A new species of Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the upper rio Paraná basin, Brazil

A new species of Corydoras is described from three tributaries of the rio Ivaí drainage, upper rio Paraná basin, Paraná State, Brazil. The new species can be distinguished from most of its congeners by the presence of three nasal pores. Other diagnostic features are the lower number of serrations in posterior margin of pectoral and dorsal spines and presence of four to six small black blotches along the midline of the flank. The possible mimetic relationship between the new species and Characidium heirmostigmata is discussed.


Material and Methods
Measurements were obtained using digital caliper to the nearest 0.1 millimeter. Morphometric and meristic data were taken following Reis (1997), excepting the length of the anal-fin spine that is absent in all Corydoradinae. The length of the pectoral-fin spine was included in the morphometric analysis and was taken from its base to its distal tip. Morphometrics are reported as percentages of standard length (SL) and head length (HL). Homology of barbels follows Britto & Lima (2003). Some specimens were cleared and stained (c&s) according to protocol of Taylor & Van Dyke (1985) for osteological analysis. Osteological terminology was based on Reis (1998), excepting by using parieto-supraoccipital instead of supraoccipital (Arratia & Gayet, 1995) and compound pterotic instead of pteroticsupracleithrum (Aquino & Schaefer, 2002). Counts of vertebrae followed Britto et al. (2009). In the description, numbers in brackets represent the total number of specimens with those counts. Numbers with an asterisk refer to the counts of the holotype. Comparative data of Corydoras diphyes were obtained from Axenrot & Kullander (2003
Eye rounded, located dorso-laterally on head; orbit delimited dorsally by frontal and sphenotic, ventrally by infraorbitals. Anterior and posterior nares close to each other, only separated by a flap of skin. Anterior naris tubular. Posterior naris close to anterodorsal margin of orbit, separated from it by a distance equal to diameter of naris. Mouth small, subterminal, width nearly equal to bony orbit diameter. Maxillary barbel short, not reaching anteroventral limit of gill opening. Outer mental barbel slightly longer than maxillary barbel. Inner mental barbel fleshy, base separated to its counterpart; insertion of barbell in middle of lower lip. Small rounded papillae covering entire surface of all barbels, upper and lower lips, and isthmus.
Mesethmoid short, posterior portion partially exposed and bearing minute odontodes. Nasal slender, curved laterally, anterior portion of inner margin laminar; mesial border contacting only frontal; with three nasal pores. Frontal elongated, narrow, width less than half entire length; anterior projection short, size smaller than nasal length; epiphyseal branch of supraorbital canal short, pore opening located mesially on frontals. Frontal fontanel large, oval; posterior Dorsal-fin rays II,8*(20), II,9(1), posterior margin of dorsalfin spine with 7-10 serrations, disposed on distal half of the spine; nuchal plate exposed with minute odontodes; spinelet short; spine short, adpressed distal tip not surpassing base of last branched dorsal-fin ray, posterior margin with small odontodes. Pectoral-fin rays I,8; posterior margin of pectoral spine with 16-19 moderate developed serrations, disposed along entire length of posterior margin or absent close to the insertion of spine (Fig. 2a). Pelvic-fin rays i,5. Anal-fin rays i,6. Caudal-fin rays i,12,i, generally three dorsal and ventral procurrent rays, respectively; bilobed, with superior lobe slightly larger than inferior one; lobes with rounded distal border.
Initially, the new species was identified as Corydoras flaveolus by Graça & Pavanelli (2007). However analyzing material of C. flaveolus from the rio Tietê basin, including tributaries of rio Piracicaba, some morphological differences that allowed to diagnose the two species became evident. The snout of Corydoras lacrimostigmata is slightly pointed and the dorsal profile of the head is gradually concave (Fig.  1), whereas in C. flaveolus the snout is roughly rounded and the dorsal profile of the head is abruptly concave (Fig. 4). In addition to the higher number of serrations in dorsal and pectoral spines in C. flaveolus (see diagnosis), the serrations are well-developed (vs. weak developed) and sometimes bifid (Fig. 2b), whereas the new species present only simple serrations (Fig. 2a). Other useful feature to diagnose the two species is the length of the outer mental barbel, which is smaller in the new species, distant from anteroventral limit of gill opening (vs. large, reaching or slightly surpassing the anteroventral limit of gill opening in C. flaveolus). The general shape of the body is also useful to distinguish the new species from C. flaveolus, which possesses robust body (Fig. 4) while Corydoras lacrimostigmata possesses a slender body (Fig. 1).
The pelvic girdle conspicuously differs between the new species and C. flaveolus. The anterior internal process of the basipterygium is slender in the new species (Fig. 5a). Corydoras flaveolus presents the anterior internal process of the basipterygium thicker (Fig. 5b). Other remarkable feature is the distance between the external anterior process and the dorsal ischiac process of the basipterygium. In C. flaveolus these two processes can be very close to each other or even fused (Fig. 5b), while the new species displays these processes distant from each other in all examined specimens (Fig. 5a).
Even the color pattern of Corydoras lacrimostigmata presents some differences from C. flavelous. In the new species, the spots, when present, are restricted to the snout tip and, in some specimens, to the top of the head, while C. flaveolus presents spots from the snout tip to the region of dorsal-fin base. Also, the flank of C. flaveolus is densely mottled with black chromatophores and, in some specimens, the dorsolateral series of plates is almost completely dusky. Specimens of the new species possesses less mottled flank. The same is observed on dorsal and caudal fins, which are densely covered of spots and bars, respectively, whereas the new species presents just a few spots and bars.
dot. Origin of each caudal-fin lobe with black blotch. Caudal fin with one to three irregular black bars.
Color in life. Similar to preserved specimens. Yellowish ground color of body slightly light and dark stripe between corner of mouth and anterior margin of orbit more evident than in preserved specimens.

