Microglanis leptostriatus, Horácio Mori & Oscar Akio Shibatta, 2006

Horácio Mori & Oscar Akio Shibatta, 2006, A new species of Microglanis Eigenmann, 1912 (Siluriformes, Pseudopimelodidae) from rio São Francisco basin, Brazil., Zootaxa 1302, pp. 31-42 : 33-40

Microglanis leptostriatus , new species

Fig. 1

Holotype. MZUSP 85985 (42.3 mm SL), rio Verde Grande , 16º 39´S / 46º11´57,8”W, Montes Claros , State of Minas Gerais, Brazil, 31.viii.2004, A. Akama et al.

Paratypes. Brazil. Minas Gerais: MCP 16647 (10 specimens, 18.88-30.45 mm SL), rio Carinhanha , 16.vii.1993, R. E. Reis et al. ; ANSP 172127 (10 specimens), Rio da Cruz on road from Januaria to Fabiao , 15°20'44"S, 44°14'02"W, W. Saul et al., 14.vii.1993 ; MZUEL 3733 (6 specimens, 19.29-27.33 mm SL), from the same locality and collectors as ANSP 172127 ; MZUSP 47408 (5 specimens, 17.90-24.39 mm SL), rio Serra Branca, Porteirinha , 23.vii.1994, MZUSP/USNM/UFSCar Expedition ; MZUSP 47456 (2 specimens, 28.33-28.35 mm SL), Montes Claros, rio Verde , 23.vii.1994, MZUSP/USNM/ UFSCar Expedition, ; MZUSP 86144 (11 specimens, 24.74-36.63 mm SL), collected with the holotype.

Diagnosis. The following combination of characters differs Microglanis leptostriatus from its congeners: light transverse stripe, located in occipital region between the opercular openings, thin and sinuous, sometimes discontinuous; pale region below dorsal and adipose fins mottled with brown spots; dark stripe in the axis of gill filaments in alcohol preserved specimens (figure 2). Microglanis leptostriatus is further distinguished from M. parahybae (table 1) and M. garavelloi , the closest species geographically, by having the following combination of characters: longer head length [28.3-32.1% of SL (mean = 30.0) versus 25.5-28.5% (mean = 27.2) and 25.2-30.2 (mean = 28.0), respectively], shorter dorsal spine length [11.7-14.9% of SL (mean = 13.6) versus 14.1-18.1% (mean = 16.0) and 11.3-19.0 (mean = 15.5)], shorter pectoral spine length [12.5-19.7% of SL (mean = 17.4) versus 19.4-22.7% (mean = 20.6) and 18.5-26.2 (mean = 22.1)].

Description. Morphometric data summarized in Table 1. Head and anterior portion of body depressed, becoming laterally compressed from pectoral girdle towards caudal region. Greatest body depth at dorsal fin origin, greatest body width at pectoral fin base. Anterior dorsal profile of body straight or gently convex, ventral profile gently convex. Head broader than long, rounded in dorsal view. Eyes small, superior, orbital rim not free, covered by skin. Snout short, anterior nostril tubular, close to upper lip; posterior nostril with raised flap close to eye. Mouth wide and terminal. Premaxillary tooth patch rounded, without backward projecting angles; teeth small and villiform. Dentary tooth patch semicircular, longer than premaxillary tooth patch. Barbels thin, flattened in cross section. One maxillary and two mental pairs of barbels. Maxillary barbel longest, reaching base of pectoral spine. Lateral line incomplete, with 7* (6), 8(10), 9 (10), 10 (2), 11 (1) pores, reaching vertical line through posterior base of dorsal fin. Lateral line followed by isolated neuromasts as far posteriorly as vertical line through middle of adipose-fin. Gill membranes free. Gill rakers filiform; gill rakers on first arch 1,1,4 (4), 1,1,5 (7), 1,1,6 (1), 2,1,4 (3), 2,1,5 (5), 2,1,6 (6), 2,1,7* (3). Dorsal fin rounded, positioned anterior of middle of standard length, with one spinelet and I+6 rays. Anterior and posterior margins of dorsal spine smooth. Dorsal spine short, smaller than soft rays. Elongated adipose fin with free posterior margin. Caudal-fin emarginate, with upper lobe a little more developed than lower, both lobes with rounded tips; principal caudal rays, 12 (4), 13* (23), 14 (1). Pectoral-fin triangular. Tip of adpressed pectoral fin does not reach base of pelvic fin. Pectoral fin I+5. Anterior margin of spine with small retrorse hooks proximally followed by antrorse hooks distally; posterior margin of spine with strong antrorse hooks along entire length, larger than those along anterior margin. Post-cleithral process slender and pointed. Pelvic-fin rounded with six soft rays. Origin of pelvic fin in vertical line through last soft ray of dorsal-fin. Tip of adpressed pelvic-fin does not reach anal-fin. Anal fin short and rounded, its base shorter than length of adipose fin and not confluent posteriorly with caudal-fin. Anal-fin iii,6 (1), iii,7 (5), iii,8 (4), iv,6 (10), iv,7* (8), iv,8 (1).

