REVISION OF THE NEOTROPICAL FISH GENUS METYNNIS COPE, 1878 (CHARACIFORMES, SERRASALMIDAE)
The taxonomic relationships within the neotropical characiform genus Metynnis Cope, 1878 (common name: Silverdollars) are absolutely unsatisfactory today. Ahl (1924, 1925, 1927, 1931) distinguished 24 taxa. Gosline (1951) reduced the number of valid species to six. Ahl and Gosline have not investigated enough the type-specimens of the earlier described species. Moreover, they did not have enough material available in order to estimate the variability of each species. The main part of the material of Ahl has no exact locality. The type-specimens of M. goeldii Eigenmann, 1903, M. orinocensis (Steindachner, 1908) and M. fasciatus Ahl, 1931 were lost at that time. Metynnis unimaculatus Steindachner, 1908 is a junior-synonym of Mylossoma duriventris (Cuvier, 1818). A redescription of the type-specimens was the first step of a revision of the whole genus Metynnis (Zarske & Géry, 1999). All nominal taxa were described and a type-specimen or topotypical specimen was figured for each of them. Metynnis altidorsalisIn some cases topotypical material is used for the proper characterization of the species. The following species were considered as valid: M. hypsauchen (Müller & Troschel, 1844), M. maculatus (Kner, 1858), M. lippincottianus (Cope, 1870), M. luna Cope, 1878, M. mola Eigenmann & Kennedy, 1903, M. orinocensis (Steindachner, 1908), M. guaporensis Eigenmann, 1915, M. altidorsalis Ahl, 1924, M. argenteus Ahl, 1924, M. otuquensis Ahl, 1924 and M. fasciatus Ahl, 1931. A lectotype is designated for M. maculatus (Kner, 1858), M. orbicularis (Steindachner, 1908) and M. ehrhardti Ahl, 1927.
In a next step two new species were described and a syntype of M. goeldii Eigenmann, 1903 was re-discovered. Metynnis longipinnis Zarske & Géry, 2008 from the río Casiquiare drainage in Venezuela is closely related to Metynnis hypsauchen (Müller & Troschel, 1844) according to its features (1) high number of gill-rakers, (2) long adipose fin, (3) deep body, (4) short head and (5) long occipitale and is clearly defined because of (1) the high number of serrae (36–37 vs. 27–32 of M. hypsauchen), (2) the small scales (91–93 vs. about 75–83), (3) uniformly silver colouration and (4) the extremely elongated dorsal fin and anal fin. From Metynnis altidorsalis Ahl, 1924 Metynnis longipinnis is clearly differentiated by its (1) number of gill-rakers (30–33 vs. 20–25 for M. altidorsalis), (2) the number of branched anal rays (37–40 vs. 32–37 for M. altidorsalis), (3) the number of serrae (36–37 vs. 29–35 for M. altidorsalis) and (4) the length of the occipitale (18.94–20.78 % SL vs. 11.7–15.6 for M. altidorsalis). Further more, M. longipinnis has a longer adipose fin (20.00–20.78 % SL vs. 11.8–16.2 for M. altidorsalis) and an elongation of the rays of dorsal and anal fin (vs. not elongated for M. altidorsalis). M. luna Cope, 1878, M. orinocensis (Steindachner, 1908) and M. guaporensis Eigenmann, 1915 are differentiated by its higher number of gill-rakers and larger head length. M. lippincottianus (Cope, 1870) has a completely different colouration.Metynnis polystictus
The next step includes a re-description of all valid species and a phylogenetic analyse of the genus.