Moenkhausia pankilopteryx, Vinicius A. Bertaco & Paulo H. F. Lucinda, 2006

Vinicius A. Bertaco & Paulo H. F. Lucinda, 2006, Moenkhausia pankilopteryx, new species from rio Tocantins drainage, Brazil (Ostariophysi: Characiformes, Characidae)., Zootaxa 1120, pp. 57-68 : 59-66

Moenkhausia pankilopteryx , new species

(Figs. 1-3; Table 1)

Holotype. MZUSP 88258 (82.8 mm SL, male), Brazil: Pará: rio Itacaiunas (rio Tocantins drainage), about 10 km east of road N -4, Serra dos Carajás at Igarapé, approx. 05º52’S, 50º32’W, M. Goulding, 13 Oct 1983.

Paratypes. Brazil: Pará: rio Tocantins drainage: MCP 38716 (15, 2 c&s, 69.2-93.2 mm SL) , MZUSP 29931 (2, 75.0-94.3 mm SL) , MZUSP 51999 (44, 70.3-94.1 mm SL), collected with the holotype . MZUSP 30289 (10, 51.6-96.7 mm SL), rio Itacaiunas, Caldeirão, Igarapé do Pojuca, approx. 05º52’S, 50º32’W, M. Goulding, 15 Oct 1983 . Tocantins: UNT 2445 (2, 59.6-66.9 mm SL), sítio Estrela, Silvanópolis, approx. 11º09’S 48º10’W, A. L. G. Borges, 11 May 1996 . UNT 2034 (1, 64.8 mm SL) and UNT 2035 (1, 64.9 mm SL), córrego Albano, near mouth of the rio Paranã, Paranã, approx. 12º34’S 48º06’W, NEAMB -UFT, 9 Dec 1998 .

Diagnosis. Moenkhausia pankilopteryx is distinguished from its congeners primarily by the putative autapomorphic presence of bony hooks on all fins of mature males. It is further distinguished from nearly all other members of the genus by the combination of 37-41 pored scales in the lateral line; a caudal-peduncle spot; a deep body, 43.3-51.0 % SL; two humeral spots, of which the first is black, larger and vertically elongate, and the second is dark, very diffuse, and not always visible; two to three maxillary teeth, and analfin rays ii -iv, 24-27 (see Discussion section for additional details).

Description. Morphometric data are summarised in Table 1. Body deep, the greatest body depth anterior to dorsal-fin origin. Dorsal profile of head straight or slightly concave. Profile convex from supraocciptal tip to base of last dorsal-fin ray, and straight towards adipose-fin origin. Ventral profile of head convex. Ventral body profile slightly convex to nearly straight from pectoral-fin origin to pelvic-fin origin, and straight to slightly convex towards anal-fin origin. Body profile along anal-fin base posterodorsally slanted. Caudal peduncle short, nearly straight to slightly concave along dorsal and ventral margins.

Snout rounded from margin of upper lip to vertical through anterior nostrils. Head small. Mouth terminal. Maxilla extending anteriorly to below center of orbit, slightly curved, and aligned at an angle of approximately 45 degrees to longitudinal body axis. Anterodorsal border of maxilla concave and posterodorsal border slightly convex, and the anteroventral and posteroventral borders convex. Maxilla slightly widened posteriorly.

Two tooth rows on premaxilla; outer row with three or five tricuspid or pentacuspid teeth, with central cusp longer; inner row with five pentacuspid or heptacuspid teeth, and with central cusp two or three times longer and broader than other cusps; teeth gradually decreasing in length from first to fourth tooth. Maxilla with two or three (usually two) tricuspid or pentacuspid teeth, with central cusp longest. Four or five anteriormost dentary teeth largest, with seven cusps, followed by one or two teeth (6-7) of medium size with 5- 6 cusps, and next three teeth (8-10) with one to three cusps. Central cusp in all teeth two or three times longer and broader than other cusps. All cusp tips slightly curved posteriorly towards inside of mouth (Fig. 3).

Dorsal-fin rays ii, 9 (n = 25), the first unbranched ray approximately one-half length of second ray. Dorsal-fin origin located posterior to middle of body (tip of snout to base of caudal fin) and posterior to vertical through pelvic-fin origin. Dorsal-fin rays of males bearing one or two pairs of small retrorse bony hooks along posteroventral border of each lepidotrichial segment, usually between first and eighth branched rays, and located along posteriormost branch and on distal third length of each ray. Adipose-fin located approximately at vertical above insertion of base of 22nd-24th anal-fin rays.

Anal-fin rays ii-iv, 24-26 (rarely 27, mean = 25.6, n = 25). First unbranched ray visible only in cleared and stained specimens. Anal-fin profile smoothly concave in females, and nearly straight in males. Anal-fin origin posterior to vertical through base of last dorsal-fin ray. Anal-fin rays of males bearing one pair of small, elongate, retrorse bony hooks along posterolateral border of each segment of lepidotrichia, usually along last unbranched ray and 20th branched rays; hooks more numerous along second through seventh branched rays. Hooks usually located along posteriormost branch and distal half to two-thirds length of each ray.

