Cnesterodon pirai, Aguiler, Gastón, Mirand, Juan Marcos & Azpelicuet, María De Las Mercedes, 2009

Aguiler, Gastón, Mirand, Juan Marcos & Azpelicuet, María De Las Mercedes, 2009, A new species of Cnesterodon (Cyprinodontiformes: Poeciliidae) from a small tributary of arroyo Cuñá-Pirú, río Paraná basin, Misiones, Argentina, Zootaxa 2195, pp. 34-42 : 36-41

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.

Figures

FIGURE 1. Cnesterodon pirai n. sp., CI-FML 3853, holotype, male, 26.6 mm SL (top); CI-FML 3965, paratype, female, 28.2 mm SL (bottom).

FIGURE 2. Gonopodium of Cnesterodon pirai, paratype CI-FML 3855.

FIGURE 3. Distribution of Cnesterodon pirai. Dot indicates type locality.

FIGURE 4. Consensus tree under a- equal weight; b- implied weighting (K = 3 - 10); c- implied weighting (K = 11 - 16). The GC / relative Bremer support values are shown. Question marks in GC values represent negatives values, which are an artifact of the method, assigned to weakly supported nodes. Unsupported nodes are shown as collapsed.

Tables

TABLE 1. Descriptive morphometrics of specimens of Cnesterodon pirai.

Character	mean	range mean	range
Standard length (mm) 26.6	22.5	19.8–26.6 24.0	21.8–27.8
Percent of standard length
Head length 19.5	21.1	19.3–22.6 22.9	20.8–26.3
Snout-occipital 19.3	20.3	18.9–22.7 20.7	18.7–23.9
Predorsal distance 52.4	52.8	50.5– 54.5 60.7	57.5–62.9
Dorsal-fin base length 10.8	11.0	9.6– 12.2 11.0	9.1–14.5
Anal-fin base length 6.9	7.3	6.6–8.3 9.2	7.7–10.4
Body depth 21.1	20.0	19.2–21.2 25.9	22.6–29.8
Pre-pelvic length 23.4	24.9	23.2–27.2 44.1	41.7–46.4
Pre-anal length 33.2	33.0	30.8–35.1 57.3	54.4–59.3
Post-anal length 64.6	65.2	61.7–70.1 36.4	34.5–39.2
Caudal peduncle depth 16.1	16.0	14.9–17.4 14.4	13.7–15.6
Percent of head length
Snout length 19.7	20.9	16.7–25.9 22.2	16.8–28.7
Orbital diameter 36.1	37.4	34.6–40.2 37.5	30.6–42.8
Postorbital length 46.3	47.3	41.1–53.2 55.1	49.6–60.6