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| Tridensimilis magnus Colares Canto, Datovo, Ohara, de Pinna & Ribeiro, 2026. |
Abstract
A new species of translucent catfish of the genus Tridensimilis is described from the upper and middle rio Tapajós basin, states of Pará and Mato Grosso, Brazil. In addition, we redefine the taxonomic limits of the genus Tridensimilis and present evidence that questions the current generic placement of Tridentopsis tocantinsi. The new species is distinguished from congeners by a set of morphological features, in combination: number of vertebrae, anal-fin rays, opercular and interopercular odontodes; eyes positioned laterally and oriented ventrally, slightly more visible in ventral than in dorsal view; and basipterygia fused at midline. Live specimens of the new species display ex situ atmospheric air capture at the water surface, resulting in the filling of the digestive cavity with air bubbles, a behavior recorded for the first time in any representative of Tridentinae. The new species is the largest currently known of the subfamily Tridentinae, with analyzed specimen reaching 34 mm of standard length. The new taxon likely increases the list of endemism in the rio Tapajós basin.
Keywords: Amazon basin; Behavior; Biodiversity; Conservation; Taxonomy
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| Live specimens of Tridensimilis magnus: UFOPA-I 1773, 29.0 mm SL (A) and INPA-ICT 62042, not mensured (B-D). Arrows indicate swallowed air bubbles in stomach and intestines. |
Tridensimilis magnus, new species
Diagnosis. Tridensimilis magnus differs from all other Tridentinae in having the largest body length, reaching 34 mm SL (vs. 27 mm in Tridens, 25 mm in Tridentopsis Myers, 1925, 17 mm in Miuroglanis Eigenmann & Eigenmann, 1889, 18 mm in Rhinotridens, and 23 mm in Tridensimilis). The new species is further distinguished from all tridentines, except Rhinotridensbritskii, by having 39–41 post-Weberian vertebrae (vs. 34–38 in Miuroglanis, Rhinotridens chromocaudatus, Tridentopsis and Tridensimilis, and 45–52 in Tridens). Tridensimilis magnus additionally differs from Tridensimilisvenezuelae and T. tocantinsi LaMonte, 1939,in having longer maxillary barbels that surpass the opercular odontophore (vs. not extending beyond pupil); externally visible rictal barbels reaching the base of interopercular odontophores (vs. rictal barbels not externally visible or reaching at most one-third of distance from their base to anterior margin of eyes); 7 or 8 dorsal-fin rays (vs. 8–11); and pelvic-fin base vertically aligned with the 13th or 14th vertebra (vs. with the 11th vertebra). The new species is additionally distinguished from T. tocantinsi in having 6 or 7 opercular odontodes (vs. 10); from T.venezuelae by having 7 or 8 interopercular odontodes (vs. 4–6).
Etymology. The specific epithet magnus derives from Latin meaning “large” or “great”, in allusion to the longer length of the species in comparison to its congeners, emphasizing one of the distinctive morphological traits that diagnose the species. An adjective.
André L. Colares Canto, Aléssio Datovo, Willian M. Ohara, Mário C. C. de Pinna and Frank Raynner V. Ribeiro. 2026. A New Species of Tridensimilis (Siluriformes: Trichomycteridae) from Tapajós Basin: the Largest translucent Catfish Species of Tridentinae. Neotropical Ichthyology. 24(02); DOI: doi.org/10.1590/1982-0224-2025-0209 [20 July 2026]
