Myloplus tumukumak, Andrade & Jégu & Gama, 2018

Andrade, Marcelo C., Jégu, Michel & Gama, Cecile S., 2018, A new species of Myloplus Gill (Characiformes, Serrasalmidae) from the Tumucumaque Mountain Range, Brazil and French Guiana, with comments on M. rubripinnis, Zootaxa 4403 (1), pp. 111-122 : 112-117

Myloplus tumukumak , new species

( Figs. 1‒2 , and 4B)

Myloplus rubripinnnis (not Müller & Troschel): Jégu et al., 2004: 143 (in part; specimens from Oyapock River basin).

Holotype. ZMA 107.638 , 215.3 mm SL, Brazil, State of Amapá, Motoura River, a tributary of Oyapock River, 02°35’00”N 52°33’00”W, F. d’Aubenton , 11 Oct 1976.

Paratypes. Brazil, State of Amapá: IEPA 3547 , 1 , 136.0 mm SL, rio Amaparí, rio Araguari basin, Montanhas do Tumucumaque National Park , 01°35’45”N 52°29’32”W, C.S. Gama, 19 Sep 2004 . INPA 2262 , 1 , 254.5 mm SL, Nazay River, tributary of Oyapock River , F. d’Aubenton, 18 Apr 1984 . MNHN 1981-0541 , 1 , 152.0 mm SL, Motoura River , F. d’Aubenton, 11 Oct 1976 . French Guiana: IRSNB 20.223, 3, 43.9‒53.6 mm SL, Camopi River , Polydor, S.M. Léopold III & J.P. Gosse, 30 Nov 1969 . IRSNB 20.224, 2, 96.7‒97.1 mm SL, Oyapock River downstream Crique Adjoumba between Sikini and Camopi rivers, S.M. Léopold III & J.P. Gosse, 6 Dec 1969 . MNHN 1981-0423, 2, 67.4‒93.1 mm SL, Camopi River , Polydor, F. d’Aubenton, 19 Oct 1976 . ZMA 107.682 , 1 , 22.2 mm SL, Sikini Creek, Saut Couachim Tambe, near its confluence with Oyapock River , F. d’Aubenton, 26 Sep 1976 . ZMA 107.690, 2, 17.4‒19.6 mm SL, Armontabo Creek near its confluence with Oyapock River , F. d’Aubenton, 22 Oct 1976 .

Diagnosis. Myloplus tumukumak can be diagnosed from its congeners by having larger scales on flanks, resulting in lower scale counts. Myloplus tumukumak have 22‒26 circumpeduncular scale rows (vs. 38‒40 in M. arnoldi , 31‒41 in M. asterias , 34‒40 in M. lobatus , 29‒33 in M. lucienae , 30‒39 in M. rubripinnis , 34‒43 in M. rhomboidalis , 31‒34 in M. planquettei , 32‒38 in M. ternetzi , and 34‒36 in M. zorroi ). The new species is further diagnosed by having fewer scale rows below lateral line, i.e., 24‒29 (vs. 42‒45 in M. arnoldi , 40‒45 in M. asterias , 48‒56 in M. levis , 33‒42 in M. rubripinnis , 46‒57 in M. rhomboidalis , and 32‒37 in M. planquettei ). Myloplus tumukumak is additionally diagnosed by having 23‒25 branched dorsal-fin rays (vs. 18‒20 in M. arnoldi , 18‒19 in M. planquettei , 21‒22 in M. rhomboidalis , and 18‒21 in M. schomburgkii ). Myloplus tumukumak further differ from M. torquatus by having more branched anal-fin rays (35‒38 vs. 29‒30, respectively). Myloplus tumukumak is additionally diagnosed from M. lucienae , M. planquettei , and M. zorroi by having anteriormost spine of prepelvic serra reaching or surpassing anteriorly vertical through pectoral-fin origin ( Fig. 1B ) (vs. anteriormost spine in M. lucienae , M. planquettei , and M. zorroi never reaching vertical through pectoral-fin origin). Additional comments on diagnostic features of the new species are presented under the Discussion.

