Redescription of Astyanax multidens Eigenmann , 1908 ( Characiformes : Characidae ) , a small characid of the Brazilian Amazon

Astyanax multidens is redescribed based on syntypes and additional specimens from the rio Amazonas at Silves, Amazonas State and Óbidos, Pará State, and the rios Trombetas, Tapajós, Xingú, and Araguaia. Astyanax multidens is distinguished from congeners by the unique combination of five to seven maxillary teeth, 31 to 34 pored lateral-line scales, 20 to 23 branched analfin rays, and a dark triangular blotch restricted to the middle caudal-fin rays. Astyanax multidens was collected syntopically with Jupiaba paranatinga in the rio Tapajós basin and with Jupiaba cf. essequibensis in the rio Xingu basin, which have paired anteriorly oriented pelvic-fin spines, a antipredatory mechanism. Based on the external morphological similarity between Astyanax multidens and the two species of Jupiaba, their sympatric occurrence, and their distinct phylogenetic position, we interpret this a case of Batesian mimicry.


Introduction
The family Characidae is the fourth largest family of fishes in the World, with over 1.100 valid species, being smaller only than the freshwater families Cyprinidae, Cichlidae, and the mainly marine Gobiidae (Nelson, 2006;Eschmeyer & Fricke, 2012).Interestingly, contrary to these three families, the Characidae is much more geographically limited, being restricted to South America, from Texas (U.S.A.) to Argentina.The family is experiencing a high annual rate of species description, with 46 new species in 2010, despite the still prevalent poor knowledge about the taxonomy and interrelationships of species.Half of the species of the Characidae were listed as incertae sedis by Lima et al. (2003).Most of the larger genera, such as Astyanax Baird & Girard, Moenkhausia Eigenmann, Hyphessobryson Durbin, and Hemigrammus Gill, are now considered to be not monophyletic (Lima et al., 2003), with numerous species level problems.
Astyanax is primarily characterized by having two series of teeth on the premaxilla with the inner tooth row consisting of five teeth, complete lateral line, and caudal fin not covered by scales (Eigenmann, 1917;1921), but has been considered to be not monophyletic for over 40 years (Rosen, 1972;Weitzman & Fink, 1983;Weitzman & Malabarba, 1998;Lima et al., 2003).Furthermore, recent phylogenetic analyses based on molecular data, including only very few species (two or three in each study) have also demonstrated the nonmonophyletic condition of Astyanax (Calcagnotto et al., 2005;Javonillo et al., 2009;Oliveira et al., 2011).In a comprehensive phylogenetic analysis of the Characidae, Mirande (2010) recovered the species of Astyanax in three different monophyletic groups with A. latens Mirande, Aguilera & Azpelicueta closely related to two species of Hyphessobrycon (in the Hyphessobrycon luetkenii clade), A. paris Azpelicueta, Almirón & Casciotta the sister to a large characid clade, and Astyanax spp.(15 species) in what he termed Astyanax clade which also includes Hyphessobrycon anisitsi (Eigenmann), Markiana nigripinnis (Perugia), and Psellogrammus kennedyi (Eigenmann).Mirande's (2010) Astyanax clade is supported by a single non-exclusive synapomorphy: the presence of one or no maxillary teeth.
We recently collected specimens of a small-sized characid widely distributed in the rio Tapajós basin which proved to be Astyanax multidens Eigenmnann, 1908.This is a poorly known species described more than a century ago and only cited in fish catalogs, or as citations of samples from the rio Paraguay basin.The aim of the present contribution is to redescribe Astyanax multidens based on syntypes and recently collected specimens.

Color in alcohol.
Overall ground color yellowish.Opercular area silvery.Lips, anterior portion of maxilla, and dorsal portion of head with small dark chromatophores.Larger chromatophores on upper one-half of opercle.Scales of two or three dorsalmost longitudinal scale rows bordered by dark pigmentation.Humeral blotch conspicuous, vertically oriented, from one scale row ventral of, and three scale rows dorsal of lateral line, and over three scales horizontally.Lower half of humeral spot often interrupted by clear horizontal area.Clear area between humeral blotch and posterior pigmented area that fades longitudinally.Stripe extending over four or five longitudinal scale rows dorsal to lateral line, and from vertical through 7 th or 8 th lateral line scale to caudal peduncle.Dark pigmentation along horizontal septum, approximately from vertical through dorsal-fin origin to caudal peduncle.Clear area anterior to caudal-fin base.Pectoral, pelvic and adipose fins with scattered dark chromatophores.First unbranched dorsal-fin ray with dark chromatophores; remaining rays hyaline.Distal portion of interadial membranes of all dorsal-fin rays with scattered dark chromatophores.Anal fin with scattered small chromatophores.Chromatophores frequently concentrated at proximal and distal portions of interadial membranes.Caudal fin with somewhat and sometimes diffuse triangular blotch on middle rays.Anterior margin of blotch straight; posterior pointed.Caudal-fin lobes hyaline or with scattered dark chromatophores.
Color in life.Coloration in life similar to described above for preserved specimens, except for dorsal portion of iris red, distal portion of anteriormost rays of dorsal, pelvic and anal fins white, adipose fin red, and caudal fin with pale orange blotch immediately dorsal and ventral to dark median blotch (Fig. 4).
Sexual dimorphism.No sexually dimorphic modification was observed.

