Oreoglanis majusculus, Linthoingambi & Vishwanath, 2011

Linthoingambi, I. & Vishwanath, W., 2011, Oreoglanis majusculus, a new glyptosternine catfish from Arunachal Pradesh, India (Teleostei: Sisoridae), Zootaxa 2754 (1), pp. 60-66 : 61-65

Oreoglanis majusculus , sp. nov.

( Fig. 1a–c )

Holotype. MUMF 6294 , 64.5 mm SL; India: Arunachal Pradesh state: Kameng River, at Rupa , 27°12’38”N; 92°24’06”; K. Nebeshwar, 5 November 2005.

Paratypes. ( All from Brahmaputra basin of Arunachal Pradesh) MUMF 6195-6197 , 3 , 41.6 –76.0 mm SL; same data as holotype. RGUMF 0128 , 7 , 35.0–75.0 mm SL; India: Arunachal Pradesh: Kameng River , at Rupa, 27°12’38”N; 92°24’06”; Kenjum Bagra, 21 August 2005 .

Diagnosis. Oreoglanis majusculus , a species of the O. siamensis group sensu ( Ng & Rainboth, 2001) is distinguished from all its congeners in having the posterior margin of the maxillary barbel villiform (vs. entire, crenulate or lobulate). It further differs from O. macropterus and O. insignis in having a caudal-peduncle depth of 6.1–6.4% SL (vs. 8.0–8.7 and 3.0–3.8, respectively); from O. setiger in having a caudal-peduncle length of 18.0–21.3% SL (vs. 26.1–28.8); from O. siamensis in having the posterior margin of the lower lip entire (vs. lobulated); from O. jingdongensis in having the caudal-fin lobes equal (vs. lower lobe longer); from O. immaculatus in having pectoral-fin rays 20 (vs. 17–18) and the lower-lip margin entire (vs. slightly indented); from O. heteropogon , O. laciniosus and O. sudarai in having posterior margin of lower lip entire (vs. lobulated); and from O. suraswadii in having posterior margin of lower lip entire (vs. with indistinct projections).

Description. Table 1 presents morphometric data. Head and body moderately broad, strongly depressed. Mouth inferior; lips broad, thin, papillate. Lower lip modified into a labial fold, a median notch present; lower-lip posterior margin entire. Post-labial groove on lower jaw present, continuous. Teeth in upper jaw pointed, in a large broad band separated by a small median indentation, band margins laterally rounded; teeth in lower jaw in two well-separated patches of roughly triangular shape, of two kinds: anterior teeth truncate-spatulate, with curved inner face; posterior teeth pointed (like those of upper jaw). Eyes small, dorsolaterally orientated, subcutaneous. Anterior nostril separated from posterior nostril by nasal-barbel base. Gill openings narrow, arched, extending to middle of pectoral-fin base.

Barbels in four pairs. Maxillary barbel flattened, with a surrounding flap of skin and rounded tip, its ventral surface with numerous plicae, posterior edge with villiform projections in a single row ( Fig. 2 ). Nasal barbel short, extending to middle of distance between its base and proximal margin of eye. Outer mandibular barbel extends to level of anterior base of pectoral fin. Inner mandibular barbel arising from postlabial groove at same level as origin of outer mandibular barbel.

Dorsal-fin bearing i, 6 rays, its origin above middle of pectoral fin, posterior end of fin base above middle of pelvic-fin base. Adipose fin rising gradually, terminating above middle of caudal peduncle length, its posterior margin acute. Pectoral fin bearing i, 20 rays, greatly enlarged, overlapping pelvic fin up to anterior half of fin base, first ray greatly flattened, with numerous plicae on ventral surface. Pelvic-fin bearing i, 5 rays, its origin level with middle of dorsal-fin base, extending to level of adipose-fin origin, touching vent. Anal-fin bearing ii, 3 rays, its origin level with middle of adipose-fin base. Caudal fin emarginate, with 7+8 principal rays.

Males with two flaps of skin on either side of anus, a small genital papilla located immediately posterior to anus in a U-shaped depression. Females with a small genital papilla located in a U-shaped depression immediately behind anus ( Fig. 3 ).

Coloration. In formalin, brown on dorsal and lateral surfaces of head and body, light yellow on ventral region. Fins brownish, caudal-fin base with a black blotch.

Etymology. From the Latin majusculus, meaning somewhat greater, in reference to the large paired fins; an adjective.

Distribution. Oreoglanis majusculus is presently known only from the type locality: the Kameng River in Arunachal Pradesh (State), Brahmaputra drainage, India ( Fig. 4 ).

Discussion. Oreoglanis majusculus differs from all its congeners in having the posterior margin of the maxillary barbel villiform, vs. entire, crenulate or lobulate in other members of the genus. The new species further differs from O. frenatus in having the adipose fin separated from (vs. confluent with) the upper principal rays of caudal fin; and principal rays on lower and upper caudal-fin lobes equal (vs. those of lower lobe longer). It further differs from O. delacouri , O. lepturus , O. infulatus , O. hypsiurus and O. macronemus in having a deeper caudal peduncle, its height 6.1–6.4% SL (vs. 2.1–4.9) and, except for O. macronemus , a longer head, its length 24.1–27.4% SL (vs. 18.9–24.7). The new species also differs from O. macronemus in having the prepelvic length 36.0–38.0% SL (vs. 39.6–43.7); pelvic-fin length 22.5–26.0 % SL (vs. 16.0–17.9); adipose-fin base length 29.3–34.1% SL, (vs. 25.7– 29.9); and inner mandibular barbel length 12.0–14.4%HL, (vs. 17.8–27.4).

