Imparfinis lepturus, Silva & Reia & Morimoto & Benine & Oliveira, 2023

Silva, Gabriel S. C., Reia, Lais, Morimoto, César K., Benine, Ricardo C. & Oliveira, Claudio, 2023, Integrative taxonomy of Imparfinis (Siluriformes, Heptapteridae) from the Upper Paraná River basin, Brazil, with description of a new species, Zootaxa 5249 (3), pp. 357-377 : 365-367

Imparfinis lepturus , new species

( Fig. 3 ; Table 4 )

urn:lsid:zoobank.org:act:057B59BB-CADB-4EEF-9F44-6ED11BC85520

Holotype. MZUSP 127602 , 44.9 mm SL, Brazil, Goiás, Aporé, Upper Paraná River basin, rio Corrente , 18°30’50.7”S 52°05’46.4”W, 15 Jul 2022, J. Crispim, L. Reia, G.S.C. Silva.

Paratypes. Brazil, Goiás, Aporé: LBP 25732, 16, 22.6−44.1 mm SL, 1 c&s (39.5 mm SL), Upper Paraná River basin, rio Corrente , 18°30’50.7”S 52°05’46.4”W, 28 Nov 2017, R. Devidé, B. Melo, C. Araya, G.S.C. Silva. LBP 32018, 12, 31.9−51.3 mm SL, 2 c&s (30.9−39.3 mm), same data as the holotype .

Diagnosis. Imparfinis lepturus differs from its congeners by having a mottled colored body, with concentrated chromatophores forming patches of black pigmentation ( Fig. 3 and 6 ) (vs. uniformly counter-shaded). Additionally, the new species differs from trans-Andean species by absence of a short extension of the pectoral, dorsal, and upper caudal-fin rays (vs. presence in I. usmai and I. nemacheir ), by having six gill rakers on the first ceratobranchial (vs. 10-11 in I. spurrelii ), 38 vertebrae (vs. 39−40 in I. usmai , 42 in I. lineatus , 42−43 in I. timana , 45 in I. spurrellii ). The new species differs from Amazon species by having 38 vertebrae (vs. 39−40 in I. munduruku , 40 in I. hasemani , 41 in I. cochabambae , 43−44 in I. longicauda ), by having six gill rackers on the first ceratobranchial (vs. 15 in I. cochabambae ), by absence of a short extension of the pectoral, dorsal, and upper caudal-fin rays (vs. present in I. guttatus ). The new species differs from I. piJpersi from Sipaliwini River and from I. minutus from S„o Francisco River by having longer maxillary barbel, reaching pelvic-fin origin (vs. not surpassing distal tip of adpressed pectoral fin), from I. minutus from S„o Francisco River by having 38 vertebrae (vs. 41), from I. mishky from Uruguai and lower Paraná basins by having 38 vertebrae (vs. 41), six gill rackers on first ceratobranchial (vs. nine), and maxillary barbel only reaching pelvic-fin origin (vs. surpassing pelvic-fin origin). Finally, the new species differs from its congeners from the Upper Paraná basin by having three irregular rows of teeth on premaxilla (vs. 5-6 in I. mirini , I. piperatus , and I. schubarti ); by having 38 vertebrae (vs. 39−40 in I. piperatus ; 40−41 in I. schubarti ), by having six gill rackers on first ceratobranchial (vs. 7−8 in I. mirini and 11 in I. schubarti ), a greater eye diameter 21.3−26.3% of HL (vs. 11.8−19.9% in I. mirini ), by smaller caudal peduncle depth 6.6−7.6% of SL (vs. 8.0−12.2% in I. mirini ; 10.0−12.3% of SL in I. schubarti ), by having the first dorsal-fin ray shorter than the second (vs. longer or approximately of same length that second ray in I. schubarti ), by having the lower caudal-fin lobe darker (vs. both lobes hyaline in I. mirini and I. piperatus ), and by absence of dark strip along flank (vs. presence of conspicuous longitudinal dark stripe in I. schubarti ).

