Schizodon paucisquamis, Britski & Garavello & Ramirez, 2023

Britski, Heraldo A., Garavello, Júlio C. & Ramirez, Jorge L., 2023, Description of a new species of Schizodon (Characiformes: Anostomidae) from the upper rio Tapajós basin, Brazil, Zootaxa 5330 (1), pp. 135-140 : 136-139

Schizodon paucisquamis , n. sp.

( Figs 1–2 )

Schizodon trivittatus (not Garavello, Ramirez, Oliveira, Britski, Birindelli & Galetti, 2021): Garavello et al., 2021: 19 (in part; lot MZUSP 103676).

Holotype: MZUSP 127765 (329.0 mm SL), Brazil, Mato Grosso, Porto dos Gaúchos, rio Arinos , c. 11°32’S, 57°25’W; M. Goulding, M.L. Carvalho & L.P.S. Portugal, 18 Aug 1984 . Paratypes: All from Brazil, Mato Grosso. MZUSP 103676 (4, 150.9–300.0 mm SL), rio Arinos , Ilha do Túlio , about 3 km upstream from its mouth on the Rio Juruena , c. 10°27’S, 58°17’ W; F.A. Machado, C. H. Melo, C. M. Leite & M. F. Catarino, 24–25 July 1997. MZUSP 83553 (9, 172.2–350.0 mm SL), same data as holotype.

Diagnosis. Schizodon paucisquamis is distinguished from all other species of Schizodon by having 12 (versus 16–20) circumpeduncular scales. Large specimens (larger than 250 mm SL) can be further distinguished by the presence of a large black blotch at the end of the caudal peduncle, its diameter equal to or greater than the diameter of the eye (versus caudal peduncle blotch, when present approximately rounded, its diameter much smaller than eye diameter).

Description. Morphometric data of holotype and paratypes in Table 1 . Large sized species when compared with congeners, largest examined specimen 350 mm SL. Head and body elongate and moderately compressed ( Figs. 1–2 ). Dorsal profile strongly convex from snout tip to vertical through anterior border of nostril, straight from latter point to supraoccipital spine, slightly convex from that point to dorsal-fin origin, straight along dorsal-fin base, slightly convex from dorsal-fin terminus to adipose fin, and distinctly concave from adipose fin to the anteriormost dorsal caudal-fin procurrent ray. Ventral profile convex from tip of lower jaw to pelvic-fin origin; straight or slightly convex from pelvic-fin base to anus, straight from anus to anal-fin origin, straight along anal-fin base, and distinctly concave from anal-fin terminus to anteriormost ventral caudal-fin procurrent ray. Greatest body depth at origin of dorsal fin. Head slightly depressed; mouth terminal; upper and lower jaws meet along horizontal bisecting middle of eye or slightly below. Upper lip smooth, lower lip with barely apparent ridges oriented antero-posteriorly. Premaxilla and dentary with four asymmetrical, tetracuspid teeth. Teeth on each jaw graduated in size, with symphyseal teeth largest. Posterior tooth much smaller than preceding three teeth. Posterior (fourth) cusp smallest on each tooth, with third cusp largest. Difference in size between third and fourth cusps most pronounced on second tooth of dentary.

Fins not scaled except for basal portion of caudal fin. Scales extend to posterior margin of hypural plate and on basal portion of middle caudal fin rays. Scales cycloid. Lateral line with 40*(1), 41(6) or 42(7) perforated scales extending from posterior margin of opercula to base of median caudal-fin rays. Horizontal scale rows between dorsal-fin origin and lateral line 4*(14). Horizontal scale rows between lateral line and pelvic-fin origin 4*(11) or 4.5(3). Horizontal scale rows around caudal peduncle 12*(14). Predorsal scales from tip of supraoccipital to dorsal-fin origin 11(14). Dorsal scales from dorsal-fin end to adipose-fin origin 13(1), 14*(3), 15(4), 16 (3), or 17(1). Dorsal scales between adipose-fin end and first dorsal procurrent caudal-fin rays 6*(1), 7(3), 8 (6) or 9(4). Prepelvic scales 14(1), 15(2), 16(8), or 17*(3). Scales from pelvic-fin base to anus 13(5), 14*(6), 15(1), or 16 (1). Scales between anus and anal-fin origin 1(13) or 2(1). Scales from anal-fin end and first procurrent caudal-fin ray 6*(4), 7(5), 8(4) or 9 (1). Base of anal-fin rays covered by a single row of five to seven small elongate scales. Dorsal-fin rays ii,9, ii* (13) or ii,10, ii (1). Dorsal-fin origin at vertical through first or second scale in front of pelvic-fin origin. Dorsal-fin distal margin gently convex. Adipose fin small, its base at vertical through middle of anal-fin base. Pectoral-fin rays i,14(4), i,15(6), i,16*(3) or i,17(1). Tip of pectoral-fin rays extending to third or fourth scale in front of pelvic-fin origin. Pelvic-fin anterior base at vertical through base of first to third branched dorsal-fin ray. Pelvic-fin rays i,8*(13) or i,9(1). Tip of pelvic fin reaching between seventh to ninth scales in front of anus. Anal-fin rays ii, 7, ii*(14). Anal-fin origin at vertical through second or third scale in front of adipose fin. Distal margin of anal fin concave extending to last or penultimate scale of ventral row. Anterior most branched anal-fin ray about twice longer than posterior most ray. Last anal-fin ray usually split to its base. Principal caudal-fin rays i, 8,9, i*(14). Caudal fin forked, with lobes approximately similar in size or upper lobe slightly longer than lower lobe. Vertebrae 37(2), vertebrae 5 to 24 bearing ribs, 4(2) branchiostegal rays.

