Abstract
ABSTRACT A new species in the serrasalmid genus Myloplus is described from the middle Mazaruni River, Essequibo River basin, Guyana. The new species is similar to Myleus pacu and Myloplus planquettei in its silver to purplish black coloration and its overall morphology, and has a putative syntopic distribution with those species. The new species is, however, readily distinguishable from the other two by meristic counts of the unpaired fins and by differences in color pattern, primarily in males. Additionally, we provide comments on Myleus pacu and other species that have been confounded under that name.
Highlights
The diversity of the Serrasalmidae “pacu” genus Myloplus Gill, 1896, with currently recognized species, is second only to the most speciose herbivores of the genus Metynnis Cope, 1878, which contains named species (Ota et al, 2016; Fricke et al, 2019)
Males and females of Myloplus taphorni are readily distinguished by the coloration of the males, which consist of striking purplish silver flanks with conspicuous black overtones composed by scales intensely pigmented and often with a metallic green sheen, whereas females are mainly bluish silver without any evident pigmentation or markings (Fig. 3)
The presence of evident marks on males of Myloplus taphorni is reminiscent of the congeners M. asterias and M. planquettei, the coloration pattern exhibited by males M. taphorni is unique in having many scales fully pigmented in black forming a vermiculated pattern around a distinct silvery or yellowish region that may present black spotting on and below the lateral line (Fig. 2)
Summary
The diversity of the Serrasalmidae “pacu” genus Myloplus Gill, 1896, with currently recognized species, is second only to the most speciose herbivores of the genus Metynnis Cope, 1878, which contains named species (Ota et al, 2016; Fricke et al, 2019). Outside the Amazon basin, Myloplus is diverse in the coastal drainages of the Guiana Shield, encompassing the Orinoco, Essequibo, and Atlantic flowing river basins of the Guianas, which harbor ten recognized species (Fricke et al, 2019): Myloplus asterias (Müller, Troschel, 1844), Myloplus arnoldi Ahl, 1936, Myloplus lobatus (Valenciennes, 1850), Myloplus planquettei Jégu, Keith, Le Bail, 2003, Myloplus rhomboidalis (Cuvier, 1818), Myloplus rubripinnis (Müller, Troschel, 1844), Myloplus schomburgkii (Jardine, 1841), Myloplus ternetzi (Norman, 1929), Myloplus torquatus (Kner, 1858), and Myloplus tumukumak Andrade, Jégu, Gama, 2018 Despite this diversity and of relatively detailed historical sampling of their ichthyological diversity (e.g., Eigenmann, 1912; Géry, 1972), tributaries of the Guiana Shield continue to reveal previously undescribed species of Myloplus. We report and describe a previously unknown species of Myloplus from the Mazaruni River, a tributary of the Essequibo River basin in Guyana This species was initially identified as Myleus pacu (Jardine, 1841) because of its silver to purplish black coloration and its supposedly syntopic distribution with that species. We provide some comments on characters distinguishing Myleus pacu and other species that have been confounded under that name
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