Pseudolaguvia tenebricosa, Ralf Britz & Carl J. Ferraris, Jr., 2003

Ralf Britz & Carl J. Ferraris, Jr., 2003, A new species of the Asian catfish genus Pseudolaguvia from Myanmar (Teleostei: Ostariophysi: Siluriformes: Erethistidae)., Zootaxa 388, pp. 1-8 : 2-7

Pseudolaguvia tenebricosa , new species

(Fig. 1a-e, Table 1)

Holotype: USNM 373293 , 29.4 mm SL; Myanmar: Kayin Division: Pathe Chaung, hill stream, 13 miles east of Taungoo , 19°01'11"N, 96°35'33"E; 39 m above sea level; 18 March 2003, R. Britz, R. Roesler & Myo Nyunt.

Paratypes: USNM 374987 , 14 specimens, 27.6-31.5 mm SL; same data as holotype ; 9 May 2003, Tin Win, Ye Hein Htet, Aung Tun Zaw, and Tin Win Htwe. Additional material: CAS 98614 , 2 specimens, 28.7-30.4 mm SL; Myanmar: Kachin Division: Nan Kwe Chaung ; 25°20.405' N 97°17.049'E; 138 m above sea level; 04 Nov. 1997, Carl J. Ferraris jr., U Tun Shwe & Mya Than Tun.

Diagnosis. Pseudolaguvia tenebricosa differs from P. tuberculata (fig. 2) (morphometric data calculated from Prashad & Mukerji's [1929] measurements) in having an adipose fin not reaching posterior insertion of dorsal fin (vs. adipose fin reaching dorsal fin), a narrower (23.8-25.1 vs. 26.7 % SL and 83.2-87.5 vs. 88.9 % HL) head, and a shorter snout (12.8-14.3 vs. 16.7 % SL and 44.7-50.6 vs. 55.6 % HL).

Description. Small species with a maximum length of 31.5 mm SL. Morphometric information for holotype and paratypes are provided in Table 1.

Dorsal-fin rays II, 6; pectoral-fin rays I, 8; pelvic-fin rays i,5; anal-fin rays iii,7, with the first ray very small, splint-like. Principal caudal-fin rays i,7,7,i.

Head dorsoventrally depressed, with subterminal mouth and broad fleshy lips. Upper lip continuing into maxillary barbels, the bases of which are connected to the sides of the head through a broad roughly triangular skin flap. Four pairs of barbels: Maxillary barbels extending to the base of the pectorals, lateral mandibular barbels only slightly shorter, medial mandibular barbels half as long as outer mandibular barbels, nasal barbels, arising from the internarial septum, reaching only two thirds the distance from naris to eye. Eye very small. Side and top of head scattered with numerous small keratinized tubercles; keratinized areas on dorsal surface of head may form short or longer irregular longitudinal lines that extend onto supraoccipital process; well-developed superfically situated scapular and humeral processes. Numerous tubercles along body forming parallel irregular series, one of which forms a straight line of light colored tubercles and runs along level of horizontal septum. Fleshy bases of adipose and anal fin also with tubercles. Rayed portions of fins without tubercles.

Pectoral fin with strong spine bearing five to seven serrae on the inner face; outer face also serrate. Dorsal spine strong with weak serrae on posterior face.

Thorax and anterior portion of abdomen flattened ventrally with large adhesive organ, consisting of 14-18 longitudinal, partly merging skin folds arranged in an elongate area, 6- 7 mm long and 3-4 mm wide, with a deep median groove. Folds extend anteriorly to isthmus, so that anterior border of adhesive organ forms a V, with its tip pointing rostrally.

Caudal fin deeply bifurcate with upper lobe in most specimens slightly longer than lober lobe; uppermost principal caudal ray extending as a short filament.

