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| Characidium lilloi Terán, Méttola, Alonso, Montes, Méndez-López, Miranda, Aguilera & Mirande, 2026 |
Abstract
Using an integrative approach that combines molecular and morphological analyses, we describe Characidium lilloi, a new species from the Andean portion of the northwestern La Plata basin, specifically from the upper Bermejo and Juramento River basins in Argentina. Specimens were examined for morphometric, meristic, and osteological traits. Genetic analyses based on COI and CYTB sequences were conducted to infer its phylogenetic relationships. The new species is distinguished by a unique combination of morphological characters including an unscaled isthmus, absence of dark stripes or spots on fins, 7–13 regular transversal bars, 14 scales around the caudal peduncle, 35–37 scales in longitudinal series, and highly developed nasal flaps; and molecular evidence. Characidium lilloi, new species, was found to be closely related to C. fasciatum and C. gomesi and represents the first known member of the C2 Clade in the northwestern La Plata basin. Ecologically, C. lilloi, new species, inhabits fast-flowing mountain rivers within the Yungas and Chacoan. This discovery underscores the northwestern La Plata basin as a biogeographic hotspot of endemism and reinforces its importance as a high-priority area for freshwater conservation.
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| Lateral views of live paratypes of Characidium lilloi. CI-FML 8196, 36.8–49.1 mm SL, Argentina, El Rey National Park, Río Popayán. Scale bar = 1 cm. |
Characidium lilloi, new species
Etymology.—This species is named in honor of the Argentine naturalist Miguel Lillo (1862–1931), a pioneer who recognized the importance of public investment in science and education. In his commitment to advancing these fields, Lillo donated his personal assets before his death, ensuring the continuity of his legacy through several key institutions. These include the Facultad de Ciencias Naturales e Instituto Miguel Lillo, the Fundación Miguel Lillo, and the Unidad Ejecutora Lillo–CONICET, all of which have played significant roles in the development of science and education in Argentina. The specific name lilloi, thus, not only pays tribute to Lillo’s contributions but also honors the dedication of public workers in Argentina who promote and contribute to the progress of science, education, and technology.
Guillermo E. Terán, V. Ezequiel Méttola, Felipe Alonso, Martín M. Montes, Alejandro Méndez-López, Guido Miranda, Gastón Aguilera and J. Marcos Mirande. 2026. A New Species of Characidium (Characiformes: Crenuchidae) from the Northwestern La Plata Basin in Argentina. Ichthyology & Herpetology. 114(2):283-298 DOI: doi.org/10.1643/i2025064 [23 June 2026]
Utilizando un enfoque integrador que combina análisis moleculares y morfológicos, se describe Characidium lilloi, una nueva especie proveniente del sector andino del noroeste de la cuenca del Plata, específicamente de las cuencas altas de los ríos Bermejo y Juramento en Argentina. Los ejemplares fueron examinados en cuanto a caracteres morfométricos, merísticos y osteológicos. Se realizaron análisis genéticos basados en las secuencias de los genes mitocondriales COI y CYTB con el fin de inferir sus relaciones filogenéticas. La nueva especie se distingue por una combinación única de caracteres morfológicos incluyendo el istmo sin escamas, ausencia de bandas oscuras o manchas en las aletas, presencia de 7 a 13 barras transversales regulares, 14 escamas alrededor del pedúnculo caudal, 35 a 37 escamas en la serie longitudinal, y lóbulos nasales altamente desarrollados; y evidencia molecular. Characidium lilloi, nueva especie, se encuentra estrechamente relacionada con C. fasciatum y C. gomesi, y representa el primer miembro conocido del Clado C2 en el noroeste de la cuenca del Plata. Desde el punto de vista ecológico, C. lilloi, nueva especie, habita ríos de montaña de corriente rápida, dentro de las ecorregiones de las Yungas y el Chaco. Este hallazgo resalta al noroeste de la cuenca del Plata como un hotspot biogeográfico de endemismos, y refuerza su importancia como una región de alta prioridad para la conservación de ambientes dulceacuícolas.