Astyanax orthodus Eigenmann, 1907

Ruiz-C, Raquel I., Román-Valencia, César, Taphorn, Donald C., Buckup, Paulo A. & Ortega, Hernán, 2018, Revision of the Astyanax orthodus species-group (Teleostei: Characidae) with descriptions of three new species, European Journal of Taxonomy 402, pp. 1-45 : 4-6

Astyanax orthodus Eigenmann, 1907 species-group

Some species of Astyanax exhibit a horizontally elongate oval humeral spot with sharp, well delimited margins, which is bordered anteriorly and posteriorly by light regions mostly devoid of melanophores ( bimaculatus group). In this study we have observed that the different layers of pigment that form the humeral spot(s), have differing degrees of development and structure that are independent of each other ( Fig. 1 ). We found brown melanophores distributed in a thin superficial layer of the epithelium (Layer 1, Fig. 1 ) and another deeper layer that consists of dark melanophores (Layer 2, Fig. 1 ). In some species with a horizontally ovate humeral spot there may be subtle variation in this character, but they retain the basic humeral pigmentation pattern, namely, the pigment model of the humeral spot described for the orthodus group follows the general pattern of the bimaculatus group, however, in the orthodus group the humeral spot has four vertices that give it the shape of a polygon.

Key to the species of the Astyanax orthodus species-group

1. Predorsal midline with a continuous series of scales covering more than three quarters of the distance between the posterior tip of supraoccipital spine and dorsal-fin origin … 2

– Predorsal midline irregularly scaled, with isolated scales or short series of medial scales alternating with scales that extend to or over the dorsal midline from the sides, especially along the posterior-most portion of the predorsal midline ……………………………………………… 3

2. Caudal-peduncle spot restricted to the caudal fin and adjacent caudal peduncle ………………… 4

– Caudal-peduncle spot not restricted to the caudal fin and adjacent caudal peduncle, extended anteriorly as a continuous dark line or stripe on side of body ………………………………………………… 5

3. Caudal-peduncle spot short, not extending anteriorly to a vertical through the posterior tip of the adipose fin; body with reticulate pattern from the dorsum to the pelvic region ……………………… ………………………………… A. yariguies ( Torres-Mejía et al., 2012) (Magdalena River Basin)

– Caudal-peduncle spot long, extending anteriorly to or beyond a vertical through the posterior tip of the adipose fin; body with alternating light and dark horizontal wavy stripes ………………… ………………………………………………… A. superbus Myers, 1942 (Orinoco River Basin)

4. Caudal-peduncle spot restricted to the midlateral axis of the body, not extending on to the dorsal and ventral margins of bases of caudal-fin rays …………………………………………………… ………………… A. orthodus Eigenmann, 1907 ( Atrato River Basin, Caribbean Coast of Colombia)

– Caudal-peduncle spot extending on to the dorsal and ventral margins of the caudal- peduncle and the bases of caudal-fin rays …………… A. embera sp. nov. ( Patía River Basin, Pacific Coast of Colombia)

5. Caudal-peduncle spot extending anteriorly as a dark line reaching second humeral spot.…….. A. villwocki Zarske & Géry, 1999 (Ucayali, Beni and Mamoré River drainages, Amazon River Basin)

– Caudal-peduncle spot not extending anteriorly beyond vertical through the anal-fin origin ……… 6

6. Chevrons overlying lateral stripe short, their extensions not extending vertically from dorsal and ventral tips, occupying up to two series of scales above and below vertex of chevron; caudalpeduncle spot inconspicuous ……… A. gandhiae sp. nov. (Cenepa River drainage, upper Amazon)

– Chevrons overlying lateral stripe extended vertically by prolongations from dorsal and ventral tips over three horizontal rows of scales; caudal-peduncle spot conspicuous …………………… 7

7. Teeth present along two-thirds of the length of the maxilla ……………………………………… ……………………………………… A. bopiensis nom. nov. (Upper Madeira River drainage).

– Less than two-thirds of the length of the maxilla with teeth ……………………………………… 8

8. Lateral line with 43 or fewer scales ………………………………………………………………… ……………………… A. boliviensis sp. nov. (upper Madeira River drainage, Amazon River Basin)

– Lateral line with 44 or more scales …… A. moorii ( Boulenger, 1892) comb. nov. (Upper Paraguay)

Figures

Fig.1.A.DistributionofpigmentinthehumeralregionofAstyanaxspecies.B.A.bimaculatus(Linnaeus, 1758).C.A.caucanus(Steindachner,1879).D.A.mexicanus(DeFilippi,1853).E.A.courensisBertaco, Carvalho & Jerep, 2010 (modified from Bertaco et al. 2010). The anterior humeral spot consists of two overlapping layers of pigment identified by numbers 1 and 2 (see Román-Valencia et al. 2015: fig. 1): 1. Diffuse vertical bar. 2. Horizontal spot with concentrated pigments.