Plesiolebias fragilis, Wilson J. E. M. Costa, 2007

Wilson J. E. M. Costa, 2007, Taxonomy of the plesiolebiasine killifish genera Pituna, Plesiolebias and Maratecoara (Teleostei: Cyprinodontiformes: Rivulidae), with descriptions of nine new species., Zootaxa 1410, pp. 1-41 : 21-25

Plesiolebias fragilis , new species

(Figs. 14-15)

Plesiolebias lacerdai non P. lacerdai Costa ; Costa, 1998a: 328 (misidentification).

Material examined. Holotype. UFRJ 6411 (male, 19.7 mm SL); Brazil: Estado do Tocantins: temporary pool in left rio Formoso floodplains, rio Javaés drainage, rio Araguaia basin, road BR-242, between Formoso do Araguaia and São João do Javaés, 11º47’31.6”S, 49º45’54.7”W; W. J. E. M. Costa, C. P. Bove, J. Paz & A. Oliveira, 15 April 2006.

Paratypes. Brazil: Estado do Tocantins: rio Araguaia basin: UFRJ 6412 (2 females, 20.1-20.7 mm SL) ; MCP 40499 (1 male, 19.6 mm SL, 1 female, 20.2 mm SL); collected with holotype . UFRJ 5262 (2 males, 15.7-16.0 mm SL, 2 females, 17.0-19.8 mm SL) ; UFRJ 5049 (2 males, 14.3-16.8 mm SL, 6 females, 14.2- 16.0 mm SL [c&s]), Parque Nacional do Araguaia, ilha do Bananal; G. C. Brasil et al., April 1999 . UFRJ 3793 (1 male, 14.0 mm SL, 23 females, 15.1-18.3 mm SL); rio Formoso floodplains; D. T. B. Nielsen, A. Carletto & A. de Luca, 6 April 1996 .

Diagnosis. Distinguished from all other congeners by the following combination of characters: filamentous ray on pelvic fins in males (vs. filamentous ray absent); pelvic-fin rays 8 (vs. 7); eye yellow in males (vs. bright green); flank with oblique black bars in males (vs. black bars absent); no red stripe on anterior portion of flank in males (vs. red stripe present); basal portion of dorsal fin red in males (vs. with transverse rows of dark red and white spots); a black spot on posterior portion of anal fin in males (vs. black spot absent); body depth 23.3-25.4 % SL in males, 22.2-25.7 % SL in females (vs. 28.6-32.6 % SL in males, 26.4-30.3 % SL in females); sparse bright dots on flanks in males (vs. oblique rows of bright dots on flank); 3 white bars on basal portion of anal fin in males (vs. 4-5); no black bar on preopercle (vs. black bar present on preopercle); 5-7 oblique bars on flank in females (vs. 8-9); 24-25 scales in longitudinal series (vs. 22-23).

Description. Morphometric data appear in Table 3. Largest male examined 19.7 mm SL, largest female examined 20.2 mm SL. Dorsal profile slightly convex from snout to end of dorsal-fin base, approximately straight on caudal peduncle. Ventral profile gently convex from lower jaw to end of anal-fin base, about straight on caudal peduncle. Body slender, compressed. Greatest body depth at level of pelvic-fin base. Jaws short, snout blunt.

Tip of both dorsal and anal fins rounded, without filaments. Caudal fin rounded. Pectoral fins elliptical, posterior margin reaching vertical through urogenital papilla and anal-fin origin in males, between pelvic-fin base and anus in females. Pelvic fins pointed in males, terminating in long filament, with tip reaching between base of 5th and 8th anal-fin rays; tip of each pelvic fin reaching base of 3rd anal-fin ray in females. Pelvic-fin bases medially united. Dorsal-fin origin on vertical between base of 1st and 3rd anal-fin rays, and between neural spines of 9th and 11th vertebrae. Anal-fin origin between pleural ribs of 8th and 9th vertebrae. Dorsal-fin rays 11-12; anal-fin rays 15-17; caudal-fin rays 23-25; pectoral-fin rays 12; pelvic-fin rays 8.

Scales large, cycloid. Body and head entirely scaled, except anterior ventral surface of head. Body squamation extending over anterior 25 % of caudal fin; no scales on dorsal and anal-fin bases. Frontal squamation G-patterned; E-scales overlapping medially; scales arranged in regular transverse pattern. Two supraorbital scales. Longitudinal series of scales 24-25; transverse series of scales 7; scale rows around caudal peduncle 12. One to three minute contact organs on posterior margin of each scale of ventral portion of flanks in males.

Cephalic neuromasts: supraorbital 6 + 2, parietal 2, anterior rostral 1, posterior rostral 1, infraorbital 1 + 23-25 + 1, preorbital 3-4, otic 1, post-otic 1, supratemporal 1, median opercular 1, ventral opercular 1, preopercular2 + 9, mandibular 6, lateral mandibular 5. One neuromast on center of each scale of lateral line of trunk. Two neuromasts on caudal-fin base.

Basihyal narrow, longest width about 20 % of length; basihyal cartilage about 25 % of basihyal length. Five branchiostegal rays. Five teeth on second pharyngobranchial. Gill-rakers of first branchial arch 1 + 8. Vomerine teeth absent. Ventral process of posttemporal absent. Total vertebrae 23-25.

Coloration. Males: Sides of body gray with 6-8 bars, black and well defined on anterior two thirds of flank, reddish brown and diffuse on caudal peduncle region; few greenish blue dots scattered on flanks. Dorsum gray. Venter white, with transverse dark gray marks. Side of gray, opercular region pale greenish golden; short oblique black bars on dorsolateral portion of head posterior to orbit and short oblique black infraorbital bar. Jaws dark gray. Iris yellow, with black bar through center of eye. Dorsal fin red, distal portion hyaline; small white spot on middle of fin base, and short oblique white bar on posterior margin. Anal fin reddish black, with three short white bars on its basal half, anteriormost bar wider, often forming triangular mark, corresponding to fusion of two anteriormost bars of other species of Plesiolebias ; faint light blue bar on posterior portion of fin; black blotch on posterior portion of fin visible only in preserved specimens. Caudal fin gray, with transverse rows of small light gray spots on basal region of fin. Pectoral fins hyaline. Pelvic fins black, with two white bars, anterior bar near anterior margin of fin and posterior bar on posterior margin.

Females: Sides of body light brownish gray, with 5-7 narrow oblique black bars. Dorsum light brownish gray. Venter white. Sides of head gray, pale greenish yellow on opercle. Jaws gray. Iris pale yellow, with gray bar through center of eye. Fins hyaline.

Etymology. From the Latin fragilis (fragile), an allusion to the fragility of this tiny (i. e., pygmy size) new species.

Distribution and habitat. Plesiolebias fragilis occurs in seasonal swamps of the middle rio Araguaia basin (Fig. 13), in the region of ilha do Bananal, Estado do Tocantins, Brazil. This is an area of transition between the savannas of central Brazil (Cerrado) and the Amazonian forest. Concentrated in these swamps are one of the richest known assemblages of sympatric seasonal rivulids (Costa, 1998a), with a total of seven species. Besides P. fragilis , the following species are found here: Trigonectes rubromarginatus Costa , Simpsonichthys costai (Lazara) , Simpsonichthys semiocellatus (Costa & Nielsen) , Pituna poranga Costa , Maratecoara lacortei (Lazara) , and Plesiolebias aruana (Lazara) .