Simpsonichthys nielseni, Wilson J. E. M. Costa, 2005

Wilson J. E. M. Costa, 2005, Simpsonichthys nielseni sp. n. (Teleostei: Cyprinodontiformes: Rivulidae): a new annual killifish from the São Francisco River basin, Brazil., Zootaxa 1039, pp. 57-64 : 58-63

Simpsonichthys nielseni new species

(Figs. 1-2)

Simpsonichthys sp. (Costa, in press).

Holotype. UFRJ 6060, male, 37.0 mm SL; Brazil: Estado de Minas Gerais, temporary pool in Pirapora, São Francisco River floodplains, 17°21’59.6”S 44°56’32.3”W, altitude 500 m; W. J. E. M. Costa & C. P. Bove, 22 January 2005.

Paratypes. UFRJ 6061, 3 males, 36.3-40.5 mm SL, 4 females, 29.1-31.1 mm SL ; UFRJ 6062, 1 male, 32.8 mm SL, 4 females, 29.8-30.7 mm SL (c&s) ; MCP 37306, 1 male, 37.2 mm SL, 1 female, 30.9 mm SL; all collected with holotype .

Diagnosis: Distinguished from all congeners in having six or seven light greenish yellow stripes on the caudal fin in males. Similar to S. stellatus and distinguished from all other species of the S. notatus group by possessing a row of elongated light spots alternating with black interspaces on the basal portion of the dorsal fin in males (vs. never a similar color pattern). Differs from S. stellatus in having caudal fin greenish yellow in males (vs. dark brownish red) and by the absence of a dark gray to black distal stripe on the anal fin in males (vs. presence).

Description: Morphometric data appear in Table 1. Males larger than females, the largest male examined 40.5 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 anal-fin base, nearly straight on caudal peduncle. Body moderately deep, compressed, depth about 1.8 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 pointed. Tip of anal fin pointed in males, rounded in females. Short filamentous rays on tips of dorsal and anal fins in males, tip of filaments reaching vertical through caudal-fin base. Anterior and posterior rays of dorsal-fin rays, including rays on tip of fin, unbranched; the median rays branched. Caudal fin subtruncate in males, rounded in females. Pectoral fin elliptical. Posterior margin of pectoral fin reaching vertical between base of 4th and 6th anal-fins ray in males, through pelvic-fin base in females. Tip of pelvic fin reaching between base of 3rd and 4th anal-fin rays in males, between urogenital papilla and base of 1st anal-fin ray in females. Pelvic-fin bases medially in contact. Dorsal-fin origin anterior to anal-fin origin in males, anal-fin origin on vertical between base of 2nd and 4th dorsal-fin rays; dorsal-fin origin slightly anterior to slightly posterior to anal-fin origin in females. Dorsal-fin origin between neural spines of vertebrae 8 and 9 in males, between neural spines of vertebrae 9 and 11 in females. Anal-fin origin between pleural ribs of vertebrae 8 and 9 in males, between pleural ribs of vertebrae 9 and 11 in females. Dorsal-fin rays 21-22 in males, 16-17 in females; anal-fin rays 19-21 in males, 17-18 in females; caudal-fin rays 25-27; pectoral-fin rays 12-13; pelvic-fin rays 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 26-27; transverse series of scales 9-10; scale rows around caudal peduncle 12-13. Minute contact organ on each scale of anteroventral portion of flank in males. Small papillate contact organs on upper surface of dorsal-most ray of pectoral-fin in males. Supraorbital neuromasts 11-12, arranged in a continuous series.

Supraoccipital process short, reaching vertical through posterior portion of neurocranium. Basihyal triangular, longest width about 60 % of length; basihyal cartilage about 35 % of total length of basihyal. Six branchiostegal rays. Three teeth on second pharyngobranchial. Gill-rakers on first branchial arch 2 + 10. Vomerine teeth absent. Dermosphenotic absent. Ventral process of posttemporal long. Total vertebrae 27.

