Microglanis oliveirai, Ruiz & Shibatta, 2011

Ruiz, William Benedito Gotto & Shibatta, Oscar Akio, 2011, Two new species of Microglanis (Siluriformes: Pseudopimelodidae) from the upper-middle rio Araguaia basin, Central Brazil, Neotropical Ichthyology 9 (4), pp. 697-707 : 698-701

publication ID

https://doi.org/ 10.1590/S1679-62252011000400002

persistent identifier


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scientific name

Microglanis oliveirai

new species

Microglanis oliveirai , new species

Fig. 1 View Fig

Holotype. INPA 35623 View Materials , 26.3 mm SL, Brazil, Mato Grosso, Barra do Garças, Vale dos Sonhos District, BR-158 road, km 750, rio Corrente (right margin tributary of the rio das Mortes), rio Araguaia basin, 15°29’56.3”S 52°12’10.8”W, 31 Jul 2008, W. B. G. Ruiz, L. R. Jarduli & E. S. Silva. GoogleMaps

Paratypes. All from Brazil, Mato Grosso State, rio Araguaia basin : MZUEL 5175 , 11 , 19.6-25.4 mm SL (2 c&s, 21.7-23.3 mm SL), same data as holotype GoogleMaps . LBP 1852 , 4 , 21.0- 22.2 mm SL, Barra do Garças, rio Insula (tributary of rio das Mortes ), 15°32’54.2”S 52°12’17.7”W, 27 Aug 2003, C. Martin GoogleMaps . MZUSP 86239 View Materials , 3 View Materials , 18.6 View Materials - 21.0 mm SL, Cocalinho, rio Cristalino, 47 km from Cocalinho , MT 326 road, 14°12’45”S 51°18’21”W, 14 Oct 2004, AXE Expedition [O. T. Oyakawa et al.] GoogleMaps . MZUSP 86222 View Materials , 10 View Materials , 17.7-24.5 mm SL, Cocalinho, rio Corixo da Saudade ( Corixinho ) (tributary of rio Cristalino ), 25 km North of Cocalinho, MT 326 road, 14°17’20.6”S 51°9’12.1”W, 13 Oct 2004, AXE Expedition [O. T. Oyakawa et al.] GoogleMaps . MZUSP 86260 View Materials , 2 View Materials , 20.5-21.22 mm SL, Cocalinho, corixão do Meio (tributary of rio Cristalino ), 42 km North of Cocalinho, MT- 326 road, 14°11’14”S 51°14’58”W, 14 Oct 2004, AXE Expedition [O. T. Oyakawa et al.] GoogleMaps . MZUSP 86253 View Materials , 2 View Materials , 17.6-22.1 mm SL, Cocalinho, ribeirão Água Preta (tributary of rio Cristalino ), 79 km North of Cocalinho, MT 326 road, 14°08’57”S 51°32’21”W, 14 Oct 2004, AXE Expedition [O. T. Oyakawa et al.] GoogleMaps .

Diagnosis. Microglanis oliveirai is readily distinguished from all congeners in the possession of the following characters: short lateral line, reaching only the vertical line through base of dorsal-fin spine; 3-6 lateral line pores; 3-6 gill rakers in the first branchial arch; 10-11 branched caudal fin rays; 5 pleural ribs; 27-28 free vertebrae; large anterior fontanel; small supraoccipital process not contacting anterior nuchal plate; small nuchal shield.

