Cnesterodon pirai, n. sp.

(Fig. 1, 2)

Holotype: CI-FML 3853 male, 26.6 mm SL, Argentina, Misiones, Aristóbulo del Valle, río Paraná basin, arroyo Almeida, tributary of arroyo Cuña Pirú (27º 00' 24'' S 54º 50' 22'' W). G. Aguilera and J. M. Mirande, December 6, 2004.

Paratypes: CI-FML 3854, 4 ex., 15.5−18.8 mm, collected with holotype; AI 223, 6 ex., 21.0− 27.8 mm, Argentina, Misiones, Aristóbulo del Valle, río Paraná basin, arroyo Almeida, affluent of arroyo Cuña Pirú, G. Aguilera, J. M. Mirande and G. Terán, November 23, 2008; ANSP 187060, 4 ex., 21.6−22.8 mm, Argentina, Misiones, Aristóbulo del Valle, río Paraná basin, arroyo Almeida, tributary of arroyo Cuña Pirú, G. Aguilera, J. M. Mirande and G. Terán, November 23, 2008; CI-FML 3855, 2 ex. C&S, 15.9−20.7 mm SL, collected with the holotype; CI-FML 3965, 8 ex., 20.0− 28.2 mm, Argentina, Misiones, Aristóbulo del Valle, río Paraná basin, arroyo Almeida, tributary of arroyo Cuña Pirú, G. Aguilera, J. M. Mirande and G. Teran, November 23, 2008.

Diagnosis: Cnesterodon pirai is diagnosed by the combination of the following characters: 6 to 8 irregular dashes on flanks, ranging from oval to vertical stripes on females and 7 to 9 irregular dashes ranging from oval to circular dots on males (dashes both on males and females covering 1 or 2 scales in transverse row); absence of a large post-gonopodium blotch on ventral profile in adult males; lack of a distal filament on gonopodium; absence of longitudinal dark-brown band along flank; snout pointed and long (16.7–28.7 % HL); possession of 12–13 epipleural ribs; medial surface of ascending process of premaxilla approximately straight; presence of teeth on fourth ceratobranchial; distal portion of third and fourth gonactinosts separate, except by tip of third gonactinost; fifth gonactinost free; and presence of a constriction on unpaired appendix of gonopodium.

Description: Body compressed, pre-anal region width about 1.14 of body depth; post-anal region compressed towards peduncle. Dorsal profile slightly concave from snout tip to vertical through middle eye; convex from vertical through middle eye to third or fourth scale anterior to dorsal-fin origin, and straight to dorsal-fin origin; convex from dorsal-fin origin to caudal fin. Preanal profile convex. Anal-fin base oblique dorsally. Postanal profile slightly convex. Dorsal-fin origin at vertical through third anal-fin ray in females and posterior to anal-fin base in males. Pectoral-fin insertion just ventral to horizontal line through middle of eye. Pelvic fin small, below pectoral-fin insertion in males, and at vertical through end of the longest pectoralfin ray in females. Anal-fin insertion just anterior to vertical through dorsal-fin origin in females. Gonopodial insertion at vertical through tip of longest pectoral-fin ray in males. Mouth superior.

Morphometric measurements expressed as percents of SL are presented in Table 1. Counts of 23 specimens including the holotype are as follow: predorsal scales 13 (18*), 14 (4), 15 (1); longitudinal scales series 29 (1), 30 (13*), 31 (8), 32 (1); transverse scales 10 (22*), 11(1); scales around the peduncle 16 (23*); dorsal-fin rays 8 (23*); anal-fin rays (females) 10 (15); pectoral-fin rays 11 (1), 12 (22*); caudal-fin rays 25 (1), 26 (16*), 27 (6). Counts on C&S specimens are as follow: pelvic-fin rays: 4(2) (males), 5(1) 6(1) (females); pleural ribs 14(3), 15(1); epipleural ribs 12 (3), 13 (1); vertebrae 31 (1), 32 (3); gonopodial rays (males) 8 (2).