Description. Morphometric data in Table 1. Largest specimen examined 254.5 mm SL. Body deep and rounded, highest body depth at dorsal-fin origin. Snout blunt. Dorsal profile of head gently concave, predorsal profile slightly straight. Dorsal- and anal-fin bases slightly convex. Ventral profiles of head and body convex. Dorsal and ventral profiles of caudal peduncle convex.

Mouth terminal. Two interspaced rows of premaxillary teeth. Five*(14) molariform teeth in outer premaxillary row and 2*(14) in inner row. Dentary with 4(2), 5*(10), or 6(1) molariform teeth. Pair*(13) of teeth at dentary symphysis. Symphyseal tooth with anterior cutting edge. Maxilla edentulous.

Large cycloid scales on flanks. Lower flank scales somewhat larger than in upper flank. Perforated scales from supracleithrum to hypural plate end 56(1), 57(1), 59(5), 60*(2), 64(3), or 65(1); and total perforated scales on lateral line from supracleithrum to base of median caudal-fin rays 59(1), 61(1), 62(1), 63(3), 64(2), 65*(1), 67(2), 68(1), or 70(1). Longitudinal scale rows above lateral line to dorsal-fin origin 31(2), 32(4), 33(2), 34*(3), or 35(2); and longitudinal scale rows below lateral line to pelvic-fin origin 24(1), 25(4), 26(1), 27(3), 28*(3), or 29(1). Scale rows around caudal peduncle 22(1), 24*(3), 25(6), or 26(3).

Dorsal fin preceded by strong forward-directed spine. Dorsal-fin rays with ii*(14) unbranched, and 23(1), 24*(8), or 25(5) branched fin-rays. Anal-fin rays with ii(4) or iii*(10) unbranched, and 35(2), 36(1), 37*(8), or 38(3) branched fin-rays. Pectoral-fin rays with i*(12) unbranched, and 15(5), 16*(6), or 17(1) branched fin-rays. Pelvic-fin rays with i*(11) unbranched, and 6(9) or 7*(2) branched fin-rays. Adipose fin small, tear-drop shaped. Caudal fin forked into two equally-sized lobes.

Ventral keel serrae with well-developed spines. First anterior spine reaching or surpassing vertical through pectoral-fin origin ( Fig. 1B ). Prepelvic serra with 24(4), 25*(3), 26(3), 27(2), or 28(1) spines; postpelvic serra with 6(6), 7*(6), or 8(1) simple spines; and with 6*(6), 7(6), or 8(1) pairs of spines around anus. Total serra with 36(3), 38*(4), 39(1), 40(2), 41(2), or 42(1) spines. First branchial arch with 28(1) or 30(1) total gill rakers; upper branch with 13(1), or 15(1) rakers; lower branch with 14(2) rakers; and 1(2) at cartilage between upper and lower branches.

Neurocranium triangular, short anteroposteriorly, and with supraoccipital spine very high ( Fig. 1B ). Ascending premaxilla process elongated, massif, oblique anteroposteriorly, and well attached to neurocranium. Dentary short, with rectilinear lower surface. Five supraneurals, with 1 st and 5th supraneurals positioned anterior to neural spine of 4th and 8th centra, respectively. Nine predorsal vertebrae, 5 vertebrae between first anal-fin pterygiophore and last dorsal-fin pterygiophore, and 12 vertebrae posteriorly last dorsal-fin pterygiophore. First dorsal-fin pterygiophore inserted posterior of neural spine of 9th centra. First anal-fin pterygiophore inserted behind haemal spine of 22nd centra. Thirty-nine total vertebrae, with 21 precaudal and 18 caudal vertebrae ( Fig. 1B ).

Color in alcohol. Overall ground color uniformly yellowish brown ( Figs. 1A and 2 ). Ventral surface of head, belly and base of anal fin pale brown. Fins hyaline to brown, with distal portion of dorsal, anal and caudal fins pale gray. Outer portion of eyes dark yellowish-brown or predominantly black. Juveniles up to 90 mm SL present a faint humeral spot roughly positioned above lateral line, extending from 4th to 5th perforated scales of lateral line ( Fig. 2 ). Juveniles up to 22 mm SL with six to eight irregular blotches vertically elongated on head and flanks. First blotch located on head, and last blotch located on caudal peduncle end.

