Oligosarcus amome, Almirón, Adriana, Casciotta, Jorge, Piálek, Lubomír, Doubnerová, Klára & Říčan, Oldřich, 2015

Almirón, Adriana, Casciotta, Jorge, Piálek, Lubomír, Doubnerová, Klára & Říčan, Oldřich, 2015, Oligosarcus amome (Ostariophysi: Characidae), a new species from the río Uruguay basin, Misiones, Argentina, Zootaxa 3915 (1), pp. 581-590 : 582-586

Oligosarcus amome , new species

( Fig. 1–7 , Table 1 )

Holotype. MLP 10679, 125.0 mm; Argentina: Misiones Province: río Uruguay basin, arroyo Oveja Negra, tributary of Arroyo Yabotí-Guazú, 27º08'15.5" S- 53º55'28.8" W, col: Casciotta et al., April 2010 ( Fig. 1 ).

Paratypes. MLP 10680, 6 ex. (1 ex. C&S), 112.3–121.4 mm; same data as holotype. MACN-ict 10374, 1 ex., 125.1 mm; Argentina: Misiones Province: río Uruguay basin: arroyo Fortaleza, tributary of the arroyo Yabotí- Guazú, 26º45'57.1" S – 54º10'51.7" W, col: Casciotta et al., November 2011.

Diagnosis: Oligosarcus amome differs from the remaining species of the genus except O. platensis and O. itau by the presence of two conspicuous series of teeth on the premaxilla.

Oligosarcus amome differs from O. platensis in having premaxillary teeth in the outer series pentacuspidate vs. tricuspidate; premaxillary inner series with five teeth penta to heptacuspidate vs. bi to pentacuspidate; ten to eleven maxillary teeth (uni to pentacuspidate) vs. 17 teeth (uni to tricuspidate); dentary teeth uni to heptacuspidate vs. uni to pentacuspidate; branched anal-fin rays 20 to 23 vs. 27; lateral line scales 39 to 41 vs. 44; and predorsal scales 14 to 16 vs. 24.

Oligosarcus amome differs from O. itau in having premaxillary teeth in the outer series pentacuspidate vs. tricuspidate; 39–41 vs. 41–42 lateral line scales, and 14–16 vs. 16–17 predorsal scales. The following morphometric characters also distinguish O. amome from O. itau : predorsal distance (51.4–53.5 vs. 54.7–57.0% SL); body depth (32.0–34.0 vs. 36.3–37.5% SL); pectoral-fin length (18.6–20.7 vs. 22.7–23.9% SL); pelvic-fin length (14.5–16.2 vs. 18.2–20.0% SL); pectoral to pelvic-fin distance (24.1–25.7 vs. 19.7–20.1% SL); head length (26.7–27.8 vs. 28.7–30.8% SL); peduncle depth (10.5–11.4 vs. 12.6–13.2% SL); peduncle length (10.5–12.0 vs. 14.9–16.0% SL); eye diameter (26.9–29.3vs. 31.6–33.2% HL); and snout length (27.5–29.9 vs. 23.9–24.6% HL).

Besides the presence of two series of teeth on the premaxilla, Oligosarcus amome is distinguished from O. brevioris , O. jacuiensis , O. jenynsii , and O. oligolepis , inhabiting the río Uruguay basin, by several characters. Oligosarcus amome is distinguished from O. brevioris , O. jacuiensis , and O. jenynsii by the number of circumpeduncular scales (17–18 vs. 21–23, 21–25, and 12–16 respectively), lateral line scales (39–41 vs. 47–56, 55–65, and 54–63 respectively), and ectopterygoid teeth (3 vs. 7–18, 10–20, and 12–16, respectively). Oligosarcus amome is clearly differentiated from O. oligolepis by the number of circumpeduncular scales (17–18 vs. 25–27), lateral line scales (39–41 vs. 72–79), and ectopterygoid teeth (3 vs. 14–16). Finally, Oligosarcus amome is different from O. pintoi in having 20–23 vs. 24–28 branched anal fin-rays; 10–11 vs. 15–23 maxillary teeth; 3 vs. 5–14 ectopterygoid teeth; and penta to heptacuspidate vs. all tricuspidate premaxillary teeth.

Description. Morphometric data of the holotype and seven paratypes are presented in Table 1 . Body elongate with maximum depth at dorsal-fin origin (32.0–34.0% SL). Dorsal profile slightly convex from tip of snout to nares, straight to tip of supraoccipital process; convex to dorsal-fin origin; almost straight from this point to caudal peduncle; slightly concave along caudal peduncle to base of caudal-fin rays ( Fig. 1 ). Ventral profile of body gently convex from dentary tip to anal-fin origin; straight along base of anal fin, and slightly concave under caudal peduncle.

