Rivulus litteratus, Costa, 2005

Costa, Wilson J. E. M., 2005, Seven new species of the killifish genus Rivulus (Cyprinodontiformes: Rivulidae) from the Paraná, Paraguay and upper Araguaia river basins, central Brazil, Neotropical Ichthyology 3 (1), pp. 69-82 : 75-77

Rivulus litteratus , new species

Figs. 6-7

Rivulus sp. - Lacerda, 1989: 25 (Ponte Branca, rio Araguaia, central Brazil).

Rivulus pictus (non Costa, 1989). - Costa et al., 2003: 143 (misidentification of specimens from Alto Araguaia).

Holotype. UFRJ 5956, male, 26.9 mm SL; Brazil: Estado de Mato Grosso: Município de Alto Araguaia, córrego do Sapo, upper rio Araguaia basin, road MT-100, 31 km S of Alto Araguaia, 17º33’38.5”S 53º18’33.1”W, altitude 750 m; W. J. E. M. Costa, B. B. Costa and C. P. Bove, 14 Jan 2004.

Paratypes. Brazil: Estado de Mato Grosso: Município de Alto Araguaia, upper rio Araguaia basin: UFRJ 5957; 3 males, 23.4-28.1 mm SL, 4 females, 16.5-27.4 mm SL; collected with the holotype. UFRJ 5837, 12 males, 18.8-24.1 mm SL, 28 females, 14.2-24.3 mm SL, 1 juvenile, 12.4 mm SL; MCP 36123, 4 males, 19.1-20.2 mm SL, 6 females, 20.1-21.8 mm SL; UFRJ 5958, 3 males, 22.2-23.8 mm SL, 3 females, 22.3-23.9 mm SL (c&s); same locality; W. J. E. M. Costa, S. M. Q. Lima, D. F. Belote and E. S. Araújo, 6 Apr 2002 . - MZUSP 73303 , 6 males, 23.5-26.6 mm SL, 9 females, 24.8- 30.2 mm SL; córrego Tapera, km 482.37 of the Ferronorte railway, 17 o 22’18”S 53 o 14’25”W; C. L. R. Moreira and F. C. T. Lima, 18 May 2001 .

Diagnosis. Distinguished from all other species of the R. punctatus group by the unique color pattern on the flank in males, with red marks variable in shape, highly overlapped (vs. never a similar color pattern), and caudal fin with dark gray stripe posterior to caudal spot in females (vs. stripe absent). Also distinguished from all other members of the R. punctatus group by the combination of the following features: frontal squamation F-patterned (vs. Epatterned), flank with striking iridescent colors in male, contrasting metallic blue to greenish blue on middle of flank with light purplish blue above anal fin and brownish golden on anterior dorsolateral portion of body (vs. never a similar color pattern), no distinctive dark stripe along midline of flank (vs. stripe present); red bars on caudal fin in males (vs. bars absent).

Description. Morphometric data in Table 4. Largest specimen 30.2 mm SL, female. Dorsal profile slightly convex from snout to end of dorsal-fin base, approximately straight on caudal peduncle. Ventral profile convex on head, almost straight from anterior portion of venter to end of anal-fin base, nearly straight to slightly concave along caudal peduncle. Body slender, subcylindrical anteriorly, slightly deeper than wide, to compressed posteriorly. Greatest body depth at level of pelvic-fin base.

Dorsal and anal fins gently pointed in male, rounded in female. Caudal fin almost circular. Pectoral fin rounded, posterior margin on vertical anterior to pelvic-fin base. Tip of pelvic fin reaching base of first or second anal-fin ray in male, and vertical anterior to anus in female. Pelvic-fin bases in close proximity. Dorsal-fin origin on vertical through base of 7th or 8th anal-fin ray, and between neural spines of 18th and 19th vertebrae. Anal-fin origin between pleural ribs of 13th and 15th vertebrae. Dorsal-fin rays 9-10; anal-fin rays 13-14; caudal-fin rays 31-33; pectoral-fin rays 13; pelvic- fin rays 7.

Scales large, cycloid. Trunk scaled; head scaled except on its anteroventral surface. Body scales slightly extending over caudal-fin base; no scales on dorsal and anal fins. Frontal squamation F-patterned; E-scales not overlapping medially; scales arranged in circular pattern around central Ascale without exposed margins. Longitudinal series of scales 31-32; transverse series of scales 8; scale rows around caudal peduncle 16. Contact organs absent. Supraorbital neuromasts 3 + 3. Six branchiostegal rays. Gill rakers of first branchial arch 1 + 7-8. Three or four vomerine teeth. Total vertebrae 29-30.

Coloration. Male: Side of body metallic green, purplish blue above anal fin, with overlapped red marks of variable shapes, including chevron-like oblique bars with anteriorly directed vertex, horizontal rows of spots, and narrow and short zigzag stripes; sometimes, midlateral dark greenish gray zone, between humeral region and vertical through dorsal fin origin, when exposed to light. Anterior dorsolateral portion of flank greenish golden. Dorsum light yellowish brown with faint brown spots, venter white. Opercular region golden with two oblique dark red bars. Red marks on opercle and humeral region becoming dark reddish brown when exposed to light. Infraorbital region and ventral surface of head white. Lower jaw reddish gray. Iris light yellow. Dorsal fin yellow with four or five narrow red bars. Anal fin light yellow, base blue with five short red bars. Caudal fin yellow with five to seven red bars crossing fin except on ventral portion. Pelvic fin pale yellow. Pectoral fin hyaline.

Female: Side of body pale metallic green, purplish blue above anal fin, with narrow, coalesced red chevron-like oblique bars with anteriorly directed vertex; brown blotch on humeral region. Anterior dorsolateral portion of flank pale greenish golden. Dorsum light yellowish brown with brown dots, venter white. Opercular region pale golden with two oblique brown bars. Brown marks on opercle and humeral region becoming darker when exposed to light. Infraorbital region and ventral surface of head white. Lower jaw reddish gray. Iris light yellow. Dorsal fin yellow with four dark gray bars; broad dark gray to black distal stripe. Anal fin light yellow, base blue with five short red bars; broad dark gray to black distal stripe. Caudal fin light yellow with four or five dark gray bars; sometimes parts of some bars broken forming elongate spots; black spot on subdorsal portion of caudal fin base; dark gray stripe posterior to black spot, sometimes inconspicuous; caudal fin margins black. Pelvic fin pale yellow, anterior margin dark gray to black. Pectoral fin yellowish hyaline.

Distribution. Upper rio Araguaia basin, central Brazil ( Fig. 2 ).

Etymology. From the Latin litteratus (marked with letters), an allusion to the color pattern of the males, comprising red marks on the flank resembling letters.

Figures

Fig. 6. Rivulus litteratus, UFRJ 5956, male, holotype, 26.9 mm SL (one day after collection); Brazil: Mato Grosso: Alto Araguaia. Photo by W. J. E. M. Costa.

Fig. 7. Rivulus litteratus, UFRJ 5957, female, paratype, 25.6 mm SL (one day after collection); Brazil: Mato Grosso:Alto Araguaia. Photo by W. J. E. M. Costa.

Fig. 2. Geographic distribution of species of the genus Rivulus in the Paraná, Paraguay, and upper Araguaia river basins, central Brazil.