Myloplus zorroi, Andrade, Marcelo C., Jegu, Michel & Giarrizzo, Tommaso, 2016

Andrade, Marcelo C., Jegu, Michel & Giarrizzo, Tommaso, 2016, A new large species of Myloplus (Characiformes, Serrasalmidae) from the Rio Madeira basin, Brazil, ZooKeys 571, pp. 153-167 : 154-161

Taxon classification Animalia Characiformes Serrasalmidae

Myloplus zorroi sp. n. Figures 1a, b; 2and 4a, b, c; Table 1

Tometes sp.: Camargo and Giarrizzo 2007: 294 [Checklist of fish species of the Marmelos Conservation Area (BX044)].

Holotype.

INPA 50880 (326.2 mm SL), Amazonas, Apuí, Corredeira dos Periquitos, Rio Aripuanã, 07°17'19.8"S, 60°38'10.0"W, 19 November 2014, Machado V. N. et al.

Paratypes. All from Brazil. INPA 50868 (3 specimens 183.8-339.5 mm SL), collected with holotype. MPEG 30680 (1 specimen 351.1 mm SL), Mato Grosso, Aripuanã, downstream of Salto de Dardanelos, Rio Aripuanã, 10°09'46.5"S, 59°26'54.9"W, 12 December 2014, V. Machado. MPEG 30663 (1 specimen 244.5 mm SL), INPA 48546 (1 specimen 249.9 mm SL), and ZUEC 10776, (1 specimen 246.5 mm SL), Brazil, Amazonas, Novo Aripuanã, Parque Nacional dos Campos Amazônicos, Rio Roosevelt, Madeira Basin, 8°11'51"S, 60°58'19.2"W, October 2003, M. Camargo–Zorro & T. Giarrizzo.

Diagnosis.

Myloplus zorroi sp. n. can be distinguished from its congeners by the absence of abdominal keel and the prepelvic serrae formed by 13-19 low spines (Fig. 2), in contrast to a well-marked abdominal keel and prepelvic serrae of more than 20 high spines. The new species is distinguished from Myloplus asterias , Myloplus levis , and Myloplus torquatus by the presences of fewer branched dorsal-fin rays (20-22 versus 23 or greater), and from Myloplus arnoldi , Myloplus ternetzi , and Myloplus torquatus by having a greater number of branched anal-fin rays (32-34 versus 31 or fewer). Myloplus zorroi differs significantly from Myloplus lobatus , Myloplus schomburgkii , and Myloplus rhomboidalis by having two rows of premaxillary teeth forming a slight arc (e.g., Fig. 3a) versus two rows of premaxillary teeth forming a shape that resembles the uppercase letter “A” (Fig. 3b). The shorter dorsal-fin base (27.6-30.1% of SL versus 31.8% of SL or higher), and the larger interdorsal distance (11.4-12.7% of SL versus 10.8% of SL or lower) are useful to distinguish Myloplus zorroi from Myloplus asterias , Myloplus levis , Myloplus ternetzi , and Myloplus torquatus . Furthermore, the new species differs from Myloplus ternetzi by the presence of a pair of symphyseal teeth versus their absence. The smaller vertical diameter of the eye (27.3-35.4% of HL versus 35.5% of HL or greater) separates Myloplus zorroi from Myloplus arnoldi , Myloplus asterias , Myloplus levis , Myloplus lobatus , and Myloplus ternetzi . Myloplus zorroi is additionally distinguished from Myloplus arnoldi and Myloplus torquatus by having a greater number of total vertebrae (40-41 versus 37 or less), by having anterior dorsal-fin rays lacking pigmentation (versus strongly dark pigmented anterior dorsal-fin rays in Myloplus arnoldi ), and the presence of a diffuse dark band at caudal-fin distal border (versus the presence of a well-defined dark band in Myloplus arnoldi ). The elongated fontanel with similarly sized anterior and posterior portions (versus very short posterior fontanel and rounded anterior fontanel) further distinguishes Myloplus zorroi from Myloplus asterias .

Description.

Morphometric data is presented in Table 1. Body laterally compressed, ovoid profile, greatest body depth at dorsal-fin origin (Fig. 1a, b). Dorsal profile of head distinctly convex from upper lip to vertical through anterior nares, nearly concave or gently straight from that point to distal margin of supraoccipital spine, and distinctly convex from that point to dorsal-fin origin. Dorsal-fin base slightly convex. Profile straight from dorsal-fin terminus to adipose-fin origin. Ventral profile of head slightly concave; ventral profile of body distinctly convex. Caudal peduncle relatively short, profile of lower caudal peduncle slightly concave. Anal-fin base distinctly convex at its basal third.

Snout gently rounded, mouth terminal, slightly oriented dorsally; jaws equal in size. Labial row of premaxillary teeth separated from lingual row by a gap; five teeth in labial row and two teeth in lingual row (Fig. 4a). Premaxillary and dentary teeth molariform. Premaxillary teeth 1-3 of labial row with sharp edges, concave in lateral view, contralateral labial series separated by distinct gap, molariform teeth 1-2 with oval base, broad anteroposteriorly, molariform tooth 3 base rounded (Fig. 4a); 4 and 5 with elongate base anteroposteriorly, distinctly concave in lateral view, and cutting edge slightly curved internally. Premaxillary teeth 1'-2' of lingual row with base somewhat trapezoidal, with cutting edge curved, and concave labial face. Dentary with 5 (2) or 6* (6) teeth, first tricuspid, 2-5 bicuspid, anterior cusp largest. Symphyseal tooth posterior to main series present. Symphyseal teeth with blade-shaped anterior margin (Fig. 4b). Maxillary edentulous. First branchial arch with gill rakers elongated, stiff, and recurved. Epibranchial gill rakers 10 (1), 11 (1), or 13 (1). Ceratobranchial gill rakers 14 (1), 15 (1), or 18 (1); one gill raker at cartilage between ceratobranchial and epibranchial.

