Microglanis xylographicus, 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 : 701-704

Microglanis xylographicus , new species Fig. 5

Holotype. INPA 35624 , 27.8 mm SL, Brazil, Goiás State, Aragarças, córrego Jaraguá (tributary of rio Araguaia ), road to Torixoréu , 15°56’26.9”S 52°15’18.2”W, 31 Jul 2008, W. B. G. Ruiz, L. R. Jarduli & E. S. Silva.

Paratypes. All from Brazil, rio Araguaia basin. Goiás State. MZUEL 5174 , 2 , 23.1-26.2 mm SL, same data as holotype. Mato Grosso. MZUEL 5173 , 4 , 18.2-22.3 mm SL (1 c&s, 21.5 mm SL), rio Corrente (tributary of rio das Mortes), BR-158 road, km 750, Vale dos Sonhos, 15°29’56.29”S 52°12’10.75”W, 31 Jul 2008, W. B. G. Ruiz, L. R. Jarduli & E. S. Silva. LBP 11521, 10 , 16.9-23.7 mm SL (1 c&s, not measured), 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. LBP 1684 , 23.8 mm SL, rio das Garças, 15°54’18.1”S 52°19’24.2”W, 13 Jul 2002, C. Oliveira. Goiás. LBP 1852 , 2 , 18.7-20.9 mm SL, rio Insula , Barra do Garças , 15 o 32’54.2”S 52 o 12’17.7”W, 27 Aug 2003, C. Martin. UFRGS 13166 , 1 , 21.7 mm SL, Aragarças, stream tributary procurrent caudal-fin ray. Body depressed in the region anterior to dorsal-fin origin, becoming gradually compressed posteriorly from pectoral-fin. Greatest body depth at dorsal-fin origin; body roughly triangular in cross section. Greatest body width at pectoral girdle. Head broad, depressed and slightly rounded in dorsal view. Small eyes, positioned dorsolaterally, covered by skin, without free orbital margin, closer to mouth than to opercular opening. Anterior nostril tubular, close to upper lip, situated just anterior to vertical line through base of maxillary barbel. Posterior nostril rounded, close to orbital margin, with conspicuous flap on anterior portion. Mouth wide, its gape occupying almost entire width of head. Barbels short, thin, flattened in cross section. Maxillary barbel reaching pectoralfin spine base in some specimens. Two mental pairs, outer pair reaching, or falling short of, pectoral-spine base, inner pair about one-half length of outer mental barbel .

Pectoral fin roughly triangular in dorsal and ventral view, I,5, when adpressed not reaching pelvic-fin base. Pectoral-fin spine strong, flattened, slightly arched, completely covered by thick skin, with large serrations on both sides. Anterior margin of pectoral-fin spine with seven to 11 retrorse serrations proximally, followed by none to two slightly forked or rarely Y-shaped serrations, and none to four small antrorse serrations (total = 9-14[18]). Posterior margin of pectoral-fin spine with five to eight [18] retrorse serrations, larger than those of anterior margin. Tip of pectoral-fin spine ossified and pointed ( Fig. 6 ). Dorsal fin II,6 (spinelet present), inserted almost at anterior midbody, deeper than longer, margin slightly rounded, when adpressed usually reaching adipose-fin base. Dorsal-fin spine straight, smooth, covered by skin, about the same length of last branched ray. Pelvic fin i,5, its insertion situated at midbody, margin rounded, and when adpressed, not reaching anal-fin base. Adipose fin moderately long and deep, with posterior margin free and angular, not confluent with caudal fin, and located above anal-fin origin. Anal fin large and deep, with 10[9], 11*[8], or 12[1] rays, and rounded margin. Anal-fin base shorter than adipose-fin base. Posterior anal-fin rays reaching first two ventral procurrent caudal-fin rays. Caudal fin large, deep, bilobed; upper lobe usually longer than lower lobe, with 12*[15] or 13[3] branched rays, 16 dorsal procurrent rays, and 10 smaller ventral procurrent rays. Caudal peduncle deep (12.3-14.4% SL) and long (16.8-18.5% SL).

Lateral line incomplete, but usually reaching or surpassing vertical line through posterior portion of dorsalfin base; 7[3], 8[6], 9[5], 10*[2], 11[1], or 12[1] small pores. 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. Pterotic branch deprived of pores. Cephalic neuromasts lines with four or five small neuromasts on nasal line, one on rostral line, five to seven 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 13 on medium trunk line, five to eight on subdorsal-trunk line, and four to eight small neuromasts on subventral-trunk line.

Premaxillary tooth patch narrow, long, slightly curved, rounded lateral margin, without posterior projections, and with large notch at symphysis. Dentary tooth patch semicircular, narrow, of similar width of premaxillary tooth patch, but more than double its length, with notch on symphysis. Teeth small and villiform, pointing posteriorly. Gill rakers spiny and unbranched. Gill rakers on first branchial arch: 1+1+3=5[1], 1+1+4=6[13], 1+1+5=7[1], 2+1+3=6[2], or 2+1+5=8*[1]. Opercular membranes free from isthmus, supported by 8 or 9 branchiostegal rays. Free vertebrae 28. Pleural ribs 5. Anal-fin proximal pterygiophores 9. Gas bladder large, cordiform, with simple inner T-shaped septum.