Pectoral-fin rays i, 11-12 (mean = 11.6, n = 25). Pectoral-fin tip not reaching pelvicfin origin in either sex. Pectoral-fin rays of males bearing one or two pairs of small retrorse bony hooks along posteroventral border of each lepidotrichial segment, usually along first and eighth branched rays, and located along posteriormost branch and on distal third of length of each ray. Pelvic-fin rays i, 7 (n = 25). Pelvic-fin origin located anterior to vertical through dorsal-fin origin. Pelvic fin of males usually bearing one retrorse bony hook per lepidotrichia along ventromedial border of second to fourth branched rays. Hooks usually located along posteriormost branch and distal half to two-thirds of length of each ray. Caudal-fin forked, with 19 principal rays; dorsal lobe procurrent rays 11-13 (n = 2), and ventral procurrent rays 10-11 (n = 2).

Scales cycloid, and moderately large. Lateral line complete. Scales in longitudinal series 37-41 (mean = 39.3, n = 25). Scale rows between dorsal-fin origin and lateral line 7-8 (mean = 7.9, n = 25); scale rows between lateral line and pelvic-fin origin 6-7 (mean = 6.3, n = 25). Predorsal scales 11-14, arranged in regular series (mean = 12.2). Scale rows around caudal peduncle 16. Scale sheath along anal-fin base 12-16 scales in single series, extending to base of tenth to fifteenth branched rays. Small scales on base of caudal fin.

Precaudal vertebrae 15-16; caudal vertebrae 19; total vertebrae 34-35. Supraneurals 4. Gill rakers on dorsal limb of outer gill arch 9, and on ventral limb 13-14 (n = 2).

Colour in alcohol. Dorsal and dorsolateral portion of head and body dark brown. Two humeral spots, the first black and narrow, large and vertically elongate, located over second to fourth lateral-line scale and extending over six or seven horizontal series of scales, including lateral line; second humeral spot dark and very diffuse, located on first series of scales above lateral line, between sixth to eighth series of scales and extending over two or three horizontal series of scales. Second humeral spot not visible in some specimens. Midlateral body with dark narrow stripe extending from humeral region to caudal-peduncle. Black spot on caudal peduncle extending over middle caudal-fin rays. Remaining fins lacking distinctive areas of pigmentation (Fig. 2).

Sexual dimorphism. Mature males of M. pankilopteryx are easily recognised by the presence of bony hooks on all fin rays. Males and females also differ slightly with regard to pectoral and pelvic-fin lengths (Table 1). Mature gonads were found on the two dissected cleared and stained specimens (MZUSP 51999, male 73.9 mm SL, female 74.7 mm SL).

Distribution. Moenkhausia pankilopteryx is known from the rio Tocantins drainage, Brazil (Fig. 1).

Etymology. The specific name, pankilopteryx, is from the Greek, pan (all), ankilos (hooked), and pteryx (fins), in reference to the presence of hooks on all fins in males.

Discussion.

Moenkhausia is an ill-defined and presumably artificial assemblage of species that has long served as a “catch-all” genus for small characids bearing scales on the base of the caudal fin and a complete lateral line.

The definition of a monophyletic Moenkhausia has been addressed and discussed on numerous occasions (e. g. Fink, 1979; Géry, 1977; 1992; Costa, 1994; Weitzman & Palmer, 1997; Lucena & Lucena, 1999; Lima & Toledo-Piza, 2001; Benine, 2002), but as yet there has been no satisfactory resolution to this problem. The above authors have discussed the likely relationships of species referred to Moenkhausia to species of the genera Gymnocorymbus Eigenmann , Hyphessobrycon Durbin , and Hemigrammus Gill . The monophyly of Moenkhausia remains in question and elucidation of the relationships of its included species necessarily involves resolution of the relationships among the species of other characid genera, especially the three mentioned immediately above (i.e. Gymnocorymbus , Hyphessobrycon , and Hemigrammus ). However, such discussion is beyond the scope of this paper.

The situation is further complicated by numerous undescribed species that fit the current definition of the genus (see below). Given these circumstances, one may question the wisdom of describing a new species of such an unstable genus, as opposed to deferring such species descriptions until generic relationships are completely resolved. We would argue that the descriptions of such new species are important since (1) these actions make species names available; (2) they contribute to knowledge of the biodiversity within higher-level clades, and (3) they provide additional published information useful in the future resolution of generic relationships. This new species is herein described as a new Moenkhausia in keeping with the current definition of the genus first proposed by Eigenmann (1903; 1917) and according to the following characters appearing in Géry ’s taxonomic key (1977: 438): “caudal fin scaled, body scales not crenate, predorsal area scaled, maxilla not completely toothed, and lateral line complete”.

