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| Rhinotridens chromocaudatus Datovo, Ochoa, Vita, Presti, Ohara & de Pinna, 2023 |
Abstract
A new miniature tridentine catfish is described from the rio Purus drainage, Amazon basin, Brazil. It differs from all other tridentines in having several unique autapomorphies: conspicuous anteromedial protuberance in the snout; set of symphyseal premaxillary and dentary teeth inclined posteromedially; distal process of the hyomandibula directed anteriorly; rod-like orbitosphenoid ossified only ventral to the optic nerve; mesethmoid cornua inclined ventrolaterally; opercular and interopercular odontodophores separated by a large interspace; basipterygia fused sagittally; and conspicuous dark brown horizontal stripe in the middle of the caudal fin. The new taxon is hypothesized to be sister to the clade formed by Tridensimilis and Tridens. A detailed osteological description of the new taxon is provided based on X-ray microcomputed tomography (µCT-scans) data and on cleared and stained specimens. Our analysis also reveals that “Tridens” brevis, an enigmatic species that has been indecisively assigned to three different tridentine genera over the past 134 years, belongs to Tridentopsis.Consequently, Tridensimilis is a monotypic genus that currently includes only T. venezuelae.
Keywords: Freshwater; Loricarioidei; Ostariophysi; Systematics; Taxonomy
Rhinotridens, new genus
Type-species. Rhinotridens chromocaudatus, new species.
Diagnosis. Rhinotridens is distinguished from all other tridentine genera by the following unique autapomorphies: presence of a conspicuous anteromedial protuberance on the snout, with a length greater than 35% of its width (Fig. 1; vs. protuberance absent or limited to a discreet convexity with a length less than 18% of its width; see Baskin, 1973: fig. 66; Henschel et al., 2023: figs. 2, 8, 12, 13); set of symphyseal premaxillary and dentary teeth inclined posteromedially (Fig. 2; vs. not inclined, see Azpelicueta, 1990: figs. 2, 3; Henschel et al., 2023: fig. 9); rod-like orbitosphenoid ossified only ventral to the optic nerve (Fig. 3; vs. laminar bone ossified around the optic nerve, with a foramen for its exit, see Baskin, 1973: figs. 28, 29; Henschel et al., 2023: fig. 3); mesethmoid cornua inclined ventrolaterally (Fig. 4; vs. cornua horizontally straight); distal process of the hyomandibula directed anteriorly (Fig. 5; vs. posteriorly, see Baskin, 1973: fig. 51; Henschel et al., 2017: fig. 2g; Henschel et al., 2023: fig. 4); opercular and interopercular odontodophores separated by a large interspace, greater than the depth of the opercular patch (Fig. 5; vs. patches nearly juxtaposed, separated by a distance less than the depth of the opercular patch, see Baskin, 1973: fig. 51; Azpelicueta, 1990: fig. 4; Henschel et al., 2017: fig. 2g; Henschel et al., 2023: fig. 4); and basipterygia fused sagittally (Fig. 6; vs. separated).
Etymology. From rhino, latinized form of the Greek word rhinos (ῥινός), meaning nose or snout, and Tridens, the type genus of the subfamily. In allusion to the rostral protuberance of the new genus. An adjective.
Rhinotridens chromocaudatus, new species
Diagnosis. The new species differs from all other tridentines by having a conspicuous dark brown horizontal stripe in the middle of the caudal fin (Fig. 1). Ongoing studies indicate the existence of additional undescribed species of Rhinotridens that lack this caudal stripe (see Discussion). As a result, this character is preemptively proposed as autapomorphic for R. chromocaudatus rather than as a synapomorphy for the genus as a whole.
Etymology. From chroma, latinized form of the Greek word khrôma (χρῶμα), meaning color, and cauda, a Latin word meaning tail. In reference to the presence of the dark brown pigmentation in the middle of the caudal fin. An adjective.
Alessio Datovo, Luz Ochoa, George Vita, Paulo Presti, William M. Ohara and Mario C. C. de Pinna. 2023. A New Genus and Species of miniature tridentine Catfish from the Amazon Basin (Siluriformes: Trichomycteridae). Neotrop. ichthyol. 21(3); www.ni.bio.br/1982-0224-2023-0076
