Cyphocharax orion, Melo & Faria, 2024

Melo, Bruno F. & Faria, Tiago C., 2024, Description of a new species of Cyphocharax from the rio Juma, rio Aripuanã basin, southern Amazon basin (Teleostei: Curimatidae), Neotropical Ichthyology (e 230122) 22 (1), pp. 1-12 : 3-7

Cyphocharax orion , new species urn:lsid:zoobank.org:act:015D806B-E348-44DB-B4BB-96048949813F

( Figs. 1–2 ; Tab. 1)

Holotype. LBP 34856, 72.8 mm SL, Brazil, Amazonas , Apuí , rio Juma , rio Aripuanã , Madeira system, Amazon basin, 07°16’43.31”S 60°03’23.96”W, 8 Dec 2022, T. C. Faria, I. L. P. Monteiro & M. A. Pinheiro.

Paratypes. All from rio Juma , rio Aripuanã , rio Madeira, Amazon basin, collected with holotype. LBP 33070 , 4 (tissues #112660–112663), 56.2–61.8 mm SL. ZUEC 18036 , 1 , 77.8 mm SL .

Diagnosis. Cyphocharax orion distinguishes from all congeners, except C. laticlavius Vari & Blackladge, 1996 , C. modestus (Fernández-Yépez, 1948) , C. naegelii (Steindachner, 1881) , C. pantostictos Vari & Barriga Salazar, 1990 , and C. sanctigabrielis , by having a horizontally elongated caudal-peduncle blotch of dark pigmentation running from the vertical line through the adipose-fin terminus to the base of median caudal-fin rays (vs. absence or blotch relatively small and confined to caudal-peduncle region). Cyphocharax orion differs from C. laticlavius by the absence of a midlateral dark stripe extending from midbase of dorsal fin to basal portions of middle caudal-fin rays (vs. presence), and head length 24.5–26.2% of SL (vs. 29.6–34.3% of SL). Cyphocharax orion differs from C. modestus by having 4.5 scales from dorsal-fin origin to lateral line (vs. 5.5–7) and head length 24.5–26.2% of SL (vs. 27–31% of SL). Cyphocharax orion differs from C. naegelii by having 29 scales in lateral line (vs. 39–45). The new species differs from C. pantostictos by the absence of dark spots over the center of scales on the lateral and dorsolateral region of the body (vs. presence) and distance from snout tip to anal-fin origin 77.5– 81.3% of SL (vs. 83–85% of SL). Finally, C. orion differs from C. sanctigabrielis by having relatively thin and uniform caudal-peduncle blotch (vs. caudal-peduncle blotch thick and posteriorly wider), number of lateral-line scales 29 (vs. 31), distance between dorsal-fin origin and pelvic-fin origin 33.5–37.9% of SL (vs. 30.9–33.0% of SL), distance between dorsal- and pectoral-fin origin 34.6–37.1% of SL (vs. 32.2–34.0% of SL), and postorbital length 39.8–43.2% of SL (vs. 33.1–39.0% of SL).

Description. Morphometric data in Tab. 1. Dorsal profile of head convex from tip of snout to head at line through anterior margin of orbit; nearly straight from that point to tip of supraoccipital; slightly concave from that point to dorsal-fin origin; nearly straight to adipose-fin origin; gently concave to origin of anterior dorsal caudal-fin procurrent ray. Ventral profile convex from chin to terminus of anal-fin base; gently concave to origin of anterior ventral procurrent ray of caudal fin. Prepelvic region somewhat flattened transversely. Postpelvic region of body transversely rounded.

Head profile rounded anteriorly. Lower jaw of same size than upper jaw. Mouth subterminal, horizontally aligned with ventral margin of orbit. Nostrils separated; anterior nostril circular to ovoid, posterior nostril elongated dorsoventrally. Three thin flaps on buccopharyngeal complex. Adipose eyelid slightly developed anterior to orbit.

Dorsal fin pointed, with distal margin straight and first and second branched rays longest. Margin of pectoral fin pointed. Tip of adpressed pectoral fin reaching three or four scales short of vertical through pelvic-fin origin. Pelvic fin profile slightly rounded. Tip of adpressed pelvic fin reaching four scales short of anal-fin origin. Caudal fin forked. Adipose fin present. Anal fin emarginate, anterior branched rays one-third length of ultimate ray. Tip of adpressed anal fin reaching three scales short of origin of ventral caudal-fin ray.

Lateral line longitudinal scales from supracleithrum to hypural joint 29*(6). Continuous series of scales posterior to hypural joint 3*(6). Scales in transverse series from dorsal-fin origin to lateral line 4.5*(6). Scales in transverse series from lateral line to anal-fin origin 4*(1) or 5(5). Series of scales between anus and anal-fin origin 1(2) or 2*(4). Predorsal scales 8*(4) or 9(2). Circumpeduncular scales 16*(6).