Coloration. Body brown to almost black, but underside of head and belly posteriorly of insertion of pelvic fin light beige with melanophores in median groove of adhesive organ and close to anal fin insertion. Two narrow lighter bands on side of body, one extending from posterior insertion of dorsal fin in a curve down to posterior insertion of pelvic fin, another from posterior base of adipose fin to posterior insertion of anal fin. Barbels annulated black and white. Pectoral fin with dark anterior basal area, an annulated anterior face of spine, and a distal band with hyaline tip. Dorsal fin dark brown except for light posterior seam. Pelvic fin mostly hyaline, with dark basal area and narrow dark streak subdistally. Adipose fin dark brown with lighter seam. Anal fin with dark base and narrow band that forms a half circle enclosing an almost round central hyaline area; distal parts of anal fin also hyaline. Caudal fin dark brown except for two central hyaline windows in dorsal and ventral lobes.

Etymology. From the Latin adjective tenebricosus alluding to the dark, gloomy coloration of this species.

Habitat. Pathe Chaung (fig. 3), a left bank tributary of the Sittang River, is a small hill stream, with fast running, clear water, a sandy bottom and numerous rocks and boulders. Aquatic vegetation was absent. Water temperature was 24°C, with a pH of 8.5 and a conductivity of 70 µS. All specimens were collected during the daytime. The holotype was caught with a seine among branches lying in the water, and the paratypes were collected with a battery operated electroshocker.

Discussion

Our new species closely resembles the erethistid Pseudolaguvia tuberculata and shares with that species a unique combination of two characters: (1) the presence of a distinct adhesive apparatus on the thorax possessing a median depression and consisting of longitudinal unculiferous ridges and intermittent smooth grooves and (2) well-developed scapular and cubito-humeral processes. Pseudolaguvia tenebricosa is therefore assigned to this genus.

Possession of longitudinal skin folds on the thorax that represent an adhesive apparatus facilitating life in fast flowing torrential waters, has been reported from representatives of the three erethistid genera Conta , Laguvia , and Pseudolaguvia , and the sisorid genus Glyptothorax (Hora 1922, 1930; Wu & Liu 1940; Bhatia 1950; Tilak & Husain 1975; Tilak 1976; de Pinna 1996).

When trying to resolve the generic identity of the new species described in this paper, we came to accept that the species of the genera Laguvia and Pseudolaguvia are only poorly known and the two genera are clearly in need of a revision. Hora's (1921: 739) diagnosis of the newly erected genus Laguvia mentions, among other characters, that "the skin covering the belly is corrugated, suggesting an adherent function." However, he (1921: 742) distinguished L. shawi from L. ribeiroi by the absence of a thoracic adhesive apparatus in the former and its presence in the latter. Hora (1921: 742) described this apparatus in L. ribeiroi as "oblique grooves and ridges which form a V-shaped adhesive apparatus similar to that found in the genus Glyptothorax but not so well-developed" and Hora (1922: fig. 7a) figured well developed skin folds on the thorax of Laguvia sp.

Subsequently, Shaw & Shebbeare (1937: 105) noted that in L. shawi , contra Hora (1921), there is "a rudimentary adhesive apparatus on the thorax of fresh specimens." [These authors (104: fig. 106) also figure a specimen of L. ribeiroi in lateral and ventral view with an adhesive apparatus clearly recognizable in the latter. This figure is cited as having been copied from “Rec. Ind. Mus.”, but the original description of L. ribeiroi by Hora does not contain a ventral view of the species.]

Menon (1955) synonymized the genus Laguvia with Glyptothorax , because he found that the characters Hora (1921) used to distinguish Laguvia were also present in Glyptothorax , specifically mentioning P. tuberculata (as G. tuberculatus ) in this context.

Misra (1976: 247) listed Laguvia as a valid genus with 3 species and noted a "poorly developed adhesive apparatus composed of longitudinal plaits of skin" in its generic diagnosis and in the three species descriptions, implying that such an apparatus is present in all Laguvia species. Tilak and Hussain (1975) mention also an adhesive apparatus in L. kapuri . Arunkumar (2000) recently described a fifth species in the genus, Laguvia manipurensis , but did not mention the adhesive thoracic apparatus.

Misra (1976) created the new genus Pseudolaguvia to accommodate Glyptothorax tuberculatus . Misra's (1976) description of the genus contained mainly characters that are not diagnostic, but are instead widespread among erethistids and sisorids. However, he (p. 253) cited two characters in which the genus differed from other closely allied genera: "1. A well developed thoracic adhesive apparatus which is considerably longer than broad with an elongated depression in the middle", