Cnesterodon holopteros, Paulo H. F. Lucinda, Thomas Litz & Roberto Recuero, 2006

Paulo H. F. Lucinda, Thomas Litz & Roberto Recuero, 2006, Cnesterodon holopteros (Cyprinodontiformes: Poeciliidae: Poeciliinae), a new species from the Republic of Uruguay., Zootaxa 1350, pp. 21-31 : 24-30

Cnesterodon holopteros , n. sp.

(Figs 2-4; Table 1)

Holotype (Fig. 2). MUNHINA 3218 (male, 19.8 mm SL), Arroyo Catalancito, Río Cuareim drainage, Ruta 30, km 156.4, 30°37.87’S, 56°22.75’W, Departmento Artigas, Uruguay, P. Laurino, T. Litz, E. Perujo, I. Perujo and H. Salvia, 16 Aug 2002.

Paratypes. Uruguay. Departmento Artigas. MCP 39803 (2, 19.5-23.4 mm SL) , MUNHINA 3219 (2, 17.9-20.3 mm SL) and UNT 1946 (4 [2 c&s], 19.4-28.1 mm SL), paratopotypes, collected with the holotype . UNT 1964 (3, 11.4-14.5 mm SL), lagoon near Franquia, 30°13.05’S, 57°37.29’W, P. Laurino, T. Litz, E. Perujo, F. Prieto and H. Salvia, 18 Mar 2003 .

Diagnosis. Cnesterodon holopteros is distinguished from its congeners by (1) a series of small dark brown dots present along predorsal portion of first, second or third lateral scale rows, which are associated with vertical bars along lateral surface of body (Figs. 2-3); (2) eight or nine (rarely seven) dark brown vertical bars along lateral surface of body, which may reach lower part of belly (i.e., at level of ventral profile) in females, the length of each bar corresponding approximately to the vertical depths from one to three scales (Fig. 3); (3) bony style at male gonopodium tip long and gently arched, narrowing towards tip, forming a distal filament and bearing a V-shaped membrane restricted to its proximal third (Fig. 4); (4) four branchiostegal rays in females; and (5) unbranched pelvic-fin rays (branched pelvic-fin rays [except first one] in remaining Cnesterodon species).

Description. Morphometric data appear in Table 1. Ranges of standard length: 19.4 to 28.1 mm (females); 11.4 to 22.7 mm (males). Body compressed laterally. Body width in predorsal region uniform, about half body depth. Post-dorsal region compressed near caudal peduncle. Predorsal profile convex. Dorsal-fin base convex. Postdorsal profile slightly concave. Pre-anal profile convex. Anal-fin base oblique. Post-anal profile almost straight. Dorsal fin with semicircular border, located posterior to mid-body. Origin of dorsal fin in females on vertical passing through base of third anal-fin ray; in males, origin of dorsal fin posterior to vertical passing through origin of anal fin. Pectoral fin inserted high on each side of body, at level of center of orbit. Pelvic fins small, pointed and not reaching origin of gonopodium in adult males; not reaching origin of anal fin in females. Anal fin of females with straight ventral border. Origin of anal fin of females closer to caudal peduncle than to snout tip. Origin of anal fin of males closer to snout tip than to caudal peduncle. Mouth superior, aligned almost with upper border of pupil.

Dorsal-fin rays: 8* [10], 9 [2]. Pectoral-fin rays: 8 [2], 9* [4], 10 [4]. Pelvic-fin rays (all unbranched): 4* [2] (males); 5 [4] (females). Anal-fin rays (females): 10 [5]. Anal-fin rays (males): 8 [3], 9* [4]. Caudal-fin rays: 22 [2], 24 [4], 25 [3], 26* [3]. Predorsal scales (females): 13 [1], 14 [3]. Longitudinal series scales: 29 [2], 30* [6], 31 [3]. Scales around caudal peduncle: 16* [12]. Scales in transverse row: 8* [11]. Pleural ribs: 16 [2]. Epipleural ribs: 7 [1, female], 9 [1, male]. Vertebrae: 33 [2].

Preorbital ramus of cephalic sensory system represented by two or three grooved neuromasts. Preorbital canal absent. Anterior portion of supraorbital ramus (pores 1 and 2a) parallel to upper lip, with five inconspicuous neuromasts on each side. Posterior portion of supraorbital ramus (pores 2b, 3, 4a) composed of three grooved neuromasts. Posterior remnants of infraorbital ramus represented by three neuromasts (pores 4b, 5, 6a) and by one short groove (pores 6b and 7). Preopercular ramus represented by large groove along preopercular posterolateral border and by prolonged canal along preopercle ventral border by four neuromasts. Opercular canal absent. Mandibular ramus composed of two or three superficial neuromasts (pores Z, Ya, and Yb) on anterior border of ventral surface of mandible and by one superficial neuromast near maxillary distal end (pore W).