Sexual dimorphism. Mature males of M. tumukumak are recognized by the presence of an additional lobe on anal fin formed by the extension of the middle branched rays. An additional lobe on anal fin was found only in a mature male examined (INPA 2262). Conversely, juveniles and females present the first rays of anal-fin longer, forming a falcated lobe ( Fig. 2 ). No stiff hooks on distal-most lepidotrichia of anal-fin rays or filament extensions on dorsal-fin rays were found in the single examined mature male.

Growth and ontogeny. Body depth shifts from a low depth in specimens smaller than 45 mm SL (58% SL or less), to a deeper body in specimens larger than 45 mm SL (greater than 69% SL) ( Table 1). Embedded measurements in standard length, such as preanal and prepelvic lengths, pectoral to pelvic and pelvic to anal distances have a strong variation between smaller and larger specimens, having lower proportions in smaller specimens, with a gradual increase in proportional length along growth ( Table 1). The first dorsal- and anal-fin rays are very elongated in specimens around 50‒70 mm SL (mean 45.6% SL and 48.0% SL, respectively; see Fig. 2 ), compared with smaller specimens (mean 21.9% SL and 20.3% SL, respectively) and in specimens larger than 90 mm SL (mean 29.7% SL and 29.3% SL, for dorsal and anal fin, respectively). A positive allometry is evident in measurements related with body width, such as caudal peduncle width, and head measurements as interorbital distance, head, and mouth widths. There is a positive allometry of eye vertical diameter in specimens up to 45 mm SL (mean 41.1% HL), becoming isometric in specimens larger than 45 mm SL (mean 49% HL in specimens between 43.9‒136.0 mm SL), and presenting a negative allometry in specimens larger than 200 mm SL (mean 38.3% HL in two specimens).

The smaller specimens examined, around 20 mm SL, display molariform teeth with crown edge very high and spiky, while adult specimens present molariform teeth with crown edge low and rounded. Specimens smaller than 20 mm SL (ZMA 107.690) present premaxillary teeth with spiky crowns with a wide base as well as molariform teeth, whereas the dentary teeth are sharp and pointed, particularly the four posteriormost teeth, resembling caniniform teeth by presenting rounded base with general conical shape.

Distribution. Myloplus tumukumak is only known from the Oyapock River and its tributaries between Brazil and French Guiana, such as Nazay, Camopi, Sikini and Motoura rivers, and also occurring at the rio Amaparí, a tributary of rio Araguari basin, State of Amapá, Brazil ( Fig. 3 ). The new species occurs in rivers draining two Conservation Units, both lying at the eastern portion of the Tumuk-Humak mountain range, viz., the Parque Nacional Montanhas do Tumucumaque in Brazil, and the Parc Amazonien de Guyane in French Guiana.

Etymology. The specific epithet tumukumak refers to the Tumuk-Humak Mountain Range, where the new species occurs and, as far as known, from where it is apparently endemic. A toponymic adjective.

Figures

FIGURE 1. Myloplus tumukumak, ZMA 107.638, holotype, 215.3 mm SL, Motoura River, Oyapock River basin, State of Amapá, Brazil: photo (A) and x-ray (B), with yellow arrow indicating pectoral-fin origin, and white arrow the anteriormost spine of prepelvic serra.Scale bars = 10 mm.

FIGURE 2. Myloplus tumukumak, IRSNB 20.223, paratype, 45.9 mm SL, Camopi River, Oyapock River basin, French Guiana.Scale bar = 10mm.

FIGURE 3. Distribution map of Myloplus tumukumak (black circles; black star represent type locality), and Myloplus rubripinnis (whitecircles).The Tumuk-Humak MountainRange is represented ingray shade.Symbols can representmore than one record.