Acestrocephalus acutus, 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: 397-398

publication ID

http://doi.org/ 10.1590/S1679-62252006000400002

persistent identifier

http://treatment.plazi.org/id/03B55E5E-2678-5A4F-8C0F-F9B44A1BF975

treatment provided by

Carolina

scientific name

Acestrocephalus acutus
status

new species

Acestrocephalus acutus   , new species

Fig.13 View Fig

Holotype. MZUSP 31650 View Materials , mature female, 80 mm SL, Brazil, Pará: Caldeirão, igarapé do Cinzento, rio Itacaiúnas , by Michael Goulding , November , 1983.  

Paratypes. MZUSP 40830 View Materials , 3 View Materials , 73.5 View Materials -101.0 mm SL, Brazil, Tocantins: Arraias, rio Bezerra near bridge on road GO-112, rio Tocantins drainage, by José C. Oliveira, 8 January 1989   ; MZUSP 82105 View Materials , 3 View Materials , 50-68 mm SL, Porto Alegre do Tocantins: rio Manuel Alves da Natividade , rio Tocantins drainage, by Cristiano   R. Moreira, J.C. Nolasco , and M. Ávila, 20 July 2002   , MZUSP 40691 View Materials , 6 View Materials , 51.5-75 mm SL, Goiás: Monte Alegre de Goiás, rio Bezerra , right bank tributary of rio Paraná, rio Tocantins drainage, by José C. Oliveira and Wilson, J.M. Costa, 22 September 1989   ; MCP 15855 View Materials , 1 View Materials , 85 mm SL, Niquelândia : ribeirão da Laje, rio Tocantins drainage, by   R. E. Reis, J. Pezzi, E. Pereira and L.A. Porto, 17 July 1992   ; MNRJ 28716 View Materials , 1 View Materials , 83 mm SL, Niquelândia: rio do Peixe , right bank tributary of rio Maranhão, rio Tocantins drainage, 14º28’S, 48º45’W, by Gustavo Nunan and D.F. Moraes, 08 October 1985 GoogleMaps   ; MNRJ 17612 View Materials , 28 View Materials , 39.4-98 mm SL, Colinas do Sul: pools in rio Tocantins below reservoir of Serra da Mesa , 13º49’S, 48º11’W, by D.F. Moraes, D.A. Halboth, O GoogleMaps   . T. Oyakawa et alii, 1996   ; MNRJ 28717 View Materials , 1, 103.5 mm SL, Minaçu, Cavalcante: rio Tocantins in Serra da Mesa , 14º40’9"S, 52º21’12"W, by P. Buckup, A. Aranda, F. Silva and C. Figueiredo, 29 January 2002 GoogleMaps   ; MNRJ 18315 View Materials , 2 View Materials , 28.5 View Materials and 72.0 mm SL, Colinas do Sul : pools in left bank of rio Tocantins above Ponte Rubião, by D.F. Moraes, D.A. Halboth, O   . T. Oyakawa et al., 28 October 1996   ; MNRJ 21136 View Materials , 1 View Materials , 78 mm SL, Formosa: tributaries of rio Paraná , north of Formosa, 15º28’52"S, 47º20’33"W, by F.A.G. Melo, P.A. Buckup and M GoogleMaps   . R.S. Melo , 21 November 2000   .

Non type material. MZUSP 63009 View Materials , 4 View Materials , 87-96.5 mm SL, Brazil, Mato Grosso: Paranatinga, rio Teles Pires , fazenda do Antônio Bezerra, 14º26’S, 54º36’W, November 1997 GoogleMaps   ; MCP 30 View Materials 485, 2, 76 and 82 mm SL, Nova Canaã do Norte: rio Tels Pires on road between Nova Canaã do Norte and Alta Floresta, 10º14’17"S, 55º48’28"W, 22 January 2002 GoogleMaps   ; MCP 30481 View Materials , 1 View Materials , 39.3 mm SL, Tabaporã: rio Teles Pires on road MT-220 between Sinop and Porto dos Gaúchos, 11º39’15"S, 55º39’18"W, 20 January 2002 GoogleMaps   .

Diagnosis. Among the species of Acestrocephalus   without dark humeral blotch, A. acutus   can be distinguished from A. sardina   and A. nigrifasciatus   by having a smaller eye (28.0- 31.7 vs 32.6-36.5 in A. nigrifasciatus   and 31.3-37.4 in A. sardina   ; compare tables 3, 12 and 13) and an oblong dark blotch at caudal base instead of the triangular dark blotch present on the caudal base of those two species (compare Figs. 3 View Fig , 9 View Fig , and 12). It differs from A. pallidus   by the presence of the oblong dark blotch vs absence of dark blotch at caudal base. The shape of the muscular hiatus of the pseudotympanum and the muscular arrangement around it in A. acutus   and A. pallidus   are also different (compare figs. 5f and 5g). Acestrocephalus acutus   differs from A. anomalus   by having more teeth in the posterior row on dentary (28-36 vs 23-28) and fewer teeth in the external tooth row on premaxilla (6-8 vs 8-11).

