A new species of Corydoras LAcépède ( siLuriformes : cALLichthyidAe ) from the rio tApAjós bAsin And its phyLogenetic impLicAtions

A new species of Corydoras is described from tributaries of the rio Arinos, rio Teles Pires and rio Preto, all in the rio Tapajós basin. The new species is a member of a group that includes 36 species with spots on the body. Within this group, the new species can be readily distinguished by having a smaller dorsal-fin spine than the first three subsequent soft dorsal-fin rays; pectoral, pelvic and anal fins hyaline; dorsal-fin interradial membrane hyaline; rounded spots on trunk restricted to dorsolateral body plates and dorsal portion of ventrolateral body plates, not reaching the base of pelvic and anal fins. The new species can be further distinguished from Corydoras xinguensis by having spots with diffuse edges, and from all other species of spotted Corydoras except C. multimaculatus, by the absence of ventral platelets. A phylogenetic analysis recovered the new species plus Corydoras metae and C. araguaiensis in a clade sharing the presence of a pointed process on the maxilla for insertion of the retractor tentaculi muscle. In addition, the presence in the new species of an elongated anterior portion of the mesethmoid and a triangular uncinate process of the epibranchial 3 suggests a close relationship with Corydoras metae. Key-Words: Corydoradinae; Neotropical; Phylogeny; Taxonomy; Biodiversity.


IntroductIon
Corydoras Lacépède is the most diversified catfish genus, currently including more than 160 valid species (Eschmeyer, 2013).The species of Corydoras are widely distributed throughout cis-Andean South America in habitats such as shallow marginal areas of rivers, pools, and smaller tributaries (Reis, 2003).Despite the huge diversity of shapes and color patterns among the species of Corydoras, the limits and definitions of a large amount of species are still unknown (Gosline, 1940;Nijssen & Isbrücker, 1980, 1986;Reis, 1998Reis, , 2003;;Britto, 2003).
Two species of Corydoras were originally described from the rio Tapajós basin: C. bifasciatus Nijssen 1972and C. ornatus Nijssen & Isbrücker 1976. Corydoras aeneus (Gill, 1858) and C. splendens (Castelnau, 1855) were also recorded from the same basin (Britto et al., 2007), and there are many other forms yet to be described (Fuller & Evers, 2005).Nijssen (1970) proposed an assembly of Corydoras species, the "C.punctatus-group", grouping all species with spots scattered over the body, and divided into six subgroups according to the following features: (a) dark spot on the upper part of the dorsal fin; (b) dark mask across the eye; (c) long snout; (d) relatively elongate body; (e) deep body; and (f ) relatively long dorsal-fin spine.The author also mentioned that the spotted Corydoras group has a large range of distribution, with records from the northern to central Neotropical region, and that it includes almost 35% of all described species.The present study will focus on specimens of the Nijssen's (1970)

MAterIAls And Methods
Morphometric and meristic data were taken following Reis (1997), except for the length of the anal-fin spine, which is absent in all members of Corydoradinae.Length of the ossified portion of the pectoral-fin spine was measured from the point of articulation of the spine to the pectoral girdle to the distal tip of the spine (Reis, 1997).Measurements were taken with calipers to the nearest 0.1 mm.Teeth and vertebral counts were made from cleared-andstained (cs) specimens prepared according to Taylor & Van Dyke (1985).Vertebral counts include 27-30 vertebrae, with the compound caudal central (preural 1 + ural 1) counted as a single element.Lateral plate counts include all dorsolateral and ventrolateral plates, except for the small, irregular plates on the caudal peduncle.Throughout the description, the numbers in parentheses following each count represent the total number of specimens with that value, and an asterisk indicates data for the holotype.No-menclature of latero-sensory canals follows Schaefer & Aquino (2000), and that of preopercular pores follows Schaefer (1988).Osteological terminology follows Reis (1998), except that parieto-supraoccipital is used instead of supraoccipital (Arratia & Gayet, 1995), and compound pterotic instead of pterotic-supracleithrum (Aquino & Schaefer, 2002).Homology of barbels follows Britto & Lima (2003).Institutional abbreviations follow Sabaj Pérez (2010).
Phylogenetic analysis was performed using the morphological character data matrix exactly as published by Britto (2003) with the addition of the new taxon.The analysis was undertaken using T.N.T. software (Goloboff et al., 2008) via a traditional heuristic search performed using the stepwise addition algorithm associated with tree bisection reconnection in a total of 10,000 samples.Attributes of connectivity and ambiguity among character-states were treated in the same way as in Britto (2003).Posterior area of mesethmoid, frontal, sphenotic, compound pterotic, and parieto-supraoccipital visible externally, all covered by thin layer of skin and bearing minute scattered odontodes.Frontal fontanel elongate, ellipsoid, covered by thin layer of skin; posterior portion extending into parieto-supraoccipital.Nasal slender, curved laterally, mesial border contacting frontal.Frontal rectangular; anterior expansion in contact with nasal bone, posterior portion contacting sphenotic and parieto-supraoccipital.Sphenotic trapezoid in shape, contacting parieto-supraoccipital dorsally, compound pterotic posteriorly, second infraorbital ventrally.Compound pterotic roughly pipe-shaped, with posterior expansion contacting first lateral-line ossicle.Ventral margin of compound pterotic contacting opercle and cleithrum.Parietosupraoccipital quadrangular with posterior expansion notched at its tip, sutured with nuchal plate.