Gonopodial complex and male gonopodium. Gonopodial complex composed of nine gonactinosts. Functional gonapophyses absent. Gonactinosts 2, 3, 4 fused. Gonactinost 4 with wing-like expansions. Ligastyle absent. Gonopodium symmetrical. Eight or nine gonopodial rays. Anal-fin ray (R1) and anal-fin ray 2 (R2) unbranched and short. R1 with six segments. R2 with nine segments. R3 with 26 segments. At tip, long slender bony style bearing narrow membrane produced in terminal filament. Four to six paired retrorse spines on distal segments of posterior ramus of anal fin of ray 4 (R4p). Anterior ramus of anal ray 5 (R5a) with subdistal and discrete dorsal curvature and terminating in a retrorse claw. Anal rays 6, 7, 8 (R6, R7, and R8) branched. Distal segments of R6 and R7 partially ankylosed. Bony style at tip of gonopodium in adult males comparatively long and very slightly and gently arched, narrowing towards tip and forming a short distal filament. Membrane on bony style V-shaped and restricted to proximal third of bony style (Fig. 4).

Color in alcohol. Eye black, with greenish-brown pupil. Background color cream yellow. Borders of scales and subjacent skin with numerous brown chromatophores, conferring a reticulate pattern to body sides. Dorsum darker than ventral region. Head dorsum dark brown. Median faint brown line along predorsal surface. Median dark brown line along preanal surface. Fins hyaline. Fin rays with two rows of brown chromatophores on each side, along entire ray. Males bearing eight or nine (rarely seven) dark brown vertical bars along sides of body, corresponding approximately to vertical depth of one scale and mostly confined to midline. Females bearing eight or nine (rarely seven) dark brown vertical bars along sides of body, corresponding approximately to vertical depth of one to three scales and sometimes reaching belly (at level of ventral profile). Series of small dots present along predorsal portion of first, second, or third lateral scale row. Large dark brown blotch on each side of ventral portion of body near male gonopodium, meeting midventral post-anal line.

Comparisons. Characters cited in the “Diagnosis” support the recognition of this species as distinct from its congeners. Cnesterodon holopteros can also be distinguished from its congeners as follows: It is distinguished from C. omorgmatos and C. raddai by having dark brown blotches along sides of body (forming bars vs. circular or irregular, respectively); from C. hypselurus by the absence of a longitudinal dark brown stripe along flanks (vs. presence of such a stripe in C. hypselurus ); from C. septentrionalis Rosa & Costa, 1993 in having a greater number of longitudinal scales (29-31 vs. 25-26, respectively) and more transverse scale rows between dorsal and anal fins (8 vs. 7, respectively). The absence of small scales covering the lateral and ventral region of body below the pectoral fin in adult females and the pointed snout distinguishes C. holopteros from C. brevirostratus Rosa & Costa, 1993 . Cnesterodon holopteros is readily distinguished from C. iguape (Lucinda, 2005:131; Fig. 5a) by the smaller post-gonopodial blotch at the level of the ventral profile in adult males. Cnesterodon holopteros is distinguished from C. carnegiei by the number of epipleural ribs (7-9 vs. 10-12) and by the colour pattern.

Ecological notes. This species is known from the Arroyo Catalancito and a lagoon near Franquia, both locations of which are located in the río Uruguay basin, within the department of Artigas, Uruguay (Fig. 1). The type locality is a small, shallow, sidewater creek tributary of the río Cuareim (= rio Quaraí), and is characterized by rocks, loose stones, and gravel bottom with clear rapidly-flowing water. Grass and other vegetation were present in the margins, and dense stands of Echinodorus uruguayensis grew in some areas. Cnesterodon holopteros was found exclusively in shallow, densely vegetated areas along the stream margins. The fish fauna in the arroyo Catalancito was equivalent to that described by Pessano et al. (2005). However, the second location was a large lagoon of the río Uruguay, near Franquia, with a diameter of approximately 100 meters. This location is situated only a few kilometres south of the mouth of the río Cuareim, which is tributary to the río Uruguay. Cnesterodon holopteros was also collected in shallow, densely vegetated areas along the margins of the lagoon. Ecological data at the collecting site (18 March 2003) were air temperature: 26°C, water temperature 28°C, pH 6.8, and conductivity 78 µS/cm. About 30 fish species may be present in this lagoon, based on Sverlij et al’s (1998) report for the río Uruguay.

