Simpsonichthys radiosus, Wilson J. E. M. Costa & Gilberto C. Brasil, 2004

Wilson J. E. M. Costa & Gilberto C. Brasil, 2004, Simpsonichthys radiosus sp. n. (Teleostei: Cyprinodontiformes: Rivulidae): a new annual killifish from the upper Rio Tocantins basin, central Brazil., Zootaxa 737, pp. 1-7 : 2-5

Simpsonichthys radiosus new species

(Figs. 1-2)

Holotype. UFRJ 6017 , male, 23.4 mm SL; Brazil: Estado de Goiás: Formosa, Rio Crixas floodplains, about 6 km from the confluence with Rio Parana (about 15°20’S 47°20’W; altitude about 800 m); G. C. Brasil, 10 May 2004.

Paratypes. UFRJ 6018 , 4 males, 24.3-26.6 mm SL, 5 females, 20.1-23.5 mm SL; UFRJ 6019 , 3 males, 24.8-27.6 mm SL, 3 females, 19.9-22.6 mm SL (c&s); UFRJ 6020 , 5 males, 22.8-26.8 mm SL, 1 female, 22.1 mm SL; UFRJ 6021 , 5 males, 21.9-25.2 mm SL; collected with holotype.

Diagnosis: Distinguished from all congeners by possessing a unique color pattern on the caudal fin in males, consisting of three to five light blue stripes crossing the fin, parallel to fin rays, alternating with subdistal rounded light blue spots (vs. never a similar color pattern). Similar to S. notatus , S. stellatus , S. rufus , S. similis , S. trilineatus , S. auratus , and S. ocellatus , and distinguished from all other species of the genus by having the frontal squamation A-patterned (vs. E-patterned); differs from these species in having a broad basihyal (width about 85% of basihyal length, vs. 50-75%).

Description: Morphometric data given in Table 1. Male larger than female, largest male 27.6 mm SL. Dorsal profile convex from snout to end of dorsal-fin base, approximately straight on caudal peduncle. Ventral profile convex from lower jaw to end of analfin base, nearly straight on caudal peduncle. Body moderately deep, compressed, depth about 1.2 times body width in larger males. Greatest body depth at level of pelvic-fin base. Caudal peduncle short, about two thirds length of head.

Tip of dorsal fin slightly pointed, tip of anal fin slightly pointed in male, rounded in female. Tip of dorsal and anal fins of male with rudimentary filamentous rays. Median dorsal-fin rays branched, anterior and posterior rays unbranched. Caudal fin subtruncate. Pectoral fin elliptical. Posterior margin of pectoral fin reaching vertical between base of 1st and 3rd anal-fin rays in male, between anus and urogenital papilla in female. Tip of pelvic fin reaching base of 2nd or 3rd anal-fin ray in male, between urogenital papilla and base of 1st anal-fin ray in female. Pelvic-fin bases in close proximity. Dorsal-fin origin anterior to anal-fin origin; anal-fin origin on vertical between base of 4th and 6th dorsalfin rays in male, between base of 1st and 3rd dorsal-fin rays in female; dorsal and anal-fin origins between neural spines of 7th and 8th vertebrae in male, 9th and 10th vertebrae in female. Dorsal-fin rays 23-26 in male, 17-19 in female; anal-fin rays 21-23 in male, 18- 22 in female; caudal-fin rays 25-26; pectoral-fin rays 12-13; pelvic-fin rays 5-6.

Scales large, cycloid. Body and head entirely scaled, except on ventral surface of head. Anal-fin base without scales. Frontal squamation A-patterned. Longitudinal series of scales 25-27; transverse series of scales 10; scale rows around caudal peduncle 12. One minute ctenii-like contact organ on each scale of anteroventral portion of flank of male. Small papillate contact organs on dorsal surface of dorsalmost pectoral-fin ray of male. Supraorbital neuromasts 11-13, arranged in continuous series.

Basihyal triangular, longest width about 85 % of length; basihyal cartilage about 30 % of total length of basihyal. Six branchiostegal rays. Three teeth on second pharyngobranchial. Gill-rakers on first branchial arch 3 + 9. Vomerine teeth absent. Dermosphenotic absent. Total vertebrae 27-28.

Coloration: Male: Side of body light purplish brown to reddish brown on anteroventral portion, with 8-9 gray bars, and few pale blue dots irregularly arranged on dorsal portion; black rounded blotch on lateral midline, overlapping third bar, at vertical through dorsal-fin origin. Opercular region golden, with light blue spots. Iris light yellow, with dark brown bar. Dorsal fin reddish brown with subbasal row of light blue spots, and similar slightly smaller spots on posterior region; distal bright blue stripe with black dorsal outline. Anal fin reddish brown, with five faint gray bars. Caudal fin dark reddish brown with 3-5 light blue stripes parallel to fin rays, alternating with subdistal rounded light blue spots. Pectoral fin hyaline. Pelvic fin reddish brown, tip dark gray.

Female: Side of body light purple, with small dark gray spots; spot on anterocentral portion of flank black. Opercular region light golden with gray dots. Iris light yellow, with dark gray bar. Unpaired fins hyaline with small gray spots on basal portion; small light blue spot on posterior portion of anal fin. Paired fins hyaline.

Distribution: Known only from the type locality, floodplains of Rio Crixás, Rio Paranã drainage, upper Rio Tocantins basin, central Brazil.

Etymology: From the Latin radiosus (that emits light rays), an allusion to the unique color pattern of caudal fin in males.