Astyanax orthodus Eigenmann in Eigenmann & Ogle, 1907

Ruiz-C, Raquel I., Román-Valencia, César, Taphorn, Donald C., Buckup, Paulo A. & Ortega, Hernán, 2018, Revision of the Astyanax orthodus species-group (Teleostei: Characidae) with descriptions of three new species, European Journal of Taxonomy 402, pp. 1-45 : 19-22

Astyanax orthodus Eigenmann in Eigenmann & Ogle, 1907

Figs 3A , 4 , 8 , Table 2

Astyanax orthodus Eigenmann in Eigenmann & Ogle, 1907: 27 , fig. 23. Original description, type locality: Truando , Rio Atrato River Basin, Chocó, Colombia.

Diagnosis

Astyanax orthodus is a member of the orthodus species-group (as defined above) differing from A. villwocki, A. superbus , A. bopiensis nom. nov., A. gandhiae sp. nov. and A. yariguies by having a conspicuous, polygonal spot on the caudal peduncle that does not extend anteriorly to vertical line through posterior tip of anal fin (vs spot extending anteriorly as a stripe beyond vertical line through posterior tip of anal fin). It further differs from A. superbus by the absence of brown marks along the sides of body (vs presence of a series of longitudinal brown marks along the sides of body). It differs from A. boliviensis sp. nov. in having shorter, simple extension of the chevrons (vs chevron extension elongate and branched distally). It differs from A. gandhiae sp. nov. in having a reticulated pattern predominant over upper region of coelomic cavity (vs without reticulated pattern predominant over upper region of coelomic cavity). It differs from A. embera sp. nov. in the position, size and shape of the spot on the caudal peduncle, which does not extend to the dorsal and ventral margins of the caudal peduncle (vs caudal peduncle extending as a fan-shaped blotch that reaches, or almost reaches, the dorsal and ventral margins of the caudal peduncle, Fig. 3A ). The new species is distinct from A. moorii comb. nov. in having the distance between the dorsal and pectoral fins more than 40.4% HL (vs less than 40.3% HL), interorbital distance more than 32% HL (vs less 32% HL) and upper jaw length less than 31% HL (vs more than 45% HL).

Etymology

The specific epithet orthodus is latinized from Greek ‘ orthodon ’, meaning ‘straight tooth’, in reference to the straight posterior surface of the inner premaxillary teeth and the cusps, which Eigenmann (in Eigenmann & Ogle 1907) used to distinguish A. orthodus from A. bimaculatus .

Material examined

Holotype (examined from photograph)

COLOMBIA: 88.3 mm SL, NW Colombia, Department of Chocó, Rio Sucio Municipality, Urabá, Truandó River, lower Atrato River Basin, Caribbean coast ( USNM 55655 ).

Other material

COLOMBIA: Chocó: 2 ♀♀, 66.1–71.6 mm SL, Atrato River Basin, Truandó River, tributary Atrato River ( AMNH 5370 ) ; 2 ♀♀, 86.9 mm SL, Yuto, Atrato River Basin, Yuto River, tributary Atrato River (IAvHP 6494) ; 16 ♀♀, 32.3–100.7 mm SL, 2 ♂♂, 2 ♀♀, C&S, 51.4–67.8 mm SL, Rio Sucio municipality, vereda Sautatá, Atrato River Basin,Tendal Creek (IAvHP 7146) ; 11 ♀♀, 37.4–51.9 mm SL, Atrato River Basin, Rio Sucio Municipality, Sautata Strema (“vereda”), Tendal Creek (“quebrada”), Parque Natural Nacional Los Katios , 07°48′08″ N, 77°10′22″ W, 161 m a.s.l. (IAvHP 7208) ; 8 ♀♀, 32.6–76.1 mm SL, 2 ♀♀ C&S, 56.8–61.3 mm SL, rio Sucio Municipality, Sautata Stream (“vereda”), Atrato River Basin, Tendal Creek, Parque Natural Nacional Los Katios ( IAvHP 7209 ) ; 2 ♀♀, 82,6– 99.4 mm SL, Sucio River, Sautata Stream (“vereda”), Atrato River Basin,Tendal Creek, Parque Natural Nacional Los Katios (IAvHP 7210) ; 1 ♂, 71.5 mm SL, Acandí, Atrato River Basin, tributary of Nati River ( IUQ 1319 ).

Description

Body compressed, greatest body depth at or anterior to dorsal-fin origin. Mouth terminal. Dorsal anterior profile of head sigmoid, concave between snout tip and posterior margin of supraoccipital crest, convex between supraoccipital and dorsal fin, convex between last dorsal-fin ray and adipose-fin origin. Dorsal and ventral caudal peduncle margins straight. Ventral profile convex from tip of snout to pelvic-fin insertion.

Premaxillary teeth in two series; outer series with four tricuspid teeth covering three internal teeth of inner series; inner row with five pentacuspid teeth. Maxilla long, of same width along entire length, with 2–3 tricuspid teeth set in anterior most part of ventral margin. Dentary with anterior four teeth pentacuspid, followed laterally by 8–10 smaller teeth of increasing posterior inclination and reducing from tri to unicuspid, total number of lateral teeth quite variable.