Moenkhausia pankilopteryx does not belong in any of the groups proposed by Costa (1994), Weitzman & Palmer (1997), Lima & Toledo-Piza (2001) and Benine (2002), as it is devoid of the features stated by those authors as diagnostic for each of these groups, i.e., the dense reticulate pattern found on body scales; caudal spot preceded by a light area; the complex pigmentation pattern; and visibly perceptible sexual dimorphism, including the larger dorsal fin of males (typical of the “rosy Tetra Clade”) (Weitzman & Palmer, 1997).

It is pertinent to refer here to the proposal of Géry (1977), who split Moenkhausia into three groups on the basis of body depth and number of scales above and below the lateral line, this following an arrangement first introduced by Eigenmann (1917): M. lepidura group , M. grandisquamis group , and M. chrysargyrea group . Géry (1992) later redefined the M. lepidura-group to include those species bearing a black or grey spot on the upper caudal lobe.

Moenkhausia pankilopteryx could be included in the M. chrysargyrea species-group , whose species possess seven or more scales above, and five or more scales below, the lateral line, and with a relatively deep body depth. The new species differs from that group of species, which include M. eigenmanni Gery , M. metae Eigenmann , M. surinamensis Gery , M. miangi Steindachner , M. doceana (Steindachner) , M. jamesi Eigenmann , M. justae Eigenmann , M. pittieri Eigenmann , M. chrysargyrea ( Guenther) , M. comma Eigenmann , and M. naponis Boehlke , by the autapomorphic presence of bony hooks on all fins of mature males and by the combination of the number of branched analfin rays, colour pattern, and body depth.

Other Moenkhausia species belonging to the M. chrysargyrea species-group were described subsequent to Géry (1977): M. margitae Zarske & Gery , from the rio Ucayali drainage in Peru, and M. moisae Gery, Planquette & Le Bail from the rio Maroni and Mana drainages in French Guiana. Moenkhausia pankilopteryx is distinguished from M. margitae by number of branched anal-fin rays (24-27 vs 29-34), humeral spot shape (vertically elongate vs horizontally elongate), and number of lateral-line scales (37-41 vs 34-36); and from M. moisae by number of lateral line scales (37-41 vs 41-47), predorsal scales in a regular series vs irregular series, and presence of bony hooks on all fins of males vs only on the anal-fin rays.

Three Moenkhausia species have previously been described from the rio Tocantins drainage: M. loweae Gery , and M. pyrophthalma Costa , from the rio Araguaia system; and M. tergimacula Lucena & Lucena from upper reaches of the rio Tocantins drainage. Moenkhausia pankilopteryx differs from the aforementioned species by the presence of bony hooks on all fins of males (vs present only on anal-fin rays or absent). Moreover, Moenkhausia pankilopteryx differs from M. loweae by its greater body depth, absence of pigmentation on caudal-fin lobe; from M. pyrophthalma by its greater body depth (43.3- 51.0 vs 28.9-31.6% SL), greater number of lateral-line scales (37-41 vs 27-28), greater number of branched anal-fin rays (24-27 vs 18-19), and colour pattern; and from M. tergimacula by absence of a dark, saddle-like mark anterior to the dorsal-fin origin.

Mature males of M. pankilopteryx possess bony hooks on rays of all fins. Hooks on the fins of Astyanax ojiara were observed and illustrated by Azpelicueta & Garcia (2000). The shape of these bony hooks is similar to those found in M. pankilopteryx (see Description above and Azpelicueta & Garcia, 2000:249-251; figs. 2-7). The presence of hooks on the anal- and pelvic-fin rays, and sometimes also on the caudal-fin rays of males, is commonly found in several genera and subfamilies of Characidae (Azpelicueta & Garcia, 2000; Malabarba & Weitzman, 2003). To date, the presence of bony hooks on all fin rays of mature males has only been reported to M. pankilopteryx and in a few other characids. This feature probably is unique among Moenkhausia species - a putative autapomorphy of M. pankilopteryx , or at least a diagnostic character. The presence of hooks has also been reported to occur on several fins of male specimens of other characid species, namely Hyphessobrycon socolofi Weitzman , H. erythrostigma (Fowler) , and H. hamatus Bertaco & Malabarba (Weitzman, 1977; Bertaco & Malabarba, 2005).

The ichthyofauna of the rio Tocantins drainage is poorly known, with only a few published reports (Merona, 1987; Ferreira, 1993). The rio Tocantins drainage is an area of endemism for several Neotropical freshwater fish groups (Vari, 1988; Menezes & Lucena, 1998; Lima & Moreira, 2003). New characid species have recently been described from this drainage, e. g. Hyphessobrycon hamatus and Astyanax elachylepis Bertaco & Lucinda, 2005 . Especially in its upper regions, the rio Tocantins drainage appears to be a highly endemic center for the Ancistrini, as shown by the presence of three recently described species of Hemiancistrus Bleeker (Cardoso & Lucinda, 2003), and by four endemic species of Ancistrus Kner (Fisch-Muller et al., 2001; 2005).