Corydoras apiaka
Two infraorbital bones, externally visible, covered by thin layer of skin.First infraorbital with anterior expansion.Second infraorbital bone contacting only sphenotic posteriorly.Opercle exposed, slender in shape, with smooth free border.Preopercle externally visible, slender and covered by thin layer of skin.
Trunk lateral line with three laterosensory canals; two anteriormost canals reduced to small ossicles.Last lateral-line canal encased in second dorsolateral body plate.Lateral-line canal entering neurocrani-um through compound pterotic, splitting into three branches before entering sphenotic: pterotic and preoperculomandibular, each with single pore.Sensory canal continuing through compound pterotic, entering sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, the other branch entering frontal through supraorbital canal.Supraorbital canal not branched, running through nasal bone.Epiphyseal pore opening at supraorbital main canal.Nasal canal with single opening at each end.Infraorbital canal running through entire second infraorbital, extending to infraorbital 1 and opening into three pores.Preoperculomandibular branch giving rise to preoperculomandibular canal, which runs through entire preopercle with three openings, leading to pores 3, 4, and 5, respectively.
Color in alcohol: Ground coloration of head light brown to brown, light brown ventrally.Interorbital to supraoccipital region darker than snout, anterior and posterior margins of the eye to opercle.Several small irregular chromatophores scattered over snout to parieto-supraoccipital. Chromatophores less concentrated over lower anterior and posterior margins on opercle and superior surfaces.Mental barbels dark brown, remaining barbels yellowish light brown.
Distribution: Corydoras apiaka is only known from tributaries of the rio Arinos, rio Teles Pires and rio Preto, clearwater tributaries of the upper rio Tapajós in Mato Grosso State,Brazil (Figs. 3,4).
Habitat and ecological notes: Corydoras apiaka was mostly found in lotic habitats in the rio Arinos and its tributaries.The rio Arinos has a muddy-brown color, with soft bottom of clay and sand.Most of the specimens were captured in the small forest streams of black or clear water, or in marginal ponds.

Etymology:
The specific name apiaka is treated as a noun in apposition and is named for the indigenous tribe Apiaká (means "people" in Tupi language), which originally occupied the middle and lower rio Arinos, lower rio Juruena, but is nowadays restricted to the lower rio Juruena (Menéndez, 1992).The tribe is known for facial tattoos and bravery in battles, as well as by anthropophagic rites after fights (Castelnau, 1850).

dIscussIon
All evidence assigns the non-monophyly of a spotted group of Corydoras.A recent published study about mimetic lineages in Corydoras performed by Alexandrou et al. (2011) shows relationships and patterns among co-mimics of certain regions.The authors pointed out that those sympatric co-mimics are more similar in coloration than those in allopatry.The test suggested a highly significant relationship between color pattern and geographical distribution.The authors identified 52 species belonging to 24 different mimicry rings, combining phylogenetic analysis and geographic distribution, each composed of two or three species.The co-mimic rings are composed of different evolutionary lineages corroborating Britto's (2003) hypothesis that color pattern is convergent and recovers weak phylogenetic signal.The new species, Corydoras apiaka (not included in the analysis) is the only described spotted Corydoras from Tapajós basin; another three described species from same basin (C.aeneus, C. bifasciatus and C. ornatus) have no spotted pattern.Yet many Corydoras morphotypes are still undescribed and demand taxonomic review (e.g., Fuller & Evers, 2005:280-361).
We agree with Britto's (2003) and Alexandrou et al. (2011) hypothesis that go against Nijssen's (1970) division of Corydoras into eight groups, one of them being the "punctatus-group" represented by the spotted Corydoras.The highly homoplastic spotted color patterns serve as evidence for the complexity of the evolution in the genus.
subgroups (a) and (e), plus Corydoras araguaiensis and C. haraldschultzi.Recent material sampled from tributaries of rio Teles Pires, rio Arinos and rio Preto revealed a spotted Corydoras, somewhat resembling species like C. albolineatus Knaack, C. maculifer Nijssen & Isbrücker, C. multimaculatus Steindachner, C. polystictus Regan and C. xinguensis Nijssen.Examination of the material revealed that this is a new species of Corydoras, which is described herein.

tAble 1 :
Morphometric data for Corydoras apiaka.Espíndola, V.C. et al: A new species of Corydoras from Rio Tapajós fin spine; straight to slightly concave from that point to caudal-fin base.Ventral profile of body straight from isthmus to pelvic-fin origin, slightly convex from that point to anal-fin origin.Profile slightly concave from first anal-fin ray to caudal-fin base.Body roughly triangular in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin.Eye round, dorsolateral on head; orbit delimited dorsally by frontal and sphenotic, ventrally by infraorbitals.Anterior and posterior nares close to each other and only separated by flap of skin.Anterior naris tubular.Posterior naris close to anterodorsal margin of orbit, separated from orbit by distance slightly smaller than naris diameter.Mouth small, subterminal, width nearly equal to bony orbit diameter.Maxillary barbel not reaching anteroventral limit of gill opening.Length of maxillary barbel nearly equal to that of outer mental barbel.Inner mental barbel fleshy.Small rounded papillae covering entire surface of all barbels, upper and lower lips, and isthmus.Gill membranes united to isthmus.Four branchiostegal rays covered by thin layer of skin; two distal branchiostegal rays united at their tips by branchiostegal cartilage.Teeth on upper pharyngeal tooth plate 46(1), and on fifth ceratobranchial 45(1).