Dorsal-fin origin just posterior to middle standard length (predorsal distance 51.4–53.5% SL). Pelvic-fin origin placed anterior to vertical through dorsal-fin origin. Anal-fin origin placed behind at vertical through base of posteriormost dorsal-fin rays. Tip of pectoral fin not reaching pelvic-fin origin; tip of pelvic fin not reaching analfin origin.

Mouth terminal, tip of maxilla reaching posteriorly to middle of orbit. Premaxilla bears two series of teeth. Outer row with 4 (7*) 5 (1) pentacuspidate teeth, with large central cusp and very small lateral ones. Inner row with 5 (7*), 6 (1) narrow teeth with a central cusp well developed, and lateral cusps smaller; symphyseal tooth slender and long, with 5–6 cusps; second, third and fourth tooth with 7 cusps; and fifth tooth with 5–6 cusps ( Fig. 2 ). Maxilla rather long, with 10–11 conical, tri or pentacuspidate teeth ( Fig. 2 ). Dentary with 4–5 heptacuspidate teeth followed by 1 pentacuspidate and 8 to 10 smaller tricuspidate or conical teeth ( Fig. 3 ). Lateral cusps of dentary teeth much smaller than medial ones. Ectopterygoid with 3 teeth.

Eye as long as snout. Third infraorbital not contacting laterosensory canal of preopercle.

Dorsal-fin rays iii,9 (first ray visible only in C&S specimen); distal margin of dorsal fin straight, with last unbranched and first branched dorsal-fin rays longest. Anal-fin rays iii-v,20(2), 21(1*), 22(4), or 23(1), C&S specimen with five unbranched rays. Caudal fin with principal rays i,17,i. Pectoral-fin rays i,12(2*),13(6). Pelvicfin rays ii,7(5*) or 8(2), first ray visible only in C&S specimen. Membranous flaps on dorsal and anal fin in both sexes, pelvic fin with flaps only in males.

Scales cycloid. Lateral line complete with 39(1), 40(5*) or 41(2) perforated scales. Scales between dorsal-fin origin and lateral line 8(7*) or 9(1); scales between lateral line and pelvic-fin origin 5(3*), 5½ (4), or 6(1). Scales around caudal peduncle 17(5*) or 18(3). Predorsal scales 14*–16. One row of 9–15 scales forming a sheath covering base of anterior (9 to 12) anal-fin rays.

First branchial arch with 20 gill rakers: 7 on epibranchial, 1 on cartilage, 10 on ceratobranchial, and 2 on hypobranchial; posterior edge of first epibranchial with a second row of 4 gill rakers. Thirty-five vertebrae. Seven supraneurals. Caudal fin with 12 dorsal and 10 ventral procurrent rays (1 ex., C&S).

Sexual dimorphism. Males with hooks on last unbranched and first 9 branched anal-fin rays. Hooks on posterior branch of rays, one pair per segment. Males bearing hooks on second to fifth pelvic-fin rays, one pair per segment.

Colour in life. Body silvery yellow, dark grey dorsally. Lateral band faint. Two vertically elongated humeral spots, anterior one well defined and posterior one faint. Black caudal spot horizontally elongated, extends backwards on median caudal-fin rays to the end of caudal fin. Dorsum of head, snout, maxilla, and dentary, dark grey. Cheek and opercle silvery yellow with small scattered chromatophores. Dorsal and ventral region of eye, red. Anal fin deep yellow, red on anterior lobes from first unbranched to fourth branched rays. External lobes of caudal fin red, medial rays orange, central rays black. Dorsal, pectoral, and pelvic fins, yellow with scattered red and dark chromatophores. Adipose-fin hyaline with scattered dark grey chromatophores ( Fig. 4 ).

Colour in alcohol. Body yellowish, darker dorsally. Dorsum of head, premaxilla and tip of dentary dark. Scattered chromatophores on maxilla, cheek, and opercle. Scales from upper half of flank darker. Scales on flanks with chromatophores concentrated on posterior margin, giving a reticulated aspect. First humeral spot vertically elongated, situated just behind the opercular membrane. A second spot, very faint, vertically elongated, placed three scales behind the first one. A dark wide lateral band on flank extended from anterior humeral spot to end of middle caudal-fin rays. Dark and subcircular caudal spot placed at the end of caudal peduncle. Pectoral and pelvic fins hyaline; dark scattered chromatophores on pectoral-fin rays. Dorsal fin hyaline with dark scattered chromatophores on rays and flaps. Adipose fin hyaline with dark scattered chromatophores on its surface. Anal fin hyaline with chromatophores on distal edge of rays and membranes forming a narrow band. Caudal fin hyaline with dark middle caudal-fin rays; scattered chromatophores on distal edge of rays and membranes.

