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<p><i>Pseudacanthicus nyktos</i> is a recently described loricariid catfish previously considered restricted to the lower Xingu River basin in the eastern Brazilian Amazon. Herein, we report new records from the Turiaçu River basin, Maranhão State, northeastern Brazil, supported by morphological and molecular evidence. Additional records were obtained through the reanalysis of COI sequences available in public databases and the examination of museum specimens previously identified as <i>Pseudacanthicus</i> sp. Molecular analyses revealed low genetic divergence (K2P = 0.47%) relative to a paratype, and all examined specimens were recovered within the same clade in the maximum likelihood analysis. These records expand the known distribution of <i>P</i>. <i>nyktos</i> to four hydrographic systems in the eastern Amazon and increase its estimated Extent of Occurrence (EOO) from 340,733 km<sup>2</sup> to 366,197.445 km<sup>2</sup>. Despite the broad EOO, the species still exhibits a comparatively low Area of Occupancy (AOO), indicating a sparse and diffuse distribution associated with specialized habitats. Our results suggest that the apparently disjunct distribution of <i>P</i>. <i>nyktos</i> likely reflects historical sampling limitations rather than a truly restricted geographic range.</p>

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Morphological and molecular evidence of the armored catfish Pseudacanthicus nyktos Lopes, Sousa & Chamon, 2024 (Siluriformes: Loricariidae) reveal a broad and disjunct distribution in the eastern Brazilian Amazon

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  • 发表日期：

    2026年7月20日

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  • Rafael F. Oliveira,
  • Lucas O. Vieira,
  • Lucas F. P. Ramos,
  • Antonio F. G. Bezerra,
  • Claudio Oliveira,
  • Felipe P. Ottoni

摘要

Pseudacanthicus nyktos is a recently described loricariid catfish previously considered restricted to the lower Xingu River basin in the eastern Brazilian Amazon. Herein, we report new records from the Turiaçu River basin, Maranhão State, northeastern Brazil, supported by morphological and molecular evidence. Additional records were obtained through the reanalysis of COI sequences available in public databases and the examination of museum specimens previously identified as Pseudacanthicus sp. Molecular analyses revealed low genetic divergence (K2P = 0.47%) relative to a paratype, and all examined specimens were recovered within the same clade in the maximum likelihood analysis. These records expand the known distribution of P. nyktos to four hydrographic systems in the eastern Amazon and increase its estimated Extent of Occurrence (EOO) from 340,733 km2 to 366,197.445 km2. Despite the broad EOO, the species still exhibits a comparatively low Area of Occupancy (AOO), indicating a sparse and diffuse distribution associated with specialized habitats. Our results suggest that the apparently disjunct distribution of P. nyktos likely reflects historical sampling limitations rather than a truly restricted geographic range.