Description. Small size; largest examined specimen 26.3 mm SL. Morphometric data presented in Table 1. Body elongate, depressed anteriorly, especially at head, compressed posteriorly from pectoral-fin insertion. Greatest body depth at dorsal-fin origin, approximately elliptical in cross section. Greatest body width at pectoral girdle. Dorsal profile slightly convex on predorsal region, almost straight or slightly concave from dorsal-fin spine to anterior region of adipose fin, and concave at caudal peduncle. Ventral profile slightly convex from mouth to pectoral-fin base, approximately straight from later point to anal-fin and concave from anal fin origin to ventral procurrent caudal-fin rays. Head as wide as long, strongly depressed, anteriorly rounded in dorsal view. Small eyes, situated dorsolaterally, covered by skin, without free orbital margin and positioned at midlength of HL. Snout short. Anterior nostril tubular, close to upper lip; posterior nostril larger, rounded, close to eye, with small flap on anterior portion. Mouth gape wide. Barbels thin, short, slightly flattened in cross section. Maxillary barbel surpassing base of pectoral-fin spine. Mental barbels arranged in arc along ventral surface of jaw; outer pair surpassing base of pectoral-fin spines; inner pair shorter, slightly less than one-half length of outer mental barbels.

Pectoral fin roughly triangular in dorsal and ventral views, rays I,5. Pectoral-fin spine long, strong, flat, recurved at midpoint, strongly serrated in both margins, covered by thin skin. Anterior margin of pectoral-fin spine with four to eight retrorse serrations proximally, followed by none to two Yshaped serrations, and two to seven antrorse serrations distally (total = 9-13[32]). Posterior margin with six to 10[32] retrorse serrations, larger than those of anterior margin. Tip of pectoral-fin spine strongly ossified ( Fig. 2 View Fig ). Pectoral fin not reaching pelvic-fin base. Dorsal fin II,6 (spinelet present); rounded margin, slightly deeper than long. Dorsal-fin spine straight, smooth, shorter than soft rays and covered by skin. Dorsal fin not reaching adipose-fin base when adpressed. Pelvic fin i,5, roughly semicircular in ventral view, its origin situated at midbody close to vertical line through two last dorsal-fin rays, when adpressed not reaching anal-fin base. Adipose fin relatively small, with rounded posterior margin free.Anal fin relatively large and deep, with rounded margin, 10[15] or 11*[17] total rays. Anal-fin base slightly smaller than adipose-fin base. Longest anal-fin rays reaching first ventral procurrent caudal-fin rays. Caudal fin large, deep, slightly forked; rounded lobes, with upper lobe well developed; 10[20] or 11*[12] branched rays, 15 dorsal procurrent rays, nine to 10 smaller ventral procurrent rays. Caudal peduncle relatively long (15.5-17.6 % SL).

Lateral line incomplete, not reaching the vertical through the first branched dorsal-fin ray; 3[1], 4[7], 5*[16], or 6[8] large pores, about half diameter of parieto-supraoccipital fontanel. Cephalic sensory canals with eight pores on mandibular canal; one on preopercle canal; four on infraorbital canal; one on antorbital branch of infraorbital canal; five on supraorbital canal; one on parietal branch of supraorbital canal; one on otic canal; and two on postotic canal. Parietal branch of supraorbital canal with one terminal pore. Cephalic neuromasts lines with three or four small neuromasts on nasal line, one on rostral line, four to six on mandibular line, two on anterior line, and two on supratemporal accessory line. Trunk neuromasts lines with two neuromasts on dorsal-trunk line, six to 12 on medium trunk line, five to eight on subdorsal-trunk line, and five to seven very small neuromasts on subventral-trunk line.

Premaxillary tooth patch narrow, long, weakly curved, lateral margin slightly rounded, without posterior projections, with notch at symphysis. Dentary tooth patch slightly narrower than, and about twice the length of, the premaxillary tooth patch, with notch on mandibular symphysis. Teeth small, villiform, pointing posteriorly, teeth larger on dentary patch. Gill rakers spiny, unbranched, and relatively small. First branchial arch bearing few rakers: 0+1+2=3[4], 0+1+3=4*[6], 1+1+1=3[5], 1+1+2=4[9], 1+1+3=5[5], or 1+1+4=6[2]. Branchiostegal membranes free from isthmus. Branchiostegal rays 9-10. Free vertebrae 27-28. Pleural ribs 5. Anal-fin proximal pterygiophores 9-10. Gas bladder large, cordiform, with simple inner T-shaped septum.