Description. Morphometrics of holotype and additional specimens presented in Table 13. Meristic and morphometric data based on all lots in type series. No statistical differences found among population samples studied. Body relatively large (SL= 50-103.5 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=47, including holotype. Posterior most ray unbranched, n=47. Adipose fin present. Anal-fin rays iv,31 (iv or v, usually iv unbranched, branched rays mean=32, range 29-35, n=47, posterior ray split to its base and counted as 1). Modestly developed anterior anal-fin lobe including anterior unbranched rays and first 8-9 branched rays. Three sexually mature males with bilateral hooks on posterior anterior branched rays. One sexually mature male ( MCP 15855 View Materials , 85 mm SL) has hooks on first 14 branched anal-fin rays, number of hooks per ray increasing from first (5) to sixth (14) then decreasing from seventh (12) through tenth (5), 13th (3) and 14th (1). Pectoral-fin rays i,12 (anterior unbranched ray i, n=47, branched rays mean 12.7, range 11-14, n=47). Posterior tips of longest pectoral-fin rays reaching to about one third of pelvic-fin length. Pelvic-fin rays i,7, n=47. No pelvic-fin ray hooks on sexually mature males. Distal tips of longest pelvic-fin rays reaching anterior border of anus. Principal caudal-fin ray count 10/9, n=47.

Lateral line complete, perforated scales 74 (mean=73.8, range 70-77, n=46). Scale rows above lateral line 13 (mean=12.9, range 12-14, n=46). Scale rows below lateral line 11 (mean=11.4, range 10-14, n = 46). Scale rows around caudal peduncle 23 (mean=22.8, range 22-24, n=46).

Shape, size and arrangement of teeth on premaxilla, maxilla and dentary as in A. sardina   . Outer row small conical teeth on premaxilla 9 (mean=8.3, range 7-10, n=47). Maxillary teeth 36 (mean=33.6, range 28-38, n=47). Fig. 6 View Fig suggests a tendency for the number of maxillary teeth to increase in number according to an increase in standard length. Posterior row dentary teeth 33 (mean=30.5, range 28-36, n=47), tending to increase in number with an increase in standard length ( Fig.7). Inner row dentary teeth 11 (mean=11.2, range 10-13, n=47).

Vertebrae 38 (mean=38.7, range 37-39, n=28). Total number of gill-rakers on first gill-arch 7 (mean=6.6, range 6-8, n= 47).

Branchiostegal rays 4; 3 originating on anterior and one on posterior ceratohyal.

Muscular hiatus of pseudotympanum reduced, constricted by dorsal and ventral fibers of obliquus superioris muscle ( Fig. 5f View Fig ). Cavity anterior to first pleural rib, this as well as obliquus inferioris muscle not visible. Second pleural rib partially exposed.

Color in alcohol. Body pale yellow slightly darker dorsally due to presence of dark chromatophores along free edge of scales, lighter ventrally. Dorsal part of head and snout more densely pigmented with dark chromatophores. Lateral head and opercular bones with scattered dark chromatophores. Anterior upper edge of lower jaw also heavily pigmented with dark chromatophores. Dark lateral body stripe extending from

Characters Holotype N Range Mean SD Standard length 80.0 47 50.0-103.5

Body depth 26.6 41 23.5-28.6 25.3 1.1 Snout to dorsal-fin origin 48.7 47 48.7-54.2 51.4 1.0 Snout to pectoral-fin origin 30.7 47 27.6-31.5 29.7 0.9 Snout to pelvic-fin origin 43.2 47 41.0-45.4 42.5 1.1 Snout to anal-fin origin 59.0 47 56.1-61.4 58.0 1.3 Caudal peduncle depth 8.1 47 7.5-8.8 8.1 0.3 Caudal peduncle length 8.7 47 8.1-11.0 9.4 0.5 Pectoral-fin length 17.7 47 14.7-18.3 16.4 0.7 Pelvic-fin length 15.0 47 12.6-15.5 13.7 0.8 Dorsal-fin base length 11.2 47 11.0-12.8 11.7 0.4 Dorsal-fin height 25.3 47 21.2-26.6 24.2 1.1 Anal-fin base length 35.6 47 32.7-37.6 35.4 1.0 Anal-fin height 17.5 47 14.0-18.6 15.7 1.3 Eye to dorsal-fin origin 34.1 47 34.1-37.8 36.2 1.0 Dorsal-fin origin to caudal-fin base 51.5 47 48.6-53.2 51.0 1.0 Head length 29.7 47 29.0-33.3 30.4 0.8 Horizontal eye diameter 31.1 47 28.0-31.7 29.4 0.8 Snout length 30.2 47 27.1-30.4 28.6 0.7 Least interorbital distance 18.0 47 16.0-19.7 17.6 0.7

behind upper opercle to caudal peduncle, wider from below dorsal-fin origin to origin of adipose fin, narrower from below dorsal-fin origin anteriorly and on caudal peduncle. Oblong dark blotch on anterior caudal base joining dark lateral stripe, extending posteriorly to bases of middle caudal-fin rays. Mental area of lower jaw with conspicuous dark blotch in some specimens. Black spot at origin of dorsal fin very conspicuous, anteriorly extending over two or three predorsal scales, laterally over three or four scales of first horizontal scale row. All fins pale, first unbranched dorsal and pectoral fin rays with scattered dark chromatophores.

Distribution. Acestrocephalus acutus   is known from the rio Tocantins and rio Tapajós drainages. It is sympatric with A. maculosus   and A. stigmatus   in the upper rio Tocantins ( Fig. 8 View Fig ).

Remarks. The specimens from rio Teles Pires in the rio Tapajós drainage, not included as type material, are morphologically undistiguinshable from the holotype and paratypes, but examination of more specimens is required for better comparison.

Etymology. The species name acutus   , adjective, from Latin meaning sharp is in reference to the pointed nature of the snout of this species.

R

Departamento de Geologia, Universidad de Chile

MCP

Pontificia Universidade Catolica do Rio Grande do Sul

T

Tavera, Department of Geology and Geophysics