Color in alcohol. Body with five dark brown or dark gray blotches, typically vertically elongated from the dorsum to the second row of scales below the lateral line, variable in size and intensity, typically darker at the level of the lateral line. First blotch located halfway between vertical through supraoccipital tip and dorsal-fin origin; second blotch at level of dorsal fin, wider and in some individuals divided into two similar blotches; third blotch located halfway between end of dorsal-fin base and origin of the anal-fin base; fourth blotch slightly ahead of adipose fin, in small individuals (up to 200 mm SL) quadrangular-shaped, longitudinally elongated; fifth blotch at the caudal peduncle black, intensely-pigmented and large, slightly square shaped in specimens up to 250 mm SL or rounded, greater than eye diameter, in larger specimens. Smaller individuals (up to 200 mm SL) also show vestiges of a longitudinal stripe along the lateral line. Scales with dark brown chromatophores; those of the antero-dorsal region of the body with small lighter areas on its central region, wider in ventralmost and posteriormost scales. Scales on the ventral area typically very clear or presenting pearly margins, contrasting with their basal area. Chromatophores of each scale forming dark longitudinal lines, sometimes inconspicuous, between the rows of scales. Fins hyaline; melanophores scattered on membranes between fin rays. Pelvic and anal fins lighter than remaining fins. Dorsal and caudal fins darker than pectoral fin. Adipose fin with dark distal margin.

Distribution. Schizodon paucisquamis is only known from the rio Arinos, a tributary of the rio Juruena, rio Tapajós basin, Mato Grosso state, Brazil ( Fig. 3 ).

Etymology. The species epithet is an adjectivized noun combining the Latin paucus, few, and squama, referring to the reduced circumpeduncular squamation of caudal peduncle that is a distinguishing feature of the species.

Remarks. The color pattern of the new species is basically the same as that of Schizodon fasciatus and S. trivittatus , which, as several other species of the genus, present four transversal blotches located in a similar position of the body. However, in large specimens (over 300 mm SL), the caudal peduncle blotch of the new species has a unique feature among congeners, due to its circular shape, slightly larger size than the eye, and intense black pigmentation. This unique feature, however, can only be used to distinguish relatively large-sized (larger than 250 mm SL) individuals. Smaller-sized paratypes (smaller than 250 mm SL) have the caudal peduncle blotch proportionally smaller, although still relatively large and quadrangular-shaped.

Schizodon paucisquamis is only known from the rio Arinos, at its lower to middle stretches. The rio Arinos is a tributary of the rio Juruena, which joins the rio Teles Pires forming the rio Tapajós, one of the larger tributaries of the Amazon basin. Both the rio Arinos below Porto dos Gaúchos and the rio Juruena have rapids in their courses, which may have represented, over time, barriers to the free dispersion of some fish species. Thus, S. paucisquamis may represent an endemic species to the rio Arinos basin, or at least from the rio Juruena basin. The hypothesis of endemism of the species to this portion of the rio Tapajós basin is reinforced by the fact that many fish inventories have been carried out in this river basin in recent decades, and no specimens of this large species have been collected, except in the rio Arinos.