The new species differs from O. insignis in having a caudal-peduncle length of 18.0–21.3% SL (vs. 22.7–27.7), and a nasal-barbel length of 20.0–23.2% HL (vs. 8.3–17.5); from O. setiger and O. jingdongensis in having the interdorsal distance 15.0–18.7% SL (vs. 13.5–13.6 and 20.5–29.1), respectively; from O. siamensis in having the tip of the maxillary barbel rounded (vs. pointed), an interorbital distance of 17.2–33.0% HL (vs. 23.1–26.9); and from O. immaculatus in having the lower-lip margin entire (vs. slightly indented).

The new species further differs from O. laciniosus , O. sudarai and O. suraswadii in having posterior edge of the maxillary barbel villiform (vs. smooth); and from O. heteropogon in having posterior edge of the maxillary barbell villiform (vs. crenulate). It also differs from O. heteropogon and O. sudarai in having the pectoral fin extending beyond the pelvic-fin origin (vs. not reaching pelvic-fin origin); nasal barbel extending midway between barbel base and anterior margin of eye (vs. up to anterior margin of eye); and maxillary-barbel tip rounded (vs. pointed); from O. laciniosus in having the caudal-peduncle depth 5.6–7.5 (vs. 2.8–3.4) times in its length; from O. suraswadii in having the caudal fin lunate (vs. emarginate), its branched rays 5+6 or 6+6 (vs. 7+8), and caudal-peduncle depth 4.5–6.3 (vs. 2.8–3.4) in its length.

It differs from O. colurus , O. nakasathiani , O. tenuicauda and O. vicinus in having the posterior margin of the lower lip entire (vs. with lobulate projections); the adipose fin separated from the upper procurrent rays of the caudal fin (vs. confluent, except in O. nakasathiani ); and the caudal fin emarginate (vs. lunate, except in O. tenuicauda ). Ng & Rainboth (2001) reported members of the genus to have variously crenulate, lobulate, laciniate and entire maxillary-barbel posterior margins. In the new species, the barbel bears distinct villiform projections in the posterior margin. Thus, five kinds of maxillary-barbel posterior margins are now known. They also divided the representatives of the genus into two species groups, the O. delacouri group and the O. siamensis group, based on the presence or absence, respectively, of a median notch in the lower lip, an interrupted posterior margin of the lower lip, and an emarginate caudal fin. Later, Kong et al. (2007) redefined the two species groups solely on the basis of lower-lip morphology. We follow the latter to define the two species groups. Oreoglanis majusculus belongs to the O. siamensis group as it has a median notch on the lower lip and an entire lower-lip posterior margin.

Figures of all valid Oreoglanis species ( Ng & Kottelat, 1999, 2000; Ng & Rainboth, 2001; Ng & Freyhof, 2001; Ng, 2004a; Kong et al., 2007; Vidthayanon et al., 2009) show the vent to be situated substantially anterior to the anal-fin origin, i.e., about the middle of the distance between the pelvic-fin and anal-fin bases (i.e., distance between vent and anal-fin origin about 50% of distance between pelvic-fin and anal-fin origins). In our series of O. majusculus (n=11), the pelvic fin always reaches the vent. In the figures of valid Pseudexostoma species (as observed from figures in Zhou et al., 2007), the vent is placed a little in advance of the anal fin, i.e., distance between vent and anal-fin origins about 15–18% of distance between pelvic-fin and anal-fin origins, with the pelvic fin never reaching the vent. Examination of positions of vent and extent of pelvic fins of larger series of specimens would be interesting. We have been able to examine a few representatives of glyptosternine genera, viz., Glyptosternon akhtari , G. reticulatum , Myersglanis jayarami , Parachiloglanis hodgarti and Pareuchiloglanis kamengensis . Of these, P. hodgarti has the most posteriorly placed vent, i.e., distance between vent and anal-fin origin about 13% of distance between pelvic-fin and anal-fin origins. In Exostoma and Glyptosternon , the distance between the vent and the anal-fin origin is 30–33% the distance between the pelvic-fin and anal-fin origins. However, as the position of vent is variable in Pareuchiloglanis (as observed from figures in Ng & Kottelat, 2000; Ng, 2004b; Li et al., 2007 and the present study), this character may be useful only for discriminating between species.

This paper extends the range of the genus Oreoglanis to the Brahmaputra basin and represents its first record from India. Ng’s (2004a) statement that the genus is distributed throughout India needs clarification as the literature appears to show no record of the genus in Indian waters.

Figures

FIGURE 1. Oreoglanis majusculus: A. lateral view; B. dorsal view; C. ventral view.

FIGURE 2. Lower lip of Oreoglanis majusculus, showing villiform posterior margin of maxillary barbel.

FIGURE 3. Genitalia of Oreoglanis majusculus: A. male; B. female.

FIGURE 4. Map of Arunachal Pradesh State, India, showing type locality of Oreoglanis majusculus.