Tetragonopterus ommatus, Silva, Gabriel S. C., Melo, Bruno F., Oliveira, Claudio & Benine, Ricardo C., 2016

Silva, Gabriel S. C., Melo, Bruno F., Oliveira, Claudio & Benine, Ricardo C., 2016, Revision of the South American genus Tetragonopterus Cuvier, 1816 (Teleostei: Characidae) with description of four new species, Zootaxa 4200 (1), pp. 1-46 : 38-40

Tetragonopterus ommatus , new species

Fig. 14 , Table 8

Tetragonopterus sp. Tapajós: Melo et al., 2016: 709 –717 (molecular phylogeny).

Holotype. MZUSP 92667, 64.1 mm SL, Brazil, Pará, Itaituba, Rio Tapajós , 4°21’34”S 56°10’03”W, L. Souza & J. Birindelli, 0 8 Nov 2006.

Paratypes. All from Brazil: LBP 13949, 3, 62.8–65.9 mm SL, Pará, Itaituba, Rio Tapajós , 4°27’29.5”S 56°16’03”W, R. Britzke et al., 25 Sep 2011 . LBP 16126, 1, 47.6 mm SL, Pará, Itaituba, Rio Tapajós, 4°33’09.7”S 56°17’59.6”W, R. Britzke et al., 11 Jun 2012 .

Diagnosis. Tetragonopterus ommatus is distinguished from all congeners by the presence of 7–8 maxillary teeth (vs. 1–6) and by having a dark, vertically-oriented patch of dark pigmentation limited to the posterior portion of the caudal peduncle (vs. mark centered on the caudal peduncle). Tetragonopterus ommatus also differs from T. anostomus , T. denticulatus and T. kuluene by having 4 principal teeth on dentary (vs. 5–6) and by having more robust dentary teeth (vs. thinner and sharper teeth). Tetragonopterus ommatus differs from T. anostomus by having a terminal mouth (vs. subsuperior mouth) and by having two conspicuous humeral marks (vs. only one humeral mark). In addition, T. ommatus differs from T. anostomus and T. araguaiensis by the number of gill rakers on the lower (13–15) and upper (8–9) limbs of the first gill arch (vs. 17–20 and 10–12). Tetragonopterus ommatus is distinguished from T. argenteus by having 8 predorsal scales (vs. 11–17). It differs from T. carvalhoi by the presence of a rounded dark mark on the caudal peduncle (vs. a lozenge-shaped dark mark on the caudal peduncle). Tetragonopterus ommatus differs from T. rarus and T. georgiae by the presence of 3.5 scale rows between lateral line and pelvic-fin origin (vs. 4.5–5.5). Finally, T. ommatus differs from T. rarus by the absence of dark longitudinal stripes on the trunk (vs. presence of stripes).

Description. Morphometric data presented in Table 8. Body compressed and moderately elongate when compared with congeners. Greatest body depth at dorsal-fin origin. Dorsal profile slightly convex from snout tip to vertical through middle of orbit; straight from this point to end of occipital process; convex from that point to dorsal-fin origin; straight or slightly convex along dorsal-fin base to rear of adipose fin. Prepelvic region transversely flattened with distinct, longitudinally aligned lateral keels. Ventral profile slightly convex from lower lip to anal-fin origin; straight along base of anal fin. Caudal peduncle with concave dorsal and ventral profiles.

Snout shorter than orbital diameter. Mouth terminal. Upper and lower jaw of similar size. Premaxillary teeth in two rows of relatively small teeth with sharp cusps. Outer row with 6 (1) or 7 (4)* teeth with three cusps, central cusp slightly longer. Inner row with 5 (4)* or 6 (1) teeth with four or five cusps, central cusp, when present, twice as long as the lateral cusps. Maxilla with 7 (1)* or 8 (4) teeth with three cusps. Dentary bearing 4 (5)* anteriormost teeth with four or five cusps.