It is noteworthy that C. decemmaculatus was also collected at a few locations in this hydrographic region, but compared to other hydrographic regions in Uruguay fishes of the genus Cnesterodon are rare, and other poeciliod species such as Phalloceros caudimaculatus (Hensel, 1868) and Jenynsia onca Lucinda, Reis & Quevedo, 2002 apparently are absent. These results are in accord with Pessano et al. (2005) and Sverlij et al. (1998), who did not report P. caudimaculatus or J. onca from either the río Cuareim or río Uruguay drainages. In the description of J. onca , the distribution was reported to include the río Ibicuí and río Negro drainages (which are situated, respectively, north and south of the area under discussion) (Lucinda et al., 2002), but not the area in between. This supports the hypothesis that the río Cuareim region differs hydrographically in some respects from northern and southern drainages of the río Uruguay. However, Devincenzi & Teague (1942) reported the collection of Cnesterodon decemmaculatus and Jenynsia lineata (Jenyns, 1842) (the latter probably a misidentification of Jenynsia multidentata (Jenyns, 1842 )) from the Laguna de Curtiembre, tributary to the middle río Uruguay, situated a few kilometres north of the city of Paysandú; about 200 km south of the locations we investigated.

Distribution. Cnesterodon holopteros is currently known to inhabit the Arroyo Catalancito and a lagoon near Franquia, Río Cuarein basin, Departmento Artigas, Uruguay (Fig. 1).

Etymology. From the masculine, nominative, singular, Greek adjective olopteroj [= holopteros], meaning the whole (i. e. undivided) fins, in reference to the unbranched pelvic-fin rays.

Phylogenetic relationships. A total of 2209 equally most parsimonious cladograms were found (length = 755, CI = 0.35, RI = 0.75), with three equally most parsimonious trees describing variation in topology concerning Cnesterodon species relationships. Cnesterodon topologies obtained are partially isomorphic with those discussed in Lucinda (2005). However, the inclusion of C. holopteros resolved the basal polytomy of Lucinda´s hypothesis (2005: 262; Fig. 2). All most parsimonious cladograms indicate: (1) C. raddai is sister to all other Cnesterodon species; (2) Cnesterodon sp. n. B is sister to all remaining Cnesterodon species; and (3) Cnesterodon holopteros is sister to a clade composed of C. decemmaculatus , C. carnegiei , C. omorgmatos , C. brevirostratus , C. septentrionalis , C. hypselurus , and C. iguape . A strict consensus cladogram appears in Fig. 5.

Discussion

For the phylogenetic analyses, states for the new species are the following for Lucinda & Reis’ (2005) characters 1 to 144: 002300011? 11-1010000 11-0101111 0112030201 0210100300 003---1102 1100210102 0020000112 0110041000 1110 ----- 0 01000---00 1100102000 0010101210 0010000001 0100. The character states exhibited by Cnesterodon holopteros allow its recognition as a member of the monophyletic genus Cnesterodon , which is diagnosed by the nine uniquely derived and unreversed features (Lucinda, 2005: 261). Global parsimony of character states in the consensus tree also supports C. raddai as sister to a clade composed of all other Cnesterodon species. Cnesterodon sp. n. B is sister to all remaining Cnesterodon species; and Cnesterodon holopteros is sister to a clade composed of C. decemmaculatus , C. carnegiei , C. omorgmatos , C. brevirostratus , C. septentrionalis , C. hypselurus , and C. iguape . The generic phylogenetic relationships are not completely satisfactory given the polytomy ( C. carnegiei , C. omorgmatos , ((( C. brevirostratus , C. septentrionalis ), ( C. hypselurus , C. iguape )))), but the cladogram expresses the up-to-date state of knowledge of the relationships among Cnesterodon species. However, it represents an improvement on the state of knowledge concerning Cnesterodon infrageneric relationships, given that inclusion of C. holopteros resolved the basal polytomy of Lucinda’s (2005) hypothesis (2005: 262; Fig. 2). This is an example on how the discovery of new characters and/or species can help in the clarification of phylogenetic relationships.

It is likely that additional undescribed Cnesterodon species will be discovered as a result of ever-increasing collecting efforts in scarcely sampled and unsampled South American regions, and to a marked increase in attention to poeciliid fishes in recent years.