Color in alcohol. Head darker brown in dorsal view with two yellowish V-shaped blotches near posterior nares and yellowish vertical blotch on posterior cheek below eye and reaching isthmus. Light transverse stripe, narrow and sinuous (sometimes discontinuous), on occipital region between opercular openings. Barbels pigmented with brown spots. Body tan with dark brown saddles separated by light brown interspaces. Anteriormost dark brown saddle in nuchal region (anterior to dorsal-spine origin), second below dorsal-fin base; first two saddles separated dorsally by light oval spot under dorsalfin spine, confluent ventrally above horizontal through pectoral-spine origin. Third dark brown saddle in interdorsal region and below middle of adipose-fin base continuing ventrally to about lateral line, not reaching dark blotch on base of anal fin (interrupted middorsally by longitudinally elongate pale oval at anterior insertion of adipose fin). Broad, irregularly-shaped dark brown blotch on caudal peduncle. Two small and light elliptical spots on caudal peduncle: one middorsal, located between posterior tip of adipose fin and base of caudal fin; another midventral between posterior tip of anal fin and base of caudal fin. Ventral region of body and head pale yellow. All fins hyaline with brown spots or bands. Dorsal fin hyaline, with dark brown base and broad dark brown band crossing middle portions of fin spine, rays and membranes. Adipose fin with narrow dark brown blotch at center along base flanked anteriorly and posteriorly by lighter brown blotches; distal margin pale. Pectoral fins with dark brown mottling on spines and middle portions of rays and membranes. Pelvic fins hyaline, lightly speckled with small dark spots. Caudal fin with dark brown vertical band crossing middle portions of upper and lower lobes. Anal fin with dark blotch on bases of third, fourth, fifth, sixth and seventh rays and dark brown crescentic band on middle portions of rays and membranes. Dark stripe in the axis of gill filaments.

Distribution. Microglanis leptostriatus is known from the tributaries of the middleupper course of rio São Francisco basin (figure 3).

Etymology. The name leptostriatus is derived from the Greek lepto, slender, plus striatus, stripe, in reference to the distinct light transverse stripe in the nuchal region. An adjective.