Dorsal-fin rays iii,9*(6), first unbranched ray very short. Anal-fin rays iii,6(1) or iii,7*(5), first ray very short. Pelvic-fin rays i,8*(6). Pectoral-fin rays i,12*(3) or i,13(3). First gill arch with 8*(1) or 9(5) rakers on upper limb and 13*(1), 14(2) or 15(3) rakers on lower limb.

Coloration in alcohol. Ground coloration of formalin-fixed specimens olivaceous to silvery ( Fig. 2 ). Dusky surface coloration, darker on dorsal portion of head; head dusky dorsolaterally and light colored ventrally. Dark chromatophores on opercle slightly larger than those on snout. Dusky surface coloration darker on dorsal and dorsolateral regions of body, with dark chromatophores dense on scales above lateral line, less concentrated on lateral line and almost absent on scales below lateral line. Reticulate pattern on almost all body due to higher concentration of dark chromatophores on scale margins, with anterior margin sometimes separated from middle region of scales by dark line of chromatophores. Reticulate pattern more conspicuous on middle region of body due to contrasting regions of scales; pattern not evident in ventral region of body, disappearing around fourth or fifth scale row below lateral line. Deep-lying, dark chromatophores forming faint, dusky midlateral stripe on body. Stripe more evident posterior of vertical through adipose-fin terminus, forming a longitudinally elongated caudal peduncle blotch that extends into base of middle caudal-fin rays. Middorsal region of body darker with dark stripe extending from tip of supraoccipital to dorsal margin of procurrent caudal-fin rays. Dorsal, anal, and caudal fins somewhat dusky with margins outlined by small, dark chromatophores. Dark pigmentation developed proximally on caudal-fin lobes, dorsal and anal fins. Pectoral and pelvic fins with rays outlined by small, dark chromatophores. Adipose fin speckled with small dark chromatophores.

Geographical distribution. Cyphocharax orion is known from the rio Juma, which is a tributary of the rio Aripuanã, itself a right-bank tributary of the rio Madeira basin, Amazon basin ( Fig. 3 ). Specimens were collected along the BR-230 Transamazônica between Apuí and Santo Antônio do Matupi, Amazonas, Brazil. The distribution suggests that C. orion is restricted to the Aripuanã basin.

Ecological notes. Cyphocharax orion was collected in a blackwater pond of rio Juma, characterized by a sand, dead leaf, and debris-filled bottom, and partially shadowed by the BR-230 Transamazônica road bridge ( Fig. 4 ).

Etymology. The epithet orion derives from Ancient Greek ὨΡΊων (Ōríōn) which means “heaven’s light”, or Arion, which means “warrior”. In ancient Greek mythology, Orion was a giant hunter who, after being killed by Scorpion sent by Earth mother Gaia, either Zeus or Artemis placed in the night sky as the constellation Orion. The Orion Constellation contains the Great Orion Nebula, one of the brightest nebulae in the visible sky, and the Orion’s Belt asterism formed by three bright blue supergiants: the triple star system Alnitak, the major star Alnilam, and the multiple star system Mintaka. The name Cyphocharax orion is in allusion to three major southern Amazonian rivers Madeira, Aripuanã (type-locality), and Tapajós, and symbolizes the resistance to anthropogenic pressures with strength, bravery, and universe brilliance. A noun in apposition.

Conservation status. The region has been impacted with diffuse human activities,

like the construction of the BR-230 Transamazônica road that longitudinally spans the Amazon rainforest and Caatinga from Lábrea-Amazonas to Cabedelo-Paraíba in northeastern Brazil. However, at least three enormous, protected areas exist near the type-locality: the Floresta Nacional do Aripuanã, the Floresta Nacional do Jatuarana,

and the Parque Nacional do Acari. The small sample size is likely due to the lack of fieldwork efforts in the region. Given the current information, we suggest the category Least Concern (LC) for Cyphocharax orion under the categories and criteria of the International Union for Conservation Nature (IUCN Standards and Petitions

Subcommittee, 2022).

Figures

FIGURE 1 | Cyphocharax orion, LBP 34856, holotype, 72.8 mm SL, rio Juma, rio Aripuanã basin, Apuí, Amazonas, Brazil.

FIGURE 2 | Cyphocharax orion: A. ZUEC 18036, paratype, 77.8 mm SL, formalin-fixed specimen; B. LBP 33070, 57.9 mm SL, ethanol-fixed specimen; rio Juma, rio Aripuanã, Apuí, Amazonas, Brazil.

FIGURE 3 | Map of southern Amazon basin indicating the type-locality of Cyphocharax orion (black circle) in the rio Juma near the town of Apuí, Amazonas, Brazil.

FIGURE 4 | Rio Juma, affluent of rio Aripuanã, Apuí, Amazonas, Brazil. Photography: Tiago C. Faria.