior. Dorsal cranial fontanel reduced, bordered by posterior portion of parietals and supraoccipital. Branchiostegal rays 4 (5); 3 attached to anterior ceratohyal (5), and 1 attached to posterior ceratohyal (5).

Scales cycloid, with usually three radii originating at same point on anterior margin of scale, and at least two radii originating at second third of scale, lying dorsally and ventrally to central bundle of radii; all reaching posterior border of scale. Lateral line longitudinal series with 30 (1), 31 (3), 32* (7), 33 (6), 34 (4), or 35 (1) scales, of which 5 (4), 6 (9), 7 (10), 8 (1), or 9* (1) are perforated. Circumpeduncular scales 12* (23). Four series of scales above and below lateral line. Scales in pre-dorsal series 8 (1) or 9* (23). Isthmus completely scaled. Pelvic-fin axillary scale present.

Pectoral-fin rays iii,5 (1), ii,6* (18), or ii,7 (6); lateralmost ray originating at vertical through second lateral line scale; tip of pectoral fin surpassing basipterygium when adpressed to body, but not reaching pelvic-fin insertion; third and fourth rays longest. Pelvic-fin rays i,8* (24), or ii,8 (1); lateralmost pelvic-fin ray originating at vertical opposition between third and fourth dorsal-fin ray; second and third rays longest, with their tips reaching anal-fin insertion. Supraneurals 4 (5) anterior to neural spine of centra 5 to 8. Dorsal-fin rays ii,9* (20), iii,9 (3), i,10 (1), ii,10 (1); origin at vertical through of 11th scale of lateral series; when adpressed against body, tip reaching vertical through anal-fin insertion; fourth and fifth rays longest; first pterygiophore posterior to neural spine of centrum 9 (2) or 10 (3). Adipose fin absent. Anal-fin rays i,7 (1), i,8* (1), ii,6 (4), ii,7 (9), or ii,8 (10); fifth and sixth rays longest; first pterygiophore inserted posterior to haemal spine of centrum 20. Caudal-fin rays i,9/8,i (25). Distal portion of all fins slightly rounded; caudal fin forked, with rounded, similar in length lobes. Precaudal vertebrae 18 (2) or 19 (3), caudal vertebrae 13 (3) or 14 (2), total vertebrae 32 (3) or 33 (2).

Color in alcohol. Background color of head and body pale yellow. Disperse chromatophores on mid-dorsal area of head, and anterior and posterior margins of orbit. Concentration of chromatophores on upper lip, and area between nostrils, forming clear v- or y-shaped pattern. Sides of head gradually lighter ventrally, except on longitudinal stripe. Longitudinal stripe extending from tip of snout to posterior margin of opercle. Opercular membrane hyaline. Midlateral longitudinal stripe extending onto body from rear of head to base of median caudalfin rays overlapping caudal blotch, except in five specimens smaller than 16.7 mm SL in which longitudinal stripe only reaches near caudal blotch; stripe depth ranging from one to two scales. Sides of body with few, scattered chromatophores ventral to longitudinal stripe. Humeral blotch absent, or overlapped by longitudinal stripe. Vertical bars on sides of body 9 (1), 10 (2), 11 (7), 12 (6), 13 (2), 14 (3) or 15* (4); bars anterior to dorsal-fin origin 3 (1), 4 (5), 5 (14) or 6* (3); bars along dorsal-fin base 1 (13), 2* (9) or 4 (1); and bars between dorsal-fin terminus and distal tip of caudal peduncle 4 (2), 5 (11), 6* (7), 7 (2) or 8 (1). Ventral tip of vertical bars usually not reaching longitudinal stripe, except those posterior to anal-fin origin, rarely reaching ventral portion of body. In ventral view, dark stripe originating at insertion of medialmost pelvic-fin ray, extending to anal fin, rarely reaching 5th analfin ray. Dark, conspicuous caudal blotch present at distal portion of caudal peduncle, extending onto base of median caudal-fin rays. Pectoral, pelvic and anal fins mostly hyaline, with rays bordered internally by few chromatophores. Dorsal fin with inconspicuous dark band on median portion of rays and intervening membranes. Caudal fin with vertical bar at base of largest procurrent and principal rays.

Sexual dimorphism. No secondary sexual characters were observed in specimens of Characidium nana .

Distribution. Characidium nana is known from the Rio 13 de Maio, in the Rio Curuá, at Serra do Cachimbo, and the Rio Parazinho, both in the Rio Xingu drainage, and from Igarapé Negro, in the Rio Tapajós drainage ( Fig. 2 ).

Etymology. Named in honor of Mariana Barreira Mendonça, the first author’s sister, known by her family and friends as “ Naná ”. Treated as a noun in apposition.