Remarks.
During the Thayer Expedition, James collected 40 specimens of small characids at Óbidos, which were kept in a single jar and catalogued as MCZ 20840.Eigenmann (1908Eigenmann ( , 1918Eigenmann ( , 1927) ) Eigenmann (1927) cited a single specimen (MCZ 20826, Fig. 1c) as "probably identical with" the type specimens of Astyanax multidens.Our examination confirm Eigenmann's (1927) suggestion that the aforementioned specimen is indeed conspecific with the syntypes of Astyanax multidens.
Examinations of the type series of Moenkhausia collettii deposited at the NMW revealed that part of the syntypes from Óbidos (NMW 57382, 5), is conspecific with Astyanax multidens.Astyanax multidens can be promptly distinguished from Moenkhausia collettii by having a the middle caudalfin rays dark (vs.middle caudal-fin rays hyaline), 5 to 7 maxillary teeth (vs. 1 to 3), scales restricted to the base of the caudal fin, along basal one-sixth of upper lobe and basal one-fourth of lower lobe (vs.along one-fourth of the upper lobe and half of the lower lobe) and by the absence of a black line on the analfin base (vs.presence).Since the type series of Moenkhausia collettii is composed of more than one species, a lectotype designation of that species is in need.However, this is beyond of the scope of the present contribution, as it should be done in a separate study about the taxonomy and distribution of M. collettii.Noteworthy to say that Steindachner (1882) described the maxilla as edentulous in the original description of M. collettii and also illustrated a specimen with middle caudal-fin rays hyaline, features not present in specimens of Astyanax multindes.Although Bertoni (1939) and Fowler (1948) mentioned Astyanax multidens for the upper rio Paraguay, their reports are doubtful since the extensive material analyzed from that drainage do not have any specimens of Astyanax multidens.Géry (1977: 426) also mentioned Astyanax multidens, referring it to his "Astyanax-paucidens group", which also includes other poorly known species such as A. scintillans Myers, 1928, A. guaporensis, A. guianensis, A. paucidens (Ulrey, 1894), A. gracilior Eigenmann, 1908, A. kennedyi Géry, 1964, and A. essequibensis Eigenmann, 1909 [=Jupiaba essequibensis].

Discussion
Astyanax multidens does not belong to Mirande's (2010) Astyanax clade for having five to seven maxillary teeth, and thus lacking the unique synapomorphy of that clade (i.e., none or one maxillary teeth).Based on external similarities, Astyanax multidens most closely resembles A. guaporensis and A. guianensis.The latter two species also possess somewhat diamond-shape body, two vertically oriented humeral blotch and no dark blotch on caudal peduncle, five or more teeth on maxilla, and relatively few pored scales on lateral line (33 to 36).
Specimens of Astyanax multidens were collected in sandy beaches in the rio Teles Pires and rio Jamanxim in syntopy with specimens of Jupiaba paranatinga Netto-Ferreira, Zanata, Birindelli & Sousa (Fig. 6a), and in sandy beaches of the rio Xingu in syntopy with Jupiaba cf.essequibensis Eigenmann (Fig. 6b).The three aforementioned species are very similar in coloration (e.g., dark marking on dorsal and anal fins), body size and shape.However, Astyanax multidens lack all the synapomorphic features of Jupiaba, including a modified elongate pelvic bone developed as an anteriorly oriented spine (Zanata, 1997), an antipredatory mechanism (Zanata et al., 2009).Therefore, given the external morphological similarity between the three species, their sympatric occurrence, and their distinct phylogenetic position (considering Jupiaba as monophyletic, following Zanata, 1997), we interpret this as a case of Batesian mimicry, comparable to other previously described (Zanata et al., 2009;Zanata & Ohara, 2009).

Fig. 5 .
Fig. 5. Distribution of Astyanax multidens in the rio Amazonas basin.White circle represent the type localities.

Table 1 .
Morphometric data of Astyanax multidens.SD for Standard Deviation.