Dorsal-fin rays ii,9 (5)*. First unbranched ray shorter than second one. Dorsal-fin origin at middle of the body in SL. Distal margin of fin straight with anterior rays longer. Anal-fin rays v,25 (2) or v,26 (3)*; posterior unbranched rays and anterior branched rays slightly longer than following rays. Anal-fin origin at vertical through two or three scales posterior to last branched dorsal-fin ray. Pelvic-fin rays i,7 (5)*. Pelvic-fin origin located at vertical through dorsal-fin origin. Distal margin of pelvic-fin angled, anterior rays longest. Tip of adpressed pelvic fin not reaching the anal-fin origin. Pectoral-fin rays i,14 (2)*or i,15 (3). Caudal fin forked with i,16,i principal rays (three radiographed adults).

Scales large and cycloids. Lateral line complete and distinctly bent downward anteriorly. Longitudinal scales 30 (3) or 31 (2)*. Scale rows between lateral line and dorsal-fin origin 6 (5)*. Scale rows between lateral line and pelvic-fin origin 3.5 (5)*. Predorsal scales 8 (5)*. Scale rows around caudal peduncle 12 (1), 13 (3)* or 14 (1). Anal-fin base covered by a single row of small scales. Lobes of caudal fin poorly scaled.

First gill arch with 8 (3)* or 9 (2) rakers on upper limb and 13 (2)*, 14 (2) or 15 (1) rakers on lower limb. Total vertebrae 30 (3 radiographs), precaudal vertebrae 12, intermediate vertebrae 2, and caudal vertebrae 16 (3 radiographs). Supraneurals 3 (3 radiographs).

Holotype Range Mean Standard length (mm) 64.1 47.6–65.9 61.2 Percentages of standard length

Greatest depth 42.2 42.1–44.7 43.5 Predorsal length 50.2 50.2–52.7 50.9 Prepectoral length 31.0 30.8–33.8 31.7 Prepelvic length 51.8 51.8–55.5 53.2 Preanal length 69.9 69.9–73.9 71.4 Caudal peduncle depth 9.36 9.22–10.2 9.71 Caudal peduncle length 9.16 9.03–10.7 9.62 Pectoral-fin length 24.2 24.2–25.5 24.9 Pelvic-fin length 18.5 18.5–20.9 19.8 Dorsal-fin length 31.1 31.1–36.1 33.6 Length of dorsal-fin base 15.7 15.6–17.9 16.5 Anal-fin length 15.9 15.4–19.5 16.4 Length of anal-fin base 29.2 28.4–30.3 29.0 Distance from eye to dorsal-fin origin 46.3 45.9–48.5 46.7 Distance from dorsal-fin origin to caudal-fin base 53.2 51.6–57.4 54.8 Head length 32.6 32.0–35.3 33.1 Head depth 24.6 24.0–27.3 25.2 Percentages of head length

Snout length 18 18–22 20.2 Maxillary length 46 46–50 48.5 Horizontal orbital diameter 51 49–52 50.6 Least interorbital width 28 25–30 27.9 Color in alcohol. General body color pale brown. Dorsal portions of head and body darkly pigmented. Opercular and infraorbital bones silvery. Dorsolateral portion of body with few chromatophores along distal margins of scales. Ventrolateral portion of body unpigmented. Two vertical dark humeral marks spaced by one scale row, with anterior more evident. Anterior humeral mark extending over three horizontal scale rows above lateral line. Posterior humeral mark extending over three horizontal scale rows above lateral line. Caudal peduncle with a ventrally-oriented patch of pigmentation limited to posterior portion of caudal peduncle. Midlateral silvery stripe broad, extending from supracleithrum to caudal peduncle. Anal, pelvic, and dorsal fin hyaline outlined by small chromatophores at distal portions of rays. Adipose fin hyaline ( Fig. 14 ).

Sexual dimorphism. Adult males with bony hooks on distal segments of the first 12 branched rays of the anal fin. Two bony hooks per segment.

Distribution. Tetragonopterus ommatus is only known near the Cachoeira de São Luiz, middle Rio Tapajós, municipality of Itaituba, Pará Brazil ( Fig. 2 b).

Etymology. The name ommatus is from Greek omma meaning eye, in reference to the great diameter of the orbits observed in this species.

Figures

FIGURE 14. Tetragonopterus ommatus. MZUSP 92667, holotype, 61.1 mm SL, Brazil, Pará, Itaituba, Rio Tapajós, Amazon basin.