Characidium mirim, Netto-Ferreira, André L., Birindelli, José L. O. & Buckup, Paulo A., 2013

Netto-Ferreira, André L., Birindelli, José L. O. & Buckup, Paulo A., 2013, A new miniature species of Characidium Reinhardt (Ostariophysi: Characiformes: Crenuchidae) from the headwaters of the rio Araguaia, Brazil, Zootaxa 3664 (3), pp. 361-368 : 362-365

Characidium mirim , new species

Figure 1 , Table 1

Holotype. MZUSP 111123 (ex-MZUSP 101393), 20.2 mm SL. Brazil, Mato Grosso, rio das Mortes, at bridge on road between Chapada dos Guimarães and Campo Verde, 15°30’20”S 55°13’38”W, 25 Jan 2009, A. L. Netto- Ferreira, J. L. O. Birindelli, L. M. Sousa, P. Hollanda-Carvalho.

Paratypes. (11 specimens). All from Mato Grosso, Brazil: MZUSP 101393 (2, 18.3-18.6 mm SL), collected with holotype; 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 CS, 23.4 mm SL), small stream near Santo Antônio do Leste, 14°52’30”S 54°5’0”W, 18 Jan 2002, N. A. Menezes, O. T. Oyakawa, G. Guazzelli, R. Quevedo; MZUSP 97724 (4, 18.9-19.7 mm SL), Vereda de Buriti, at BR-070, between Campo Verde and Primavera do Leste, 15°34’9”S 54°33’21”W, 17 Jan 2002, N. A. Menezes, O. T. Oyakawa, G. Guazzelli, R. Quevedo.

Diagnosis. Characidium mirim is distinguished from all congeners, except Characidium bahiensis , C. interruptum , C. nupelia , C. rachovii , C. stigmosum , and C. xavante by having an incomplete lateral line with 5–7 perforated scales (vs. lateral line with more than 15 perforated scales). The new species is further distinguished from all congeners, except C. nupelia , C. stigmosum C. vestigipinne , and C. xavante by lacking an adipose fin. Characidium mirim is distinguished from Characidium nupelia and C. xavante by having a conspicuous dark midlateral stripe (vs. midlateral stripe absent or represented by a thin and inconspicuous dark line), nine to 11 dark transverse bars on the dorsum not extending ventrally onto side of body ( Fig. 1 b; vs. 12 to 18 dark transverse bars on dorsum and side of body) and lacking a dark blotch on the caudal peduncle (vs. dark blotch present). Characidium mirim is further distinguished from C. xavante by having 12 series of scales around the caudal peduncle (vs. 10). Characidium mirim is distinguished from C. stigmosum by having a conspicuous dark midlateral stripe (vs. stripe absent), the side of body without dark blotches (vs. dark blotches present), the fins hyaline (vs. generally dark), and 12 circumpeduncular scales (vs. 14). The new species differs from C. vestigipinne by the absence of blotches on pelvic and anal fins (vs. blotches present).

Holotype Range Mean N SD Description. Morphometric data summarized in Table 1 . Body laterally compressed. Dorsal profile convex between anterior tip of premaxilla and vertical through posterior margin of orbit, concave from that point to vertical through pectoral-fin origin, then convex from latter point to end of dorsal-fin base; nearly straight or slightly concave between dorsal and caudal-fin bases. Ventral profile convex between tip of lower jaw and terminus of anal-fin (somewhat more arched in mature females). Greatest body depth at dorsal fin origin.

Snout narrow in dorsal view, short and blunt in lateral view. Mouth small, subterminal. Maxilla not reaching vertical through anterior margin of orbit. Orbit circular, diameter distinctly greater than snout length. Cheek depth about half of orbit diameter. Nares separated; posterior naris considerably closer to eye than to anterior; margin of anterior naris expanded, forming circular rim. Dermal flaps absent on anterior and posterior nares. Dorsal cranial fontanel reduced, bordered by posterior portion of parietals and supraoccipital. Branchiostegal rays 5; 4 attached to anterior ceratohyal.

Teeth conical. Premaxilla with single row of 6 teeth gradually decreasing in size posteriorly. Maxilla edentulous. Dentary with single row of 12 teeth gradually decreasing in size posteriorly. Single row of 3 teeth on ectopterygoid. Mesopterygoid edentulous. Scales cycloid; parallel radii present on posterior region of scales. Axillary scale absent. Lateral line incomplete, with 5(3), 6*(8) or 7(4) perforated scales; lateral series of scales 28 (1), 29 (8), 30*(6). Series of scales between lateral line and dorsal-fin origin 4*(14). Series of scales between lateral line and pelvic-fin origin 3 (3) or 4* (11). Circumpeduncular scales 12*(15). Predorsal scales 9 (4), 10*(6), 11 (1). Isthmus completely covered with scales.