Distribution.
Corydoras lacrimostigmata is known from rio Ivaí basin, a tributary of the rio Paraná, in the State of Paraná, Brazil (Fig. 3).
Etymology. From the Latim, the epithet lacrĭma, meaning tear, plus stigmata, meaning marks (plural of stigma), make allusion to the diffuse dark stripe between corner of mouth and anterior margin of orbit and the drop-shaped dark blotch on the posterior portion of infraorbital 1, which seem to be tears. A noun in apposition.

Discussion
Corydoras lacrimostigmata have a very similar color pattern to C. cochui Myers & Weitzman, 1954, from the upper rio Araguaia basin, C. diphyes Axenrot & Kullander, 2003 from Monday and Acaray Rivers, C. garbei Ihering, 1911, from rio São Francisco basin, and mainly to C. flaveolus, from rio Piracicaba basin. Despite the great resemblance between these species, the new species can be clearly distinguished by osteological and morphological features. The presence of three nasal pores, an uncommon condition for the genus, distinguishes the new species from C. cochui and C. garbei which present two pores. In addition, C. garbei presents a very developed Some tectonic processes, allied to the properties of the local rocks, caused inflections on the ground, including the Ponta Grossa Arch, and also numerous waterfalls, like the São João and São Francisco falls, both higher than 50 m (Maack, 1981), which may have caused the isolation of some fish populations. However, it is important to note that knowledge of the fish fauna of the rio Ivaí basin is precarious because very few collections have been carried out there, mainly in its tributaries (see Galves et al., 2009: fig. 1). The description of Corydoras lacrimostigmata highlights the requirement of further sampling and studies at the rio Ivaí basin, a relatively large, yet poorly known tributary to the upper rio Paraná basin concerning its fish fauna.
Comparative material. A list of the comparative material is available in Britto (2003). In addition, the following material was examined: Argentina. In the description of C. diphyes and Otocinclus mimulus, Axenrot & Kullander (2003) commented about the mimetic relation between both species and another pairs of syntopic Corydoras and Otocinclus species: O. flexilis Cope, 1894 and C. paleatus (Jenyns, 1842), O. affinis Steindachner, 1877and C. nattereri Steindachner, 1877, and O. xakriaba Schaefer, 1997and C. garbei Ihering, 1911. The latter pair seems to evidence an uncommon case of mimetic association, since the shared similarity is perceived between adult specimens of O. xakriaba and juveniles of C. garbei (Axenrot & Kullander, 2003: 269-270). Corydoras lacrimostigmata seems to possess similar mimetic association with Characidium heirmostigmata Graça & Pavanelli, 2008. Both species were captured together in syntopy in the rio Barra Grande and in the rio Nestor (W. J. da Graça, pers. obs. on specimens of the rio Barra Grande). The resemblance is more evident in the color pattern. The two species have a midlateral series of small black or brownish blotches on flank, a small black dot in the middle of caudal-fin base, dorsal series of black or brownish blotches and a diffuse dark stripe between corner of mouth and anterior margin of orbit (Fig.  6). Furthermore, the new species present caudal-fin lobes with conspicuously rounded distal border, which is generally pointed in Corydoras (see Fig. 4), very similar to the caudal-fin lobes in Characidium heirmostigmata (see Fig. 1). Maier et al. (2008) presented a checklist of fish species in rio Barra Bonita, tributary to the rio Ivaí. Thirteen of the 31 listed species are possible new species, some of them included in the list of 50 possible new species from the upper rio Paraná basin mentioned by Langeani et al. (2007). However, some of the 13 species listed by Maier et al. (2008) were not included in Langeani et al. (2007), such as some potentially new Hypostomus species. Other example is C. heirmostigmata which was not listed in both studies.
The endemic species in the rio Ivaí basin can be attributed to some interesting geomorphological factors, mainly in its middle and upper regions, which are inserted into the Serra Geral (also known as Serra da Boa Esperança) as described by Maack (1981).