Introduction <p>To deepen the knowledge of monogenoids associated with Amazonian fish, studies focused on description, identification and analysis are sought. In this way, the data on the parasitic fauna focused on this group of parasites can be kept up to date. Based on the above, the main objective of this research was to identify new species of monogenoids in the gills of <i>M. asterias</i> acquired in the Santa Clara Market, located in the lower area of Nanay, Loreto-Peru.</p> Materials and methods <p>Thirty specimens of <i>M. asterias</i> were acquired in the “Santa Clara” Market, in the city of Iquitos, Loreto-Peru. According to fishermen, specimens were captured in the Nanay River. Samples were collected between August 2024 and February 2025 and analyzed in the “Laboratorio de Parasitología y Sanidad Acuícola” from “Instituto de Investigaciones de la Amazonía Peruana” (IIAP) in Iquitos, Loreto-Peru.</p> Results <p>A new species of Monogenoidea was discovered parasitizing the gills of <i>M. asterias. Anacanthorus santaclarae</i> n. sp. is characterized by presenting a MCO as a straight grooved tube with a flared base, presenting a thin elongated expansion with a curved claw-shaped termination in its distal part; a long accessory piece, not articulated with the MCO base, presented as a rod in the form of a can opener.</p> Conclusions <p>This is the first data on the parasites of <i>M</i>. <i>asterias</i>. <i>Anacanthorus santaclarae</i> n. sp. is the eighth documented species of the genus in Peru.</p>