Color in alcohol. Ground color light brown. Ventral region of body and head pale with brown spots. Head dark brown, with lateral portions of head, margin of opercle, anterior and posterior nostrils, and pores of cephalic canals light colored. Wide, irregular light band passing through nape and anterior portion of trunk, immediately after opercular opening. Upper lip dark, lower lip light. Light barbels speckled with dark brown spots. Overall trunk color light brown, with faint vermiculated stripes. Three large dark brown blotches, appearing dorsally as saddle markings. First blotch similar to an inverted U, below dorsal fin, reaching horizontal line through axis of trunk. Second blotch more elongated, situated immediately below adipose fin, extending posteroventrally to reach the brown blotch at anal-fin base. In some specimens, this sub-adipose blotch is divided in two by a light band across the horizontal axis of the body. Third blotch positioned at middle to posterior portions of caudal peduncle, roughly triangular-shaped, with one of vertices pointing anteriorly. Middle trunk-line neuromasts faintly surrounded by melanophores. Pectoral and pelvic fins hyaline, slightly speckled with brown pigmentation over rays. Medial to distal portion of pectoralfin spine with a large dark brown blotch. Dorsal fin mostly hyaline, a large dark blotch situated at anterior basal portion of fin, extending into dorsal-fin spine.A brown, narrow stripe running midway between dorsal-fin base and margin. Adipose fin with one oval light blotch on anterior portion, followed by narrow brown stripe, and light area slightly speckled with melanophores. Anal fin mostly hyaline, speckled with melanophores, concentrated as a small, relatively diffuse anterior basal portion and, in large specimens, a weak, brown arched stripe, on middle portion of anal fin between the 3 rd and 6 th rays. Caudal fin hyaline, speckled with brown cromatophores, with one straight, vertical dark brown stripe on the base. In larger specimens a narrow stripe shaped approximately like the numeral three, located at the middle of the fin.

Distribution. Microglanis oliveirai is known from tributaries of rio das Mortes and rio Cristalino ( Fig. 3A View Fig ), upper-middle rio Araguaia basin, State of Mato Grosso, Brazil ( Fig. 4 View Fig ).

of rio Claro , between Aragarças and Jussara, 15° 52’ 10.9”S 51° 32’ 56.7”W, V. A. Bertaco, F. R. Carvalho & F. C. Jerep GoogleMaps .

Diagnosis. Microglanis xylographicus is easily distinguished from its congeners by two characters related to color pattern: (1) trunk brown with horizontal light stripes that in conjunction impart a tree-bark pattern, and (2) absence of any light marks (blotch or transversal band) crossing the occipital region. The new species can be further distinguished from its congeners, except Microglanis robustus , by the neuromasts surrounded by melanophores, forming three series of aligned small black points laterally on the trunk, four series in the head, one series on the lateral of nape, and one series posterior to the nape. It is distinguished from M. robustus by having a relatively long snout 11.4-12.9% SL (vs. 9.1-10.7% SL), and five pleural ribs (vs. 6 or 7).

Description. Small size, largest examined specimen 27.8 mm SL. Morphometric data presented in Table 1. Dorsal profile convex on predorsal region, almost straight from dorsal-fin origin to anterior region of adipose fin, and concave from latter point to anteriormost procurrent caudal-fin ray. Ventral profile gently convex from lower lip to pelvic-fin origin, slightly concave from latter point to anal-fin origin, slightly convex at origin of analfin, and concave from latter point to anteriormost ventral Etymology. Microglanis oliveirai is named in honor of Claudio de Oliveira, from the Universidade Estadual Paulista “Júlio de Mesquita Filho”, campus Botucatu (SP), in recognition of his extensive contribution to the knowledge of Neotropical fish evolution.

Remarks. Specimens collected at the rio Cristalino basin have larger interorbital width and possess an overall darker coloration when compared with specimens of the rio das Mortes basin.