Prorivulus auriferus Costa, Lima & Suzart, 2004

Wilson J. E. M. Costa, 2004, A new killifish genus and species from the coastal plains of northeastern Brazil (Teleostei: Cyprinodontiformes: Rivulidae)., Zootaxa 642, pp. 1-10 : 3-7

Prorivulus auriferus Costa, Lima & Suzart , new species

(Figs. 1-2)

Holotype. UFRJ 5932 , male, 30.3 mm SL; Brazil: Estado da Bahia: Valença, coastal stream ( 24L 0503477 UTM 8505050 ); A. O. Lima & R. R. Suzart, 28 June 2003.

Paratypes. UFRJ 5933 , 1 female, 22.9 mm SL, and 3 juveniles, 13.1-15.5 mm SL ; UFRJ 5934 , 1 male, 28.5 mm SL, and 2 juveniles, 17.0-18.3 mm SL (c&s); collected with holotype .

Diagnosis: As for the genus.

Description: Morphometric data given in Table 1. Male larger than female, largest male 30.3 mm SL. 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 on 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 rounded. Caudal fin oval. Pectoral fin rounded, posterior margin on vertical through pelvic-fin base in male, just anterior to it in female. Tip of pelvic fin reaching between base of 2nd and 3rd anal-fin ray in male, and urogenital opening in female. Pelvic-fin bases in close proximity. Dorsal-fin origin on vertical through base of 8th or 9th anal-fin ray, and between neural spines of 19th and 21st vertebra. Anal-fin origin between pleural ribs of 13th and 15th vertebra. Dorsal-fin rays 9-10; anal-fin rays 14- 15; caudal-fin rays 32-33; pectoral-fin rays 13; pelvic-fin rays 7.

Scales large, cycloid. Body and head entirely scaled, except anterior ventral surface of head. Few scales on caudal-fin base; no scales on dorsal and anal fins. Frontal squamation E-patterned; E-scales overlapping medially; scales arranged in circular pattern around central A-scale without exposed margins. Longitudinal series of scales 31-33; transverse series of scales 8; scale rows around caudal peduncle 16. Contact organs absent. Supraorbital neuromasts 3 + 3.

Ventral process of angulo-articular broad. Rostral cartilage longer than wide, width about 65 % of length. Basihyal narrow, subrectangular, greatest width about 30 % of length; basihyal cartilage about 25 % of basihyal length. Interhyal vestigial, not ossified. Five branchiostegal rays. One or two teeth on second pharyngobranchial. First epibranchial straight. Distal process of second epibranchial absent. Uncinate process of third epibranchial long. Gill-rakers of first branchial arch 1 + 8. Two vomerine teeth. Dorsal tip of preopercle with short canal. Dermosphenotic present. Ventral process of posttemporal short. Neural prezygapophyses short, about 10 % of neural spine length in fifth caudal vertebra. Epipleural ribs rod-like. Total vertebrae 31-32.

Coloration in life: Male: Side of body light gray with irregular shaped golden blotches below lateral midline, and zigzag dark purplish gray stripe on lateral midline overlapped by oblique bars of same color scattered over flank. Dorsum light yellowish brown, venter light yellow. Postorbital pale brown, golden on ventral portion of opercle.

Infraorbital region and ventral surface of head light yellow. Lower jaw dark brown. Iris light yellow. Dorsal fin hyaline with pale gray dots and narrow yellow distal margin. Anal fin yellow with narrow black margin, light blue on base. Caudal fin light blue with pale yellow dots and dark gray distal margin. Pelvic fin yellow. Pectoral fin yellowish hyaline.

Female: Side of body light gray with zigzag dark gray to black stripe on lateral midline. Dorsum light brown, venter light gray. No distinctive black spot on posterior portion of caudal peduncle nor on caudal-fin base. Postorbital region with black stripe, pale golden on ventral portion of opercle. Infraorbital region and ventral surface of head light gray. Lower jaw dark gray to black. Iris light yellow. Dorsal and anal fins pale yellow with transverse rows of small dark gray spots; distal margin of anal fin black. Caudal fin light yellow with narrow dark gray bars. Paired fins hyaline.

Distribution: Known only from the type locality, a coastal plain brook in the Municí- de Valença, northeastern Brazil.

Habitat notes: The type series was collected in a shallow (about 40 cm deep), small freshwater brook within a forest, near a salt water canal. It is situated in a coastal region, with a net of canals forming a series of small islands. The water was reddish brown, acid (pH 4.0), not turbid. The only other fish species found was the characid Hyphessobrycon cf. itaparicensis Lima & Costa .

Etymology: From the Latin auriferus (auriferous), referring to the male color pattern consisting of golden spots on the flank.

Discussion

Five synapomorphies listed by Costa (2004a) for the group including Rivulus and the clade comprising all annual rivulids, are not present in P. auriferus : E-scales not overlapped (Fig. 3A; reversed in the clade comprising Simpsonichthys , Cynolebias , Megalebias , Austrolebias ), shortened uncinate process of the third epibranchial (Fig. 4D; unambiguous), articular face of the distal edge of the first hypobranchial anteriorly expanded (Fig. 4F; unambiguous), ventral process of the angulo-articular narrowed (Fig. 4H; unambiguous), and posterior flange of the cleithrum absent (Fig. 4J; unambiguous). These synapomorphies support the monophyly of the group comprising Rivulus and the annual fish clade (Fig. 5). Prorivulus auriferus present the plesiomorphic conditions for these characters, as occurring in Kryptolebias and in aplocheiloids non-rivulids (i. e., nothobranchids and aplocheilids): E-scales overlapped (Fig. 3B), uncinate process of the third epibranchial long (Fig. 4C), articular face of the distal edge of the first hypobranchial not anteriorly expanded (Fig. 4E), ventral process of the angulo-articular broad (Fig. 4G), and posterior flange of the cleithrum present (Fig. 4I).

Two synapomorphies listed by Costa (2004a) support monophyly of the group comprising Prorivulus , Rivulus and the annual fish clade (Fig. 5): unossified interhyal (unambiguous) and absence of the distal process of the second epibranchial (Fig. 4B; unambiguous). In Kryptolebias and in aplocheiloids non-rivulids the interhyal is ossified and there is a conspicuous distal process on the second epibranchial (Fig. 4A).

The presence of five branchiostegal rays in Prorivulus is interpreted as autapomorphic. Other aplocheiloids have six branchiostegal rays, except the cynolebiatine M. wolterstorffi (Ahl) with eight rays, the Plesiolebiatini genus Stenolebias and Rivulus romeri also with five rays ( Costa, 1998, 2003b). Stenolebias is an annual fish genus, member of the Plesiolebiatini clade, which includes other genera with six rays ( Costa, 1998), and R. romeri is a member of the Rivulus atratus species group , which also includes several species with 6 rays ( Costa, 2004b). Therefore, reduction to five branchiostegal rays is considered a homoplastic condition, occurring in three distinct rivulid lineages.