Integrative Taxonomy Reveals a New Species of Imparfinis (Siluriformes: Heptapteridae) from the Upper Xingu River Basin

is a genus of small catfishes with 21 valid species broadly distributed throughout the main river basins of the Neotropical region. Here, a new species of Imparfinis is described from the headwaters of the Rio Xingu. The new species is distinguished from its congeners by the presence of a wide dark stripe from snout tip to caudal peduncle sharply contrasting pale underside and aligned with dark stripe centered on dorsal portion of lower caudal-fin lobe, 11–12 gill rakers on the first ceratobranchial, 39 vertebrae, maxillary barbel surpassing vertical through dorsal-fin origin, and absence of short, flexible extension of the anteriormost pectoral, dorsal, and upper caudal-fin rays. In addition, assemble species by automatic partitioning (ASAP) and the Poisson tree processes model (bPTP) analyses support the validity of this new species. Our molecular phylogeny based on the cytochrome c oxidase subunit 1 mitochondrial gene (COI) corroborates the placement of the new species in Imparfinis and its close relationship with I. guttatus. Species delimitation in Imparfinis is discussed.

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Fig. 1.

Representatives of genus Imparfinis: (A) I. arceae, new species; (B) I. mirini; (C) I. lepturus; (D) I. minutus in lateral and dorsal views; (E) Imparfinis sp. “Lower Tocantins”; (F) Imparfinis sp. “Upper Tocantins”; (G) Imparfinis sp. “Peru”; (H) I. sp. UA; (I) Imparfinis cf. hasemani “Maroni.”

Fig. 2.

Maximum likelihood tree based on COI sequence data. Black nodes indicate >90% bootstrap values from 1,000 pseudoreplicates; gray nodes indicate support between 70% and 90% bootstrap values. Bars represent the molecular analysis used for species delimitation: bPTP (red) and asap (blue). UA = Upper Araguaia. See Data Accessibility for tree file.

Fig. 3.

Left column: Imparfinis arceae, holotype, MCP 55325, 47.9 mm SL. Right column: Imparfinis arceae, ANSP 187252, from top to bottom: 50.5 mm SL; 43.9 mm SL; 40.6 mm SL; 36.9 mm SL.

Fig. 4.

Radiograph image of Imparfinis arceae: (A) paratype, 50.5 mm SL; (B) holotype, 47.9 mm SL.

Fig. 5.

Geographic distribution of Imparfinis arceae. Black star = holotype. Red circles = paratype localities.

Fig. 6.

Affluent of Córrego das Flores, municipality of Querência/MT, 12°33′20.5″S, 52°16′16.1″W, habitat where the specimens of I. arceae were found. Photo: Martin I. Taylor.

Fig. 7.

Imparfinis cf. arceae (MZUSP 96332) from the Rio Curuá, a tributary to the Rio Iriri (Xingu Basin), 8°46′9″S, 54°57′2″W, 21 October 2007. Photographed live by Mark Sabaj.

Fig. 8.

Imparfinis hasemani. (Top) Syntype of Imparfinis hasemani, NMW 46093. (Middle) Illustration of Imparfinis hasemani that accompanied original description by Steindachner (1915: figs. 1–2). (Bottom) Radiograph image of the syntype NMW 46093.