Acestrocephalus maculosus, Menezes, 2006

Menezes, Naércio A., 2006, Description of five new species of Acestrocephalus Eigenmann and redescription of A. sardina and A. boehlkei (Characiformes: Characidae), Neotropical Ichthyology 4 (4), pp. 385-400 : 393-394

Acestrocephalus maculosus , new species Fig.10

Holotype. MZUSP 53974 , 79 mm SL, immature female, Brazil, Goiás: Minaçu, córrego Água Parada, tributary of rio do Peixe , Serra da Mesa , Miguel T. Rodrigues et al., May 1996.

Paratypes. MZUSP 90162 , 1 , 72 mm SL, taken with holotype . MNRJ 12714 , 1 , 42.3 mm SL, Brazil, Goiás: Uruaçu, rio Palmeira , left bank tributary of rio Maranhão, upper rio Tocantins basin, G.W. Nunan and D.F. Moraes Jr., 17 October 1985 ; MNRJ 12657 , 3 , 44-62 mm SL, Niquelândia: rio do Peixe, right bank tributary of rio Maranhão, upper Tocantins basin, G.W. Nunan & D.F. Moraes Jr, 08 October 1985 .

Diagnosis. Acestrocephalus maculosus has a dark blotch at the humeral region, a character shared only with A. boehlkei and A. stigmatus . In the diagnosis of A. boehlkei the differences among these species are discussed. Acestrocephalus maculosus can be easily distinguished from A. stigmatus by the number of anal-fin rays (25-27 vs 29-31), and total number of gill-rakers (7-8 vs 5-6). See Tables 4 and 9. The general structure of the pseudotympanum of A. maculosus ( Fig. 5c ) is quite peculiar and different from that of A. stigmatus ( Fig. 5d ) and all the other species of Acestrocephalus examined ( Figs. 5a, b, e, f and g ). In A. maculosus the muscular hiatus is very reduced as the result of the great development of the obliquus superioris muscle covering the anterior portion of the swim bladder. As a consequence, the opening anterior to first pleural rib, this and the second pleural rib as well as the obliquus inferioris muscle are not visible.

Description. Morphometrics of holotype and paratypes presented in table 10. Body relatively small (SL= 42.3-79 mm). Body form, dorsal and ventral body profiles, shape of snout and mouth and extension of maxilla as in A. sardina .

Dorsal-fin rays ii, 9 in all specimens, n=6, including holotype. Posterior most ray unbranched, n=6. Adipose fin present. Anal-fin rays iv,27 (iv or v, usually iv unbranched, branched rays mean=26.5, range 25-27, n=6, posterior ray split to its base and counted as 1). Moderately developed anterior anal-fin lobe including anterior unbranched rays and first 6-7 branched rays. No hooks on anterior rays of two sexually mature males (MZUSP 90162, 92 mm SL and MNRJ 12657, 62 mm SL). Pectoral-fin rays i,14 (anterior branched ray i, n=6) branched rays mean=14, range 13-15, n=6. Posterior tips of longest pectoral-fin rays reaching scarcely beyond pelvic-fin origin. Pelvic-fin rays i,7, n=6. No hooks on pelvic–fin rays of sexually mature males. Distal tips of longest pelvic-fin rays extending slightly beyond posterior border of anus, falling short of origin of anal fin. Principal caudal-fin ray count 10/9, n=6.

Lateral line complete, perforated scales 73 (mean=72.5, range 71-73, n=6. Scale rows above lateral line 14, n=6. Scale rows below lateral line 12, n=6. Scale rows around caudal peduncle 23, n=6.

Shape, size and arrangement of premaxillary, maxillary and dentary teeth as in A. sardina . Outer row small conical teeth on premaxilla 9 (mean=8.5, range 7-9, n=6). Maxillary teeth 35 (mean=37, range 35-40, n=6), possibly increasing in number with an increase in standard length although no clear evidence detected from data taken from type series. Posterior dentary teeth 24 (mean=25.5, range 35-40, n=6), also probably increasing in number ontogenetically. Inner row dentary teeth 12 (mean=12.8, range 12-14, n=6).

Vertebrae 41 (mean 40.2, range 39-41, n=6). Total number of gill-rakers on first gill-arch 7 (mean=7.5, range 7-8, n=6).

Obliquus superioris muscle greatly developed, reducing muscular hiatus of pseudotympanum to small slit and completely covering cavity anterior to first pleural rib, this, second pleural rib and obliquus inferioris muscle ( Fig. 5c ).

Color in alcohol. Body color light brown to pale yellow, head and trunk profusely covered with dark chromatophores. Chromatophores on head mostly concentrated dorsally, as well as snout, anterior border of lower jaw, maxilla, circumorbital bones and opercle. Dark chromatophores especially abundant along free edge of scales in both dorsal and anterior ventral parts of trunk. Dark irregularly shaped blotch at humeral region, slightly longer than deep. Dark lateral stripe extending from posterior part of humeral dark blotch to caudal peduncle joining oblong dark blotch at caudal-fin base, dark color extending to bases of middle caudal-fin rays. Lateral body stripe wider from dorsal-fin origin to adipose-fin origin, narrower from dorsal-fin origin anteriorly to humeral blotch and on caudal peduncle. Mental area of lower jaw with diffuse dark blotch. Dorsal-fin origin with black spot extending to base of first unbranched dorsal-fin ray. Fins pale with scattered dark chromatophores more abundant on dorsal and caudal fins.

Distribution. Acestrocephalus maculosus is known only from tributaries of the upper Tocantins ( Fig. 8 ).

Etymology. The species name maculosus , adjective, comes from Latin meaning spotted. It is in reference to the dark spots and stripes on the body of this species.

Figures

Fig. 10. Acestrocephalus maculosus, MZUSP 53974, holotype, 79 mm SL, immature female, córrego Água Parada, rio Tocantins drainage.

Fig. 5. Schematic drawings of external view of muscles covering the anterior portion of the swim bladder inA – Acestrocephalus sardina (MZUSP 29241); B – A. boehlkei (MZUSP 38699); C – A.maculosus (MNRJ 12657); D – A. stigmatus (MZUSP 10422); E – A. nigrifasciatus (MCP 30420); F – A. acutus (MNRJ 17612); G – A. pallidus (MZUSP 73471).Anterior towards left; 1 plr (first pleural rib); 2 plr (second pleural rib); os (obliquus superioris); ls (lateralis superficialis); oi (obliquus inferioris). Not drawn to scale.

Fig. 8. Map of northern and central South America showing the geographic distribution of the species of Acestrocephalus. Some symbols may represent more than one locality.