Remarks. Characidium nana shares with its congeners the presence of a basicaudal dot described by Buckup (1993a) as the sole synapomorphy for the genus Characidium . The species described herein presents two of the three diagnostic characters defining the C4 clade: the absence of the inner series of dentary teeth and the absence of the parietal branch of the supraorbital laterosensory canal. However, it has a polymorphic condition on the number of vertical bars on the body, where Characidium nana has 9–15 vertical bars, fitting both character states described by Buckup (1993a) and Netto-Ferreira et al. (2013) (less than 12 vs. more than 12 vertical bars). The phylogenetic analysis ( Fig. 3 ) yielded a single tree (13 steps) resulting in Characidium nana as the sister species of a clade comprising C. nupelia , C. xavante , C. mirim , C. stigmosum , C. rachovii , C. occidentale , C. orientale and C. vestigipinne . The clade is supported by the absence of the adipose fin (reversed in C. rachovii , C. occidentale , C.

orientale and C. vestigipinne ), and the group itself is included in a unresolved clade with C. bahiense , C. interruptum , C. laterale supported by the reduced lateral line (secondarily reversed in C. occidentale , C. orientale and C. vestigipinne ), as the sister group of C. lanei and C. lagossantense .

Comparative material examined. All from Brazil. Characidium bahiense . Bahia State. MZUSP 40224, 2, 19.3–20.4 mm SL, Rio Icatu. Characidium hasemani . Pará State. MPEG 4568, 10, 35.5–41.2 mm SL, Rio Itacaiúnas. Characidium interruptum . Rio de Janeiro State. MZUSP 49152, 4, 16.9–20.6 mm SL, Rio Jundiá. Characidium lagosantense . São Paulo State. MZUSP 100779, 3, 23.2–31.4 mm SL, Rio Corumbataí. Characidium laterale . Mato Grosso State. MZUSP 96659, 5, 18.5–23.8 mm SL. Characidium mirim . Mato Grosso State. ANSP 193193, 1, 18.6 mm SL, MNRJ 40135, 4, 17.6–19.1 mm SL, MZUSP 97705, 2, 16.6–19.1 mm SL, 1 c&s, 23.4 mm SL, Igarapé near Stanto Antonio do Leste; MZUSP 97724, 4, 18.9–19.7 mm SL, Vereda Buriti, between Campo Verde and Primavera do Leste; MZUSP 111123, holotype, 20.2 mm SL, MZUSP 101393, 2, 18.3–18.6 mm SL, Rio das Mortes. Characidium rachovii . Rio Grande do Sul State. MZUSP 49165, 5, 26.3–32.6 mm SL, Arroio Bolacha. Characidium steindachneri . Guyana. ROM 86008, 7, 31–39 mm SL, Rupununi river. Characidium xavante . Mato Grosso State. MZUSP 91774, 2, 17–20.4 mm SL, tributary of Rio Culuene.

Figures

FIGURE 1. Characidium nana, holotype, MPEG 31838, 21.5 mm SL, from Rio 13 de Maio, approximately 40 km from Castelo dos Sonhos, Pará, Brazil.

FIGURE 2. Map of Rio Tapajós and Rio Xingu, and adjoining areas, showing distribution of Characidium nana. White circle indicates the type locality.

FIGURE 3. Single most parsimonious tree (13 steps – CI 0.69; RI 0.87) obtained from the analysis of a modified version of the data matrix from Netto-Ferreira et al. (2013), with the inclusion of Characidium hasemani and C. steindachneri as additional outgroups, and the new species C. nana. Zero length branches are collapsed.

Tables

TABLE 1. Morphometrics of Characidium nana. SD = Standart Deviation.

	Holotype	Range	Mean	N	SD
Total length (mm)	26.5	17.9 – 27.3	21.0	23
Standard length (mm)	21.5	14.0 – 21.5	16.7	25
Head length (mm)	5.6	4.1 – 5.8	4.6	25
Percentage of SL
Body depth at dorsal-fin origin	24.8	20.6 – 25.1	22.9	25	1.4
Body depth at anal-fin origin	16.2	12.9 – 16.2	15.0	24	1.0
Body depth at caudal peduncle	10.2	8.5 – 11.1	10.2	25	0.7
Head length	25.9	25.9 – 29.4	27.8	25	0.8
Caudal peduncle length	17.3	16.3 – 21.7	19.3	25	1.3
Preanal distance	71.4	71.3 – 76.4	73.2	25	1.4
Predorsal distance	47.5	47.5 – 51.1	49.0	25	0.8
Prepectoral distance	26.7	26.3 – 30.5	28.2	25	1.1
Prepelvic distance	47.9	47.4 – 52.7	50.4	25	1.5
Anal-apex distance	87.9	87.9 – 92.5	89.8	24	1.4
Body width	10.2	9.1 – 11.6	10.4	25	0.8
Percentage of HL
Snout length	20.8	19.0 – 23.1	20.6	25	1.1
Orbital diameter	36.4	36.4 – 42.1	38.6	25	1.7
Cheek depth	8.1	7.5 – 12.0	9.7	25	1.3
Anterior naris–orbit	9.7	6.2 – 9.8	8.4	25	1.0
Posterior naris–orbit	3.1	2.2 – 4.4	3.3	25	0.6
Snout–maxillary tip	21.9	20.5 – 24.7	22.4	25	1.2
Interorbital distance	28.4	26.3 – 31.3	28.8	25	1.4