Moenkhausia restricta, Soares & Benine, 2019

Soares, Nathália C. & Benine, Ricardo C., 2019, Moenkhausia restricta, a new species from the upper Rio Negro, Amazon basin, northwestern Brazil (Characiformes: Characidae), Zootaxa 4700 (4), pp. 487-493 : 488-491

Moenkhausia restricta , new species

( Tab. 1 , Figs. 1 , 3 , 4b ;)

Holotype. MZUSP 125291 , 39.9 mm SL, Brazil, Amazonas, São Gabriel da Cachoeira, Rio Miuá (trib. Rio Negro ), 00°06’31”S 66°52’58”W; C. Oliveira, M. I. Taylor and M. Alexandrou, 14 August 2008.

Paratypes. LBP 7066, 10, 3 C&S, 35.2–44.4 mm SL; MZUSP 125292 , 2 , 41.0– 41.2 mm SL ; ZUEC 17134 , 2 , 35.3–39.3 mm SL, same data as holotype .

Diagnosis. Moenkhausia restricta can be diagnosed from all congeners by the combination of presence of 12 transverse scale rows (seven above and five below lateral line) and a low body depth (30.4–33.0% SL). Additional characters allowing the diagnosis of M. restricta from its congeners is the combination of presence of a single conspicuous vertically elongated humeral blotch, and a conspicuous caudal peduncle blotch extending to the distal margin of the median caudal-fin rays. Moenkhausia restricta is more similar among non-congeners to Jupiaba zonata , with which it shares a similar color pattern but from which it differs by having small scales covering the base of the caudal-fin (absent in J. zonata ) and by not bearing pelvic spines (present in J. zonata ).

Description. Morphometric data summarized in Table 1 . Largest specimen examined 44.4 mm SL. Body elongated, greatest body depth at dorsal-fin origin. Dorsal profile of head slightly convex from tip of snout to posterior margin of frontal bone; straight or slightly concave from this point to tip of supraoccipital spine; convex from tip of supraoccipital spine to end of dorsal-fin base; straight or slightly convex from this point to end of adipose-fin. Caudal peduncle dorsal profile slightly concave. Ventral profile of body convex from tip of lower jaw to interopercle bone; straight or slightly convex from this point to origin of pelvic-fin; straight from this point to origin of anal-fin; anal-fin base posterodorsally slanted. Caudal peduncle ventral profile slightly concave.

Mouth terminal. Premaxillary teeth arranged in two rows; outer row with 4*(13) or 5(2) tricuspid teeth, median cusp more pronounced than remaining cusps. Inner row with 5 pentacuspid teeth, median cusp more pronounced than remaining cusps. Maxillar with 2*(10) or 3(5) teeth with one to five cusps. Dentary with 4 large pentacuspid teeth, followed by a series of very small teeth with one to three cusps ( Fig. 2 ).

Dorsal-fin rays ii, 9* (15); anal-fin rays iv (3 c&s), 23 (1), 24 (6), 25* (6), 26 (2); pectoral-fin i, 11* (4), 12 (10), 13 (1); pelvic-fin rays i,7* (14). Origin of dorsal and pelvic-fins vertically aligned. Distal tip of adpressed pectoral-fin rays not reaching origin of pelvic fin; distal tip of adpressed pelvic-fin rays not reaching origin of anal fin. Caudal fin forked.

Scales cycloid with straight somewhat parallel radii; one or two radii more evident in each scale; circulli concentric and slighthly marked. Predorsal scale series irregularly arranged. Lateral line complete, with 36(1), 37(4), 38(8), or 39*(2) scales. Scale rows between lateral line and origin of dorsal-fin 7*(15). Scale rows between lateral line and origin of pelvic-fin 5*(15). Scale rows around caudal peduncle 13(3), 14*(9), or 15(3). Small scales covering anterior third of caudal-fin lobes.

First gill arch with 8*(9) or 9(5) gill rakers on upper limb and 14*(6) or 15(8) gill rakers on lower limb. Vertebrae 36 (1). Supraneurals 5 (2).

Color in alcohol. Overall ground color of head and body light brown ( Fig. 1 ). Dorsal portion of head beige. Field of dark chromatophores covering snout, both lips and superior third of maxilla. Ventral portion of head clearbrown. Infraorbitals and opercular series beige. Dark dorsal midline, from tip of supraoccipital to first ray of dorsal fin. Single conspicuous dark humeral blotch above lateral line, irregularly shaped, occupying three scales length and two scales height; slightly conspicuous extension vertically along two or three scales, including lateral line. Dorsal half of humeral mark wider and more densely pigmented. Anterior and posterior margins of humeral blotch clear. Longitudinal silvery stripe along body midline, faint and narrow, beginning two scale rows spaced after humeral blotch and extending to caudal peduncle. Overall color of dorsal portion of body darker than ventral portion, with longitudinal stripe clearly delimiting the color gradient. Caudal-peduncle blotch dark, roughly rounded in shape, and densely pigmented, extending over the distal portion of caudal peduncle to base of principal caudal-fin rays. Sparse dark pigmentation extending along median caudal-fin rays. Dorsal and anal fins slightly pigmented along distal margins. Paired fins with few sparse dark chromatophores, more so on unbranched rays. Caudal-fin densely pigmented at base and medial rays; few sparse dark chromatophores at distal portion of rays. Adipose-fin sparsely pigmented, more so along its distal border.