Coloration: Males: Side of body dark yellow ochre, with 9-11 dark purplish gray bars and light blue dots; venter yellowish white. Side of head yellow ochre to bright greenish blue on opercular and infraorbital region. Scales on posterodorsal side of head and anterodorsal portion of flank red. Iris light purplish yellow, with dark brown bar through center of eye. Dorsal fin greenish brown; 7-8 greenish yellow elongate spots forming short bars on basal region, alternating with dark gray to black elongate spots; row of greenish blue short lines along distal margin of fin. Anal fin greenish brown, with 6 light greenish yellow bars. Caudal fin greenish yellow, with greenish blue margin; 6-7 light greenish yellow stripes, parallel to fin rays, radially diverging from fin base to fin margin, each stripe distally terminating in sharp tip, and alternating with elongate spots of identical color on subdistal portion of fin. Pelvic fin purplish brown. Pectoral fin hyaline.

Females: Side of body light yellowish brown, with dark gray spots; spots above analfin base sometimes elongate, forming short bars; 2-3 spots on anterocentral portion of flank black; venter pale golden. Opercular region greenish golden. Iris light yellow, with gray bar through center of eye. Unpaired fins hyaline with black small spots on basal region; small light blue spot on posterior margin of anal fin, just posterior to fin base. Paired fins hyaline.

Distribution: Known only from the type locality, the floodplains of the middle São Francisco River floodplains, Pirapora, Estado de Minas Gerais, Brazil.

Habitat: The new species was found in a temporary pool in the Cerrado, a typical savannah-like vegetation from central Brazil. The pool was shallow, about 1 m deep, densely covered by aquatic vegetation (Figs. 3-4). The water was dark gray, slightly turbid, and the pH 7.0 at the exact point where specimens were collected. No other annual fishes were found. Some specimens of Synbranchus sp. were also captured.

Etymology: Named in honor of Dalton Nielsen, the first collector of this new species, who sent me juvenile specimens which were not preserved for study.

Discussion

Simpsonichthys nielseni is a member of the S. notatus species group, which also includes S. notatus , S. radiosus , S. stellatus , S. rufus , S. trilineatus , S. auratus , and S. similis . This group is diagnosed by a typical frontal squamation pattern, in which there is a central A- scale with all margins free (Costa & Brasil, 2004; Costa, in press). This derived pattern is not found in other cynolebiatins (i.e., Simpsonichthys , Nematolebias Costa , Austrolebias Costa , Megalebias Costa , and Cynolebias Steindachner ) (Costa, 2001, 2002a, 2002b, in press), except in some specimens of Simpsonichthys ocellatus Costa, Nielsen & De Luca , from the Jequitinhonha River basin, Brazil. However, according to a recent phylogenetic study of the species of Simpsonichthys , S. ocellatus is not closely related to members of the S. notatus group (Costa, in press), which belong to a more inclusive clade exhibiting a typical spotted apomorphic color pattern in females (Fig. 2). This spotting does not occur in females of S. ocellatus .

Simpsonichthys nielseni is distinguished from all other species of the S. notatus group by the color pattern of the caudal fin in males, which comprises 6-7 light greenish yellow stripes parallel to fin rays (Fig. 1). This contrasts with the pattern consisting of bright dots scattered over the caudal fin, the plesiomorphic color pattern occurring in most other congeners (Costa, in press) (Fig. 5). However, S. radiosus also has similar caudal stripes, which however are reduced in number 3-5 (Costa & Brasil, 2004) (Fig. 6). Simpsonichthys nielseni may be easily distinguished from S. radiosus by having fewer dorsal-fin rays (21-22 vs. 23-26) and fewer anal-fin rays (19-21 vs. 21-23) in males, and by the presence of bright bars on caudal fin and elongated spots on dorsal-fin base, and absence of a black blotch on the flank in males.

Among species of the S. notatus group, only S. nielseni and S. stellatus possess a derived color pattern of elongated bright spots alternated by black zones on the basal portion of the dorsal fin in males (Figs. 1 and 5), which supports a hypothesis of sister group relationships (Costa, in press). Bright spots are longer in S. nielseni , and may be interpreted as short bars. In other species of this group, however, there is never a black zone on the dorsal-fin base (Fig. 6).