Color in alcohol. Body almost entirely brown; anterior region darker; lateral portions of trunk and caudal peduncle with light brown horizontal streaks, imparting a pattern similar to tree bark, more concentrated on dorsal and median regions of body. Dorsal region of body completely dark brown, ventral region slightly mottled with brown spots. Head dark brown, with one lateral black stripe that extends to a region anterior to nostrils, uniting eye to upper lip. Upper lip dark, lower lip light. Barbels (mainly maxillaries) slightly mottled with brown. Melanophores surrounding neuromasts of all superficial lines, forming small, conspicuous black dots distributed in three horizontal rows along lateral portion of body, two dots above opercular opening, four dots on posterior top of head, and four dots on predorsal region. Caudal peduncle with a weak brown blotch of irregular shape. Pectoral, pelvic, anal and caudal fins hyaline, with speckled brown pigmentation roughly arranged in rows along fin rays. Dorsal fin with two conspicuous horizontal dark brown stripes, the first basal and wide, the second a little above dorsal-fin middle half, absent in small specimens. Dorsal-fin spine dark brown, pectoral-fin spine light brown, with dark brown speckles. Anterior portion of adipose fin light, followed by a dark brown blotch, central and posterior portions light-colored, with small irregular light brown blotches. Anal fin mostly hyaline, with dark speckling and with small brown blotches on anterior margin, absent in small specimens. Caudal fin hyaline, speckled with light brown pigmentation forming weak, vertical light brown stripes over fin rays; a wide, conspicuous, straight vertical stripe at caudal-fin base, and a second, considerably less conspicuous vertical stripe, situated slightly after caudalfin middle half, roughly shaped like the numeral three, present only in large specimens.

Distribution. Microglanis xylographicus is known from tributaries of the rio das Mortes and small nearby direct tributaries of the rio Araguaia such as the córrego Jaraguá ( Fig. 3B ) and rio das Garças, in States of Mato Grosso and Goiás, Brazil ( Fig. 4 ).

Etymology. The name xylographicus is derived from the Greek xylos referring to wood, and graphikos, of writing. It is a reference to the horizontally striated color pattern, like a tree bark. An adjective.

Remarks. Specimens from the type locality, the córrego Jaraguá, are larger than specimens collected at the rio Insula and rio Corrente (23.1-27.8 vs. 16.9-23.8 mm SL), have more neuromasts on median-trunk line (11-13 vs. 6-11), larger mouth width (48.0-49.7% vs. 44.2-47.1% HL), smaller orbital diameter (3.4-3.8% vs. 3.7-4.4% SL), smaller dorsal-fin spine length (11.8- 13.1% vs. 12.9-16.2% SL), larger posterior cleithral process length (11.7-12.2% vs. 9.2-11.6% SL), smaller adipose-fin base length (17.8-19.8% vs. 19.5-21.1% SL), and a darker brown color. The two populations are separated (about 90 km) by the Serra do Roncador and Serra Azul, indicating that those differences might be geographically related. In the absence of additional evidence, we consider that the two populations belong to a single species.

Figures

Fig. 5. Microglanis xylographicus, holotype, INPA 35624, 27.8 mm SL, córrego Jaraguá, rioAraguaia basin, Goiás State, Brazil. Dorsal, lateral and ventral views.

Fig. 6. Left pectoral-fin spine in dorsal view of paratype of Microglanis xylographicus, MZUEL 5174, 26.2 mm SL. Scale bar = 1 mm.

Fig. 3. (A) rio Cristalino, rio Araguaia basin, Mato Grosso State (photo by José Birindelli), (B) córrego Jaraguá, rio Araguaia basin, Goiás State, and (C) rio Corrente, rio das Mortes basin, Mato Grosso State.

Fig. 4. Map of South America showing the distribution of species of Microglanis, with the exception of M. ater, whose type locality was originally cited as “Mittelbrazil”. Microglanis carlae (open inverted triangle), M. cibelae (open circle), M. cottoides (open square), M. eurystoma (open diamond), M. garavelloi (solid horizontal rectangle), M. iheringi (open triangle), M. leptostriatus (solid vertical rectangle), M. malabarbai (solid triangle), Microglanis minutus (clover), M. nigripinnis (cross), M. oliveirai (spiny dot), M. parahybae (X), M. pataxo (solid square inside open square), M. pellopterygius (solid inverted triangle), M. poecilus (solid square), M. robustus (solid circle), M. secundus (solid diamond), M. variegatus (asterisk), M. xylographicus (star), and M. zonatus (solid circle inside solid square). Upper rio Araguaia basin area in inset: 1, rio Araguaia; 2, rio das Garças; 3, rio das Mortes; 4, rio Corrente; 5, rio Cristalino. Gray point indicates the city of Barra do Garças, Mato Grosso State. Star with white point indicates the type-locality of Microglanis xylographicus. Spiny dot with white point indicates the type-locality of Microglanis oliveirai.