Scales cycloid, lateral line with 80 (1), 81 (3), 82 (2), or 83* (2) perforated imbricate scales from supracleithrum to hypural joint; total perforated scales 85 (1), 86 (2), 87 (1), 88* (2), or 89 (2). Scale rows between dorsal-fin origin and lateral line 39 (1), 40* (3), 41 (2), or 42 (2). Scale rows between lateral line and pelvic-fin insertion 36 (2), 38* (2), 39 (2), 40 (1), or 42 (1). Circumpeduncular scales 34 (1), 35* (3), or 36 (4). Prepelvic serrae with 13 (1), 17 (2), 18 (2), or 19* (3) very reduced spines (Fig. 2), 8 (2), 9* (4), or 10 (2) simple postpelvic spines, and 5 (1), 6* (6), or 7 (1) double postpelvic spines. Total spines 28 (1), 31 (2), 33 (1), 34* (3), or 35 (1).

Pectoral-fin rays i, 16 (2), i, 17 (5), or i, 18* (1). Pelvic-fin rays i, 7* (7), or i, 8 (1). Dorsal-fin origin at midbody preceded by strong forward-directed spine. Dorsal-fin rays ii* (4), or iii (4), and 20 (3), 21* (4), or 22 (1); anteriormost rays longest. Anal-fin rays iii (7), or iv* (1), and 32 (3), 33* (2), or 34 (3). Adipose fin with sub-rectangular distal margin. Caudal fin forked into lobes of similar size.

Total vertebrae 40 (1), or 41 (2). Predorsal vertebrae 10 (3). Postdorsal vertebrae 15 (2), or 16 (1). Vertebrae through last dorsal-fin pterygiophore and first anal-fin pterygiophore 2 (1), or 3 (2). Supraneurals 6 (3). Neurocranium in lateral view high, short, triangular, with concavity at epiphyseal bar level. Ascending process of premaxilla broader from its base to tip, with slightly rounded edge (Fig. 4c). Lateral process of premaxilla after the last labial premaxillary tooth well developed, its length almost or more than three times the base length of the most posterior labial premaxillary tooth. Mesethmoid in dorsal view short, triangular, with broad base. Cranial fontanel elongated, with epiphyseal bar dividing anterior cranial fontanel and posterior cranial fontanel in equal parts. Dorsal process of supraoccipital spine very high.

Color in alcohol. Ground coloration silver brownish to yellowish silver, with pale hues. Darker coloration on humeral region. Overall pigmentation of head above eye somewhat darker than that of adjoining areas. Body more yellowish postero-ventrally on anal-fin region. Darker blotches, irregular in size and shape, scattered on the flanks (Fig. 1a, b) mainly in males. Dorsal, anal, and caudal fins somewhat yellowish, with distal margins darker, most conspicuous on the caudal fin. Pectoral and adipose fins overall hyaline. Pelvic fin hyaline with distal margin darker. Edge of teeth brownish (Fig. 4 a–c).

Color in life. Based on photos of specimens collected by sport fishermen at Rio Aripuanã, Myloplus zorroi sp. n,. has ground coloration reddish silver, inconspicuous darker marks distributed on flanks, dorsum and head more darkened, and belly pale yellow. Dorsal, adipose, anal, and caudal fins yellowish brown.

Sexual dimorphism. The main secondary feature in mature males of Myloplus zorroi sp. n. is the additional anal-fin lobe centered on the 14th branched ray (Fig. 1b). Darker and irregularly shaped blotches are present over flanks at maturity (Fig. 1a, b). Filamentous extensions on dorsal fin and stiff hooks laterally curved on anal fin found in species of Tometes , Myleus , Mylesinus , and other Myloplus species were not present in three examined males of Myloplus zorroi sp. n.

Distribution.

Myloplus zorroi is known from Aripuanã and Roosevelt rivers, two tributaries of the Rio Madeira basin (Fig. 5). The presence of the new species within a conservation unit was confirmed from the records for Rio Roosevelt in the area of the Campos Amazônicos National Park (formerly known as: Marmelos Conservation Area BX044), located on the boundaries of the Amazonas and Rondônia States, Brazil.

Habitat.

The type locality of Myloplus zorroi is a moderately to rapidly flowing, clear-water river running over rocky and sandy bottoms (Fig. 6), with a depth ranging from approximately 2 m to at the most 8 m, and a mean width of 320 m. The river is surrounded by extensive riparian vegetation that is mainly composed of ombrophilous forest and is located at an elevation of approximately 78 m above sea level. Water flow in the main channel is significantly reduced during the dry season ( June–September), with most of the inflow restricted to small channels with rapids and extensive spread of rock outcrops scattered along the course of the main river. The records of Myloplus zorroi in Rio Roosevelt were collected close to the vegetated edge, while the specimens collected in Rio Aripuanã were made around the rapids of Corredeira dos Periquitos and Salto de Dardanelos.

Etymology.

The specific name ‘zorroi’ is dedicated to Mauricio Camargo-Zorro, a researcher at the Instituto Federal de Educação, Ciência e Tecnologia, in recognition of his invaluable contribution to the fish fauna inventory from the Marmelos Conservation Area. The name ‘zorroi’ also alludes to the Latin-American fictional character ‘Zorro’, which was the secret identity of Don Diego de la Vega, because the special features “masked” this fish as Tometes , concealing its true identity.