Morphometric measures holotype males (n=8) females (n=15) Gonopodium (Fig. 2): Gonopodial complex composed of 9 gonactinosts. Gonactinosts 2, 3, and 4 fused. Eight anal-fin rays. R1 unbranched with 7 segments. R2 unbranched with 8 segments. R3 with 25 segments, tiny serrations at subdistal segments, and a bony style at tip. Bony style not completely ossified, slender, curved dorsally, with a ventral chondral apophysis. Semicircular membrane reaching middle of bony style, not forming a distal filament. Posterior ramus of R4 with four pairs of retrorse spines located on segments 7 to 10 before tip. Distal portion of R5 curved dorsally, ending in a retrorse claw. R6 and R7 branched and distal segments partially ankylosed.

Cephalic sensory system: Preorbital ramus composed by 4 superficial neuromasts. Anterior portion of supraorbital ramus (pores 1 and 2a) composed by 3 neuromasts; posterior portion of supraorbital ramus (pores 2b, 3 and 4) composed by 3 neuromasts. Infraorbital ramus composed by 3 superficial neuromasts (pores 4b, 5 and 6a), and a groove with 1 neuromast (pores 6b and 7). Preopercular ramus composed by a vertical groove with 3 neuromasts, and an inferior canal with 4 pores. Mandibular ramus composed by 5 superficial neuromasts.

Coloration of live specimens: Body dorsum yellowish green, darker from midlateral region to ventral portion of body; belly white; iridescent green blotch on opercle; fins light yellow.

Coloration of preserved material: Background yellowish; reticular pattern formed by dark brown chromatophores following border of scales. Predorsal line very faint or absent. Dashes on flanks formed by dark-brown chromatophores covering 1 or 2 scales (never reaching dorsal and ventral profile of body), mostly on midline; females with 6 to 8 irregular dashes, ranging from oval to vertical stripes, and males with 7 to 9 irregular dashes ranging from oval to circular dots. Males with or without blotch of dark-brown chromatophores on flanks situated opposite to dorsal-fin insertion, below midline of body side; blotches wider dorsally and narrowing to ventral portion, contacting or not each other ventrally. Midventral postanal line contacting or not ventral portion of blotches, and extending to caudal fin.

Distribution: Cnesterodon pirai is only know from its type locality, arroyo Almeida, affluent of arroyo Cuñá-Pirú, río Paraná basin, Aristóbulo del Valle, Misiones, Argentina (Fig. 3). In spite of the collecting effort in different streams of Misiones province, especially in the Cuñá-Pirú basin, C. pirai was not found in other sites.

Ecological notes: The stream where the new species lives is narrow (2 m wide on its widest section) and shallow, with falls about 80 cm depth, and moderately slow current. It is a tributary of the Cuña-Pirú stream (above Salto Encantado, a fall with 40 m depth); the creek only has 700 m from its headwaters to the confluence with Cuñá-Pirú. The rocky stream bed, covered by detritus over 50% of its surface, presents small pools and glides. Cnesterodon pirai was especially found forming schools of juveniles and adults in pools.

Etymology: The specific epithet pirai derives from the Guarani words “ pirá ”, meaning fish and the diminutive “ í ”, in allusion to the small size of the fishes belonging to the genus Cnesterodon . A noun in apposition.

Phylogenetic relationships: Codification of Cnesterodon pirai for the character states proposed by Lucinda & Reis (2005), characters 1 to 144, is as follows: 0 0 23000112 1021010000 1100101011 0 112030201 0 210100300 003---1102 11[06][03] 210102 0 0 20200112 0 0 10041000 1110?????0 01010???00 1100102000 0 0 10101210 0 0 10000001 0 100. The analysis performed under equal weights produced 1938 equally most parsimonious trees, of 758 steps (CI: 0.35; RI: 0.76). The topology of consensus tree (Fig. 4 a) shows a basal polytomy formed by Cnesterodon decemmaculatus, C. radai, C. sp. B and C. holopteros . This is the sister group of a polytomy formed by Cnesterodon carnegiei, C. omorgmatos, C. hypselurus, C. iguape, C. brevirostratus, C. septentrionalis and C. pirai .

Under implied weighting with concavities (K) range from 3 to 10 (Fig. 4 b) the consensus tree is partially resolved. There is a polytomy in the base of the tree formed by Cnesterodon raddai, C. sp. B, and a clade composed by the remaining species of the genus; within this clade, C. pirai forms a tricotomy with ( C. brevirostratus + C. septentrionalis), and ( C. hypselurus + C. iguape). With K from 11 to 16 (Fig. 4 c) the topology of the consensus tree varies slightly; C. decemmaculatus becomes basal to all other species of the genus, while the relationships of C. pirai remain stable.