Distribution. Oligosarcus amome is only known from the arroyos Oveja Negra ( Fig. 5 ) and Fortaleza, both tributaries of the arroyo Yabotí-Guazú, río Uruguay basin in Yabotí Biosphere Reserve in Misiones, Argentina ( Fig. 6 ).

Etymology. The species epithet amome is a Guaraní word that means once in a while, rare, in references to the low occurrence of the specimens of this species in the localities where they were captured.

Systematics. The phylogenetic analysis of the 166 taxa and 366 character matrix resulted in a large number of MP trees. The strict consensus of 5000 MP trees is shown in Fig. 7 . The shortest MP trees had a length of 2173 steps, a consistency index of 0.18 and a retention index of 0.67. Oligosarcus amome is the sister taxon of all remaining analyzed species of the genus excepting O. itau . The Central American Bramocharax bransfordii is the sister group of Oligosarcus in this morphological phylogeny. The successive sister groups of this clade are two species of the polyphyletic Bryconamericus ( B. scleroparius and B. emperador ), and the genera Markiana ( M. nigripinnis ) and Astyanacinus ( A. moorii ). This monophyletic group which includes Oligosarcus is nested inside the paraphyletic Astyanax , which further includes one species of the polyphyletic Hyphessobrycon ( H. anisitsi ) and Psellogrammus kennedyi .

Figures

FIGURE 1. Oligosarcus amome, female, holotype, MLP 10679, 125, 0 mm; Misiones Province, río Uruguay basin, arroyo Oveja Negra, tributary of arroyo Yabotí-Guazú.

FIGURE 2. Oligosarcus amome, MLP 10680, 119.0 mm SL, medial view of left upper jaw. Scale bar: 1 mm.

FIGURE 3. Oligosarcus amome, MLP 10680, 119.0 mm SL, medial view of right lower jaw. Scale bar: 1 mm.

FIGURE 4. Oligosarcus amome, live specimen, MACN-ict 10374, paratype, female, 125.1 mm SL, Argentina, Misiones Province, río Uruguay basin, arroyo Fortaleza, tributary of the arroyo Yabotí-Guazú.

FIGURE 5. Oligosarcus amome, type locality, Argentina, Misiones Province, arroyo Oveja Negra, tributary of arroyo Yabotí- Guazú, 27 º 08 ' 15.5 " S- 53 º 55 ' 28.8 " W.

FIGURE 6. Hydrological map of the Misiones Province, Argentina showing the sampling sites. 1. arroyo Fortaleza, 2. arroyo Oveja Negra (type locality). Both streams are tributaries of arroyo Yabotí-Guazú.

FIGURE 7. Strict consensus of 5000 + maximum parsimony trees from phylogenetic analysis of 165 taxa plus outgroup and 366 morphological characters of the Characidae and selected Characoidei. The genus Oligosarcus is highlighted and the new species is underlined.

Tables

TABLE 1. Oligosarcus amome n. sp. Morphometrics of holotype and seven paratypes. Standard lengths are expressed in mm. SD: standard deviation.

	Holotype	range	X	SD
Standard length	125.0	112.3–125.1
% of standard length
Predorsal distance	51.8	51.4–53.5	52.3	0.76
Preanal distance	65.7	65.7–67.5	66.4	0.63
Preventral distance	48.2	48.2–50.4	49.2	0.98
Body depth	34.0	32.0–34.0	33.3	0.80
Dorsal-fin base	13.3	12.6–13.7	13.2	0.34
Anal-fin base	25.4	24.0–28.9	26.1	1.42
Pectoral-fin length	18.6	18.6–20.7	19.5	0.64
Pelvic-fin length	16.1	14.5–16.2	15.7	0.58
Pectoral to pelvic-fin distance	24.9	24.1–25.7	24.8	0.56
Pelvic to anal-fin distance	19.8	18.0–20.7	19.2	0.89
Head length	26.7	26.7–27.8	27.0	0.41
Peduncle depth	10.8	10.5–11.4	10.9	0.35
Peduncle length	11.4	10.5–12.0	11.3	0.51
% head length
Eye diameter	26.9	26.9–29.3	27.8	0.99
Interorbital width	30.5	29.4–31.3	30.5	0.74
Postorbital distance	47.6	47.3–50.0	48.6	0.98
Snout length	29.9	27.5–29.9	28.9	0.96
Maxillary length	27.2	26.2–28.4	27.5	0.86
Upper-jaw length	43.7	43.1–45.2	44.4	0.89