Comparative material examined. All from Brazil except if otherwise noted. Schizodon altoparanae: MZUSP 41102, holotype, 282.0 mm SL, Mato Grosso do Sul, rio Paraná at Jupiá ; MZUSP 41103 to 41120 , paratypes, 28, 138.3–232.1 same locality as holotype. Schizodon borellii: MZUSP 2908 , 1, 255.0 mm SL, Mato Grosso do Sul, Coxim, Rio Piquiri ; MZUSP 62715 , 1, 223.0 mm SL, Mato Grosso, Cuiabá, mouth of Varadouro ; MZUSP 41146 , 2, 290.0–298.0 mm SL, Mato Grosso, Cuiabá, Rio Coxipó da Ponte , São Gonçalo . Schizodon corti: USNM 121300, 1, 257.0 mm SL, holotype of S. fasciatus corti , Venezuela, rio Palmar, near Totuma , Lake Maracaibo basin. Schizodon dissimilis: MCZ 19383, lectotype, 264.6 mm SL, Piauí, rio Puty (= Poti), tributary of rio Parnaíba ; MZUSP 55143 , 4, 196.0–220.0 mm SL, rio Jaguaribe ; MZUSP 55144 , 1, 155.0 mm SL, Lima Campos, rio Jaguaribe , ribeirão São João . Schizodon fasciatus: MZUSP 20972, 15, 170.0–295.0 mm SL, Amazonas, Fonte Boa, Paraná of Iupiá ; MZUSP 7518 , 5, 110.0–130.0 mm SL, Amazonas, Paraná de Urucará, Urucará ; MZUSP 62720 , 5, 115.0–240.0 mm SL, Amazonas, Lago Castro, mouth of rio Purus . Schizodon isognathus: MZUSP 4397, 1, 307.0 mm SL, Brazil, Mato Grosso, rio Cuiabá, Santo Antonio do Leverger ; MZUSP 36719 , 1, 176.0 mm SL, Itiquira, Rio Piquiri , Porto Chinelo . Schizodon jacuiensis: MZUSP 38864, paratype, 111.0 mm SL, Rio Grande do Sul, Porto Alegre, rio Guaíba , Morro do Sabiá . Schizodon knerii: MZUSP 94051, 4, 75.1–86.8 mm SL, Bahia, rio Formoso , tributary of the rio Corrente ; MZUSP 95159 , 2, 155.0–167.0 mm SL, Minas Gerais, Três Marias dam, rio São Francisco . Schizodon nasutus: MZUSP 2023 , 5, 87.0– 100.8 mm SL, São Paulo, rio Piracicaba , Piracicaba; MZUSP 42844 , 17, 96.0–206.0 mm SL), São Paulo, rio Paraná , Ilha Solteira . Schizodon platae: MCZ 833, holotype, not measured, Argentina, Rosario, La Plata ; MZUSP 47691 , 1, 102.0 mm SL, Argentina, rio de La Plata , Buenos Aires. Schizodon rostratus: MCZ 19380, holotype, 180.0 mm SL, Piauí, rio Poti , tributary of Rio Parnaíba , Terezina; MCZ 69542 , 4, 172.0–185.0 mm SL, Piauí, rio Poti , tributary of rio Parnaíba at Terezina. Schizodon scotorhabdotus: MZUSP 27969, paratypes, 3, 83.0–148.0 mm SL, Venezuela, caño to W of road from Calabozo to San Fernando, about 35 km to S of Masaquara farm ( Caño Falcon ). Schizodon trivittatus: MZUSP 115362, holotype, 285.0 mm SL, Mato Grosso, São José do Couto, rio Culuene ; MZUSP 36835 , 3, 149.0–252.0 mm SL, Pará, Altamira, rio Xingu , Cachoeira do Espelho . Schizodon vittatus: MZUSP 21334, 3, 173.0–192.0 mm SL, Pará, Tucuruí, rio Tocantins . LISDEBE 7343 , 6, 226.0–280.0 mm SL, Goiás, rio Araguaia .

Figures

FIGURE 1. Schizodon paucisquamis MZUSP 127765, holotype, 329 mm SL.

FIGURE 2. Schizodon paucisquamis, MZUSP 103676, paratype, 150.0 mm SL, radiograph in lateral view.

FIGURE 3. Map of northern portion of Brazil showing the distribution of Schizodon paucisquamis (yellow dot; yellow star: type locality), S. trivittatus (orange dots), S. vittatus (blue dots) and S. fasciatus (red dots). Rivers indicated as follows: 1. Amazonas, 2. Tapajós, 3. Xingu, 4. Araguaia, 5. Tocantins. Some symbols may represent more than one sampling locality.