Discussion

Microglanis leptostriatus is distinguished from the other species in the genus by having pectoral and anal fins mottled or with relatively faint bands (vs. heavy dark bands in M. ater , M. pellopterygius and M. nigripinnis ); trunk with dark brown saddles (vs. mottled in M. variegatus ); caudal fin emarginate (vs. rounded in M. zonatus ); tip of pectoral spine as distinct bony point (vs. tip of pectoral spine soft, not as distinct bony point, and implanted between two teeth, one straight, pointing outwards from anterior margin and the other curved, pointing backwards from posterior margin in M. secundus (sensu Mees, 1974)); continuous portion of lateral line not reaching vertical through origin of adipose fin (vs. reaching vertical through adipose-fin origin in M. iheringi ); caudal peduncle with faint to dark blotch irregularly shaped (vs. triangular in M. poecilus ); caudal peduncle depth 11.3-17.7% of SL (vs. 8.8-10.3% of SL in M. eurystoma ); trunk short relative to head (vs. long in M. cibelae ); caudal fin lightly mottled with narrow vertical dark brown band across central portions of lobes (vs. caudal fin almost completely black with narrow vertical white band across central portions of lobes in M. malabarbai ); dark saddle beneath adipose fin not extending ventrally to anal fin as continuous bar (vs. dark bar on posterior flank continuous from base of adipose fin to that of anal fin in M. malabarbai and M. cottoides ); caudal peduncle depth 11.3-17.7% of SL (vs. caudal peduncle depth 9.8-11.4% of SL in M. parahybae ).

All examined specimens of M. leptostriatus , presented the dark stripe in the axis of gill filaments (dark stripe not observed in any other examined species of Microglanis ). The fact that all the specimens presented this character ensures that it is not a consequence of fixation or conservation.

Microglanis leptostriatus , M. garavelloi and M. parahybae are members of the M. parahybae species-complex based on their possession of the following combination of characters: body light brown with first and second dark brown saddles not surpassing pectoral-fin, with light oval spot located below dorsal-fin spine; third dark brown saddle finishing midlaterally, not reaching dark blotch on base of anal fin; and caudal fin with upper lobe slightly more developed than lower. This group occurs in coastal rivers from the rio São Francisco southward to the rio Paraíba do Sul, and in the upper rio Paraná basin.

The species of the parahybae group , as well as the whole coastal ichthyofauna, may have resulted from vicariant events in the eastern coastal region of South America during the Upper Pleistocene (Weitzman et al. 1988). During maximum glaciation sea levels were lower (marine regression), which may have contributed to the formation of an extensive coastal plain, exposing practically the whole continental platform (Secretaria de Estado do Meio Ambiente, 1996; Suguio, 1999). Hypothetically, this marine regression elongated the coastal fluvial courses and allowed for past communications among rivers in the immense plain. Such communication would facilitate the dispersion of fishes between the ancient rivers of the Brazilian coast.

However, the presence of Microglanis leptostriatus in the rio São Francisco basin does not imply, necessarily, the same history of distribution of its congeners from eastern coastal rivers. The geographical isolation of rio São Francisco population probably precedes the events of glaciation of Pleistocene and this may be an indication of an older inland distribution, when the upper rio São Francisco, upper rio Paraná and, perhaps some coastal drainages were not separated (Beurlen apud Kullander, 1983). According to Kullander (1983), in the Lower Tertiary Period, the rio Paraná drained to the north towards the current rio São Francisco and rio Tocantins; and the lower course of the rio São Francisco drained northward towards the current rio Parnaíba (figure 2) until the Quaternary Period (Pleistocene/Pliocene). Kullander still suggests that the upper courses of rio Paraná and rio São Francisco were isolated in the Middle or Upper Tertiary, resulting in the isolations of the species Cichlasoma sanctifranciscense Kullander, 1983 in the rio São Francisco, and C. paranaense Kullander, 1983 in the rio Paraná. Recently, Microglanis garavelloi from Upper Paraná was described (Shibatta & Benine, 2005) and seems to be of the parahybae group . Microglanis garavelloi is similar to M. leptostriatus , and their close relationship may corroborate the hypothesis proposed for the isolation of species of Cichlasoma (Kullander, 1983).

In agreement with Kullander (1983), we conclude that the isolation of the basins of upper courses of rio Paraná and rio São Francisco (Middle or Upper Tertiary) was previous to the isolation of rio São Francisco and rio Parnaíba basins (Quaternary). However, the absence of records of Microglanis in the rio Parnaíba basin, until the moment, disables inferences regarding the history of dispersion of the genus among these two drainages.