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| Copionodon elysium de Pinna, Burger & Zanata, 2018 |
ABSTRACT
A new species of the copionodontine genus Copionodon is described from the upper reaches of a tributary to the rio Paraguaçu in the Diamantina Plateau, Bahia State, northeastern Brazil. This species represents the northernmost occurrence of the subfamily yet known. The new species can be readily recognized by its large eye without a free orbital rim. Other characters such as the entirely cartilaginous second hypobranchial, and the uniformly broad irregular midlateral dark band further diagnose the new taxon. Its particular combination of characters is superficially intermediate between Copionodon and Glaphyropoma. Detailed analysis, however, indicates that it forms a monophyletic group with species of Copionodon and therefore it should be included in that genus.
Key-words: Chapada Diamantina; Endemicity; New taxon; Rio Paraguaçu; Systematics; Taxonomy
Copionodon elysium, new species
Diagnosis. Distinguished from all other copionodontine catfishes by the large eye without a free orbital rim (Figs. 1, 2; vs. large eyes and free orbital rim in Copionodon spp. or with small eyes but without a free orbital rim in Glaphyropoma spp.). Also, uniquely diagnosed in the subfamily by the second hypobranchial entirely cartilaginous (Fig. 3; vs. presence of a conical ossification cap in the anterolateral corner of the second hypobranchial in other copionodontines) and the reduced or vestigial adipose fin in adults, resulting in a dorsal profile of the caudal peduncle almost straight (Fig. 1; vs. caudal peduncle dorsally convex as a result of the well-developed adipose fin). Further distinguished from congeners by the thin upper and lower lips, with lower lip not flattened ventrally, continuous and not split in two halves by medial depression (Fig. 2b; vs. broader lips and presence of median constriction on lower lip), mouth inferior, located close to anterior margin of snout (vs. mouth distinctly ventral, located posterior to anterior margin of snout), and by the posteriorly-positioned dorsal fin (predorsal distance 56.7-61.7 % of SL vs. 46.0-55.0 % of SL). The new species is also distinguished by its color pattern, with an uniformly broad midlateral dark (Fig. 1; vs. narrow dark band in C. pecten, somewhat broad and asymmetrical dark band in C. lianae, or absence of dark lateral band in remaining copionodontines). Copionodon elysium further differs from C. pecten by the smaller interopercular patch of odontodes, distant from lower lip anteriorly and not reaching opercular aperture (Fig. 2b; vs. interopercular patch of odontodes large, extending from near lower lip anteriorly to beyond pectoral-fin insertion posteriorly) and longer barbels, with maxillary barbel usually reaching pectoral-fin origin and rictal one extending beyond midlength of interopercular patch of odontodes (vs. maxillary barbel reaching posterior ¼ of length of interopercular patch of odontodes and rictal reaching anterior ¼ of length of interopercular patch of odontodes). From the species of Glaphyropoma, the new taxon further differs by a series of characters, including the broad hypobranchial (Fig. 3; vs. slender), the caudal fin bilobed (Fig. 1; vs. truncate), the toothed portion on dentary not reaching the coronoid process (Fig. 4; vs. reaching coronoid process), and the presence of asymmetrical spatulate teeth in jaws (Fig. 4; vs. all teeth symmetrically spatulate).
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| Collection site of Copionodon elysium, Riacho Águas Claras, near Morrão, Bahia, Brazil. |
Geographical distribution. Copionodon elysium is known exclusively from riacho Águas Claras, a stream of approximately 6 km, tributary of rio Mucugezinho, itself a tributary of rio Santo Antonio, upper rio Paraguaçu basin, Chapada Diamantina, Bahia State, Brazil (Fig. 6).
Ecological notes. The Águas Claras stream is perennial and torrential in the rainy season. Its headwaters are around 1000 m above sea level and it runs on the western slopes of the Sincorá Range, partly within the Chapada Diamantina National Park. The population has a patchy distribution in the stream, with individuals concentrating in certain stretches and entirely absent in others. Copionodon elysium was sampled in slow-flowing stretches over solid rock bottom or boulders, with riffles and shallow pools 10-30 centimeters deep and 1-3 meters wide (Fig. 7), with water transparent and tea-stained, though not to the same darkness as is typical in the Chapada Diamantina. Shallow pools have accumulations of plant debris along the margin. Marginal vegetation is typical “Campo Rupestre”, an herbaceous-shrub vegetation type that develops at elevations of about 900 m on sandstones and quartzite. Shrubs of Bonnetia stricta (Nees) Nees, Mart. (Bonnetiaceae) dominate the margins along the stretches sampled. The only other fish species collected with C. elysium was Astyanax sp.
The analysis of stomach contents of three specimens of C. elysium includes allochthonous and autochthonous items, composed mainly of aquatic insects (Trichoptera: larvae of Hydroptilidae and Hydropsychidae; Diptera: larvae of Simuliidae and Chironomidae; adult coleopterans; Plecoptera eggs), filamentous algae, and fragments of adult terrestrial insects (Hymenoptera: Formicidae), and numerous sand grains.
Considering the pristine condition of the type locality and its location inside an official preservation area, there are no evident threats to the survival of C. elysium, despite its narrowly endemic distribution and probably small population size.
Etymology. The specific epithet comes from the Greek elysium, in reference to the mythological Elysean Fields: a place or condition of ideal happiness; a state or place of perfect bliss. This alludes to the locality inhabited by the new species, a scenic pristine place (Fig. 7) shared with a single other fish species and no fish predators. A noun in apposition.
Mario de Pinna, Rafael Burger and Angela Maria Zanata. 2018. A New Species of Copionodon lacking a free orbital rim (Siluriformes: Trichomycteridae). Neotrop. ichthyol. 16(2); DOI: 10.1590/1982-0224-20170146
RESUMO: Uma nova espécie do gênero Copionodon, subfamília Copionodontinae, é descrita para o trecho superior de um tributário do Rio Paraguaçu na Chapada Diamantina, Estado da Bahia, nordeste do Brasil. Este registro representa a ocorrência mais ao norte de Copionodontinae até agora conhecido. A nova espécie pode ser facilmente reconhecida por ter olho grande sem margem orbital livre. Outras características como o segundo hipo-branquial inteiramente cartilaginoso e uma faixa escura lateral irregular de largura uniforme também servem para diagnosticar o táxon. A combinação particular de caracteres do novo táxon é superficialmente intermediária entre Copionodon e Glaphyropoma. Entretanto, uma análise mais detalhada indica que forma um grupo monofilético com Copionodon e portanto deve ser incluída neste gênero.
Palavras-chave: Chapada Diamantina; Endemicidade; Novo Táxon; Rio Paraguaçu; Sistemática; Taxonomia