Pored lateral-line scales 35(1), 37(6), 38(10), 39(4), 40(6), 41(1), 42(1) (n = 29), scales between lateral line and origin of dorsal fin 7(27), 8(3) (n = 30), scales between lateral line and origin of anal fin 8 (4), 9(24) (n = 28), scales between lateral line and pelvic-fin insertion 6(27), 7(3) (n = 30). Dorsal-fin rays iii 9 (30), predorsal midline covered with medial, bilobed scales for more that ¾ of its length, naked anteriorly. Postdorsal profile convex, from last dorsal-fin ray to adipose-fin origin; first simple ray small, only visible in cleared and stained specimens; second simple ray about half length of third simple ray. Distal margin of dorsal fin slightly convex. Adipose-fin origin anterior to vertical through insertion of last anal-fin ray. Pectoral-fin rays i 11 ii (15), i 12 (7) (n = 22). Anal-fin rays iv–v 24 (1), 26(1), 27(6), 28(8), 29(5), 30(3), 31(1) (n = 27). Anal-fin origin posterior to vertical through insertion of last dorsalfin ray ( Table 1 ). Caudal fin with 10 (6) leading principal rays in dorsal and ventral lobes, each lobes with 8(6) procurrent rays.

Total vertebrae 34(4), 35(2), including those of Weberian apparatus: 16(4)–17(2) precaudal centra, last three without ribs; caudal centra 18(4)–19(2). Epipleurals 20(4)–21(2). Epineurals 30(4), 31(2); posterior most epineural may reach anterior surface of urostyle. Hypurals 7(6), first dorsal hypural with anterior margin swollen, without projections that articulate with the urostyle; second and third hypurals with anterior margin swollen and contacting urostyle.

Pigmentation in alcohol

Sides of body yellowish, with reticulated pattern predominant over upper region of coelomic cavity, silvery stripe present from humeral region to caudal-peduncle base, overlain by series of chevronshaped marks formed by dark lines along myosepta between myotomes extending from dorsal region of coelomic cavity to caudal peduncle; pigmented muscle septae forming chevrons not coinciding with scale rows. Chevrons present in juveniles, immature specimens and adults, without distal extensions. Dorsal region of head and body chestnut brown. Sides of head and ventral surface of body light brown, not silvery. Melanophores of humeral region forming two spots. Anterior spot formed by two layers of pigment: brown melanophores distributed in a thin superficial layer of the epithelium (Layer 1, Fig. 1 ), deeper layer of dark melanophores (Layer 2, Fig. 1 ). Layer 2 forming a polygon-shaped spot, consisting of two groups of melanophores that do not precisely overlap, forming four-sided spot, extending from third to sixth or seventh scale of lateral line. Posterior humeral spot situated two or three scales posterior to the anterior humeral spot, arc- or sigmoid-shaped, inconspicuous, covering two to three scales above lateral line. Scales on sides of body with spots or dots. Spot on caudal peduncle pentagonal, located over lateral axis of peduncle, prolonged on posterior tips of middle caudal-fin rays, not extending to dorsal and ventral margins of caudal peduncle. Pectoral fins mostly hyaline, melanophores present on distal tips of pelvic-fin rays and interradial membranes of dorsal, caudal and anal fins.

Sexual dimorphism

Sexually dimorphic characters observed in one male, consisting of 7 to 12 small hooks located on distal portions of all branched anal-fin rays.

Distribution

Astyanax orthodus has been reported from the Pacific slopes of Central America ( Angulo et al. 2013) and Colombia in South America ( Torres-Mejía et al. 2012). However, based on the results of this study, A. orthodus occurs only in the lower Atrato River Basin, which flows into the Caribbean Sea in the Truando Department of north-western Colombia ( Fig. 4 ). Populations identified as A. orthodus outside of the Atrato River Basin and similar to A. embera sp. nov., described herein, represent an as yet unrecognized new species.

Figures

Fig. 3. Shape of caudal-peduncle spot in species of the Astyanax orthodus species-group. A. Astyanax orthodus Eigenmann, 1907. B. Astyanax embera sp. nov. Scale bar = 1 cm.

Fig. 4.Distribution of speciesof the Astyanaxorthodus species-group(symbol includestypelocalities).

Fig. 8. Astyanax orthodus Eigenmann, 1907. A. Holotype, 88.3 mm SL, Truando River, Atrato River Basin, Chocó, Pacific coast of Colombia (USNM 55655). B. 32.5 mm SL,Vereda Sautatá,Atrato River drainage, Chocó, Pacific coast of Colombia (IAVH 7146). Scale bars = 1 cm.

Fig.1.A.DistributionofpigmentinthehumeralregionofAstyanaxspecies.B.A.bimaculatus(Linnaeus, 1758).C.A.caucanus(Steindachner,1879).D.A.mexicanus(DeFilippi,1853).E.A.courensisBertaco, Carvalho & Jerep, 2010 (modified from Bertaco et al. 2010). The anterior humeral spot consists of two overlapping layers of pigment identified by numbers 1 and 2 (see Román-Valencia et al. 2015: fig. 1): 1. Diffuse vertical bar. 2. Horizontal spot with concentrated pigments.