Dorsal-fin rays iii,11* (9) or iv,10 (6); pectoral-fin rays ix,2*(1), ix(3), x(10) or xi(1); pelvic-fin rays i,7* (14) or i,8 (1); anal-fin rays iii,6 (14) or iii,7* (16); caudal-fin rays i,6,7,i (1), i,7,7,i* (11), i,7,8,i (1). Distal portion of dorsal and anal fins slightly rounded. Pectoral and pelvic fin margins rounded. Caudal fin forked, with lobes rounded. Adipose fin absent.

Total vertebrae 31. Supraneural bones between neural spine of sixth centrum and anterior dorsal-fin pterygiophore eight.

Color in alcohol. Ground color tan, slightly countershaded. Head with dark stripe from snout tip to posterior margin of dorsal portion of opercle and with dark transverse bar on dorsum of posterior portion of head. Body with dark midlateral stripe from dorsal portion of opercular opening to posterior of caudal peduncle, and 9 to 12 dark transverse bars on dorsum; four situated anterior to dorsal-fin origin, two under dorsal-fin base, and four between dorsal-fin terminus and origin of caudal-fin rays. Dark caudal spot inconspicuously present on base on median caudal-fin rays. Fins mostly hyaline. Dorsal fin with inconspicuous dark band on median portion of rays and intervening membranes.

Sexual dimorphism. Adult males with bony hooks on distal portions of pectoral- and pelvic-fin rays; anal fin distinctly enlarged, with rounded distal profile ( Fig. 1 a); dark transverse bars on dorsum distinctly less intense ( Fig. 1 a) than in females ( Fig. 1 b).

Distribution. Characidium mirim is known from the upper portion of the rio das Mortes and its tributaries, in the Planalto do rio das Mortes, Mato Grosso, Brazil ( Fig. 2 ).

Etymology. The specific epithet mirim comes from the Tupi, meaning small, and is given in reference to the minute size of the new species, which represents the smallest known species of Characidium . A noun in apposition.

Figures

FIGURE 1. Characidium mirim, (a) holotype, MZUSP 111123, 20.2 mm SL, male; (b) paratype, MZUSP 101393, 18.6 mm SL, female; both from rio das Mortes, 15 ° 30 ’ 20 ” S 55 ° 13 ’ 38 ” W.

FIGURE 2. Distribution of Characidium mirim. White circle indicates the type locality.

Tables

TABLE 1. Morphometric data of Characidium mirim. SD = Standard Deviation.

Total length (mm) 25.7	21.9 – 25.7 23.5	12
Standard length (mm) 20.2	16.6 – 20.2 18.6	15
Head length (mm) 5.7	4.4 – 5.7 5.0	15
Percentage of SL
Body depth at dorsal-fin origin 29.5	26.5 – 31.5 29.2	15 1.5
Body depth at anal-fin origin 21.4	17.0 – 21.4 19.4	15 1.1
Body depth at caudal peduncle 13.2	10.8 – 13.2 12.0	15 0.7
Head length 28.1	24.9 – 28.8 26.8	15 1.2
Caudal peduncle length 18.9	18.5 – 23.6 20.6	15 1.3
Preanal distance 72.4	68.3 – 73.3 70.6	15 1.7
Predorsal distance 50.4	47.6 – 51.4 49.7	15 1.1
Prepectoral distance 30.9	26.5 – 31.2 29.2	15 1.4
Prepelvic distance 52.7	50.4 – 55.2 52.6	15 1.4
Anal-apex distance 94.7	87.0 – 97.0 91.4	15 2.5
Body width 13.2	9.4 – 13.2 11.5	15 1.0
Percentage of HL
Snout length 25.18	17.1 - 25.6 21.5	15 2.1
Orbital diameter 32.0	32.0 - 39.3 35.8	15 2.3
Cheek depth 18.3	14.2 - 19.7 16.6	15 1.6
Anterior naris–orbit 9.7	7.1 - 9.68 8.4	15 0.9
Posterior naris–orbit 3.5	2.0 - 4.00 2.8	15 0.5
Snout–maxillary tip 28.9	22.2 - 28.8 25.0	15 1.9
Interorbital distance 27.8	21.5 - 27.8 24.7	15 1.7