Description. Morphometric data are summarized in Table 4 . Head slightly convex in lateral view. Snout short and rounded in dorsal view. Lateral profile of head slightly convex from snout tip to occipital region. Eyes large and elliptical, dorsolaterally positioned, just anterior to midpoint of head. Mouth subterminal. Upper jaw longer than lower jaw. Premaxilla and dentary with three irregular rows of small conic teeth. Maxillary barbel reaching posterior end of dorsal-fin base, when outstretched. Outer mental barbel longer than inner barbel. Outer mental barbel reaching posterior end of pectoral-fin base when outstretched. Inner mental barbel reaching the origin of pectoral-fin base when outstretched. Branchiostegal membrane free, supported by seven rays and joined to isthmus only at anteriormost point. Six gill rakers along anterior margin of first ceratobranchial.

Greatest body width at cleithral region, progressively narrowing anteriorly towards snout tip and posteriorly towards caudal fin. In lateral view, body depressed and convex in shape from end of head to dorsal-fin origin; slightly concave from dorsal-fin origin to adipose-fin origin; straight from adipose-fin origin to caudal peduncle. In lateral view, ventral profile straight and descending from snout tip to opercular region; slightly convex from opercular region to pelvic-fin origin; straight from that point to anal-fin origin; slightly concave from that point to origin of lower procurrent caudal-fin rays. Precaudal vertebrae 12 (seven supporting pleural ribs) and caudal vertebrae 26, total vertebrae 38.

Pectoral fin with one simple and eight branched rays. Pelvic fin i,5. First pelvic-fin ray shorter, second, third and fourth branched rays longer. Dorsal-fin i,6. Dorsal-fin unbranched ray slightly convex. First basal radial inserted in vertebra 7 and last basal radial anterior to neural spine of vertebra 12. Adipose fin long (22.6−26.7% of SL). Anal fin iv,8. Caudal skeleton composed of a plate formed by parhypural + hypurals 1 and 2 in lower lobe, upper lobe plate formed by hypurals 3 and 4 fused, hypural 5 free, and pleurostile fused to compound centrum. Caudal fin with i,8+9,i principal rays. Upper and lower caudal-fin lobes approximately symmetrical. Six to seven procurrents rays in dorsal and ventral lobes.

Color in alcohol. Background color of body yellowish dorsolaterally and white ventrolaterally. Irregular dark-brown patches formed by concentrated melanophores along lateral portion of body. Head yellowish. Five conspicuous dark brown saddles along dorsal portion of body: first just after head, second at dorsal-fin origin, third at insertion of last dorsal-fin rays; fourth at mid-point between dorsal and adipose fins. Anterior and posterior region at insertions of adipose fin densely darkly pigmented. Humeral region with a large dark blotch. All fins hyaline.

Distribution and habitat. The new species is only known from the rio Corrente, Upper Paraná River basin at the municipality of Aporé, in Goiás state, Brazil ( Fig. 1a ). Specimens were captured in fast-water habitat, associated with marginal vegetation ( Fig. 4 ).

Etymology. The specific epithet lepturus is from Greek lepto meaning slender, and oura meaning tail, in reference to the depressed caudal peduncle. An adjective.

Figures

FIGURE 1. Map of samples sites (a) and maximum likelihood three of COI data (b). Black bars represent the molecular criteria used to species delimitation. Black nodes indicate>90% bootstrap values from 1.000 pseudoreplicates; grey nodes indicate support between 70% and 90% bootstrap values. Colored symbols in the map and in the tree represent the species (Imparfinis lepturus—pink star; I. minutus—yellow diamond; Imparfinis mirini—blue circle; I. piperatus—light blue triangle; Imparfinis n.sp.—black hexagon and I. schubarti—red square). Topotype samples represented by asterisc. GR (Grande); IV (Ivinhema); PS (Paraíba do Sul); PN (Paranaíba); P (Paranapanema); RI (Ribeira do Iguape); SU (Sucuriú); T (Tietê); UT (Upper Tietê); V (Velhas).

FIGURE 3. Left column: Imparfinis lepturus, holotype, MZUSP 127602, 45.3 mm SL, from Rio Corrente, Upper Paraná basin, Aporé, Goiás. Right column: Imparfinis lepturus, paratypes, LBP 32018, from top to bottom: 51.8 mm SL; 44.2 mm SL; 33.3 mm SL.

FIGURE 4. Type locality of Imparfinis lepturus, Rio Corrente, Goiás state, Brazil. Photo: J. Crispim.

FIGURE 6. Live specimens of a) Imparfinis lepturus, LBP 32018; b) Imparfinis sp.n. LBP32067; c) Imparfinis mirini, LBP32005. Photo: J. Crispim.