Sexual dimorphism. Secondary sexual characters were not found in the examined specimens of Moenkhausia restricta .

Geographic distribution. Moenkhausia restricta is only known from the type-locality, the Rio Miuá, a tributary of the upper Rio Negro, Amazon basin, Amazonas, Brazil ( Fig. 3 ).

Etymology. The specific name restricta is from Latin meaning tight, limited, in reference to the uncommon high number of transversal scale rows in a somewhat shallow-bodied species. An adjective.

Comments. As already mentioned in the Introduction, Moenkhausia restricta was collected along with J. zonata , with which it probably forms mixed shoals. The exceptional body shallowing in a species with a great number of transverse scale rows could be interpreted as evidence of convergence between M. restricta and J. zonata ( Fig. 4 ). Indeed, among the somewhat shallow bodied species of Jupiaba , only J. zonata has such a high number of scales, and such morphological convergence may be indicative of some ecological and adaptive interaction. Zanata et al. (2009) were the first authors to provide a discussion on the ecology of such interactions. These authors interpreted as a putative case of Batesian mimicry between the supposedly mimic Moenkhausia pirauba Zanata, Birindelli and Moreira , and its purported models Jupiaba apenima Zanata , and J. yarina Zanata , considering the retrorse pelvic spine of Jupiaba as an anti-predatory device. Moenkhausia pirauba occurs in sympatry with Jupiaba apenima in the Rio Tapajós and Rio Xingu, and with J. yarina in the Rio Arinos, presenting the same coloration variation of its putative models, reinforcing the mimicry hypothesis, with an added polymorphic aspect of such interaction ( Zanata et al. 2009). These authors also discussed another putative case of Batesian mimicry among Astyanax anterior (mimic) and different species of Jupiaba ( J. abramoides , J. anteroides , and J. poranga ) (models) in tributaries of the Rio Teles Pires and upper Rio Negro (Rio Tiquié). Further discussion on Jupiaba and Batesian mimicry was also provided by Marinho and Birindelli (2013), describing the interaction between Astyanax multidens with J. paranatinga and J. cf. essequibensis . Therefore, we herein hypothesized that Moenkhausia restricta presents this same type of interspecific interaction, reinforcing the putative ecological advantage of bearing pelvic spines.

Comparative material examined. Jupiaba zonata . MZUSP 29465, 23, 28.2–38.9 mm SL, Brazil, Amazonas, Rio Negro. MZUSP 29471, 31, 30.5–35.0 mm SL, Brazil, Amazonas, Rio Negro; MZUSP 109506, 19, 32.9–38.2 mm SL, Brazil, Amazonas, Santa Isabel do Rio Negro, Rio Negro; LBP 16924, 10, 35.8–43.3 mm SL, Brazil, Amazonas, São Gabriel da Cachoeira, Rio Negro. Jupiaba keithi . LBP 21122, 1, 41.6 mm SL, Brazil, Amapá, Rio Oiapoque. Jupiaba meunieri . MZUEL 9290, 2, 42.1– 47.2 mm SL. Brazil, Mato Grosso, Brasnorte, Rio Tapajós, Rio Juruena basin; LBP 21007, 3, 62.4–66.9 mm SL, Brazil, Amapá, Rio Calçoene. Moenkhausia surinamensis . LBP 21169, 13, 33.9–51.0 mm SL, Brazil, Amapá, Rio Oiapoque.

Figures

FIGURE 1. Holotype of Moenkhausia restricta, MZUSP 125291, 39.9 mm SL, Brazil, Amazonas, São Gabriel da Cachoeira, Rio Negro basin.

FIGURE 2. Medial view of left side of upper and lower jaws of Moenkhausia restricta, LBP 7066, paratype, 39.3 mm SL. a. left maxilla, b. left premaxilla and c. left dentary. Scale bar = 1 mm.

FIGURE 3. Map of northwestern Amazon basin showing the type locality of Moenkhausia restricta (yellow star).

FIGURE 4. a) Jupiaba zonata, LBP 16924, 38.1 mm SL; and b) Moenkhausia restricta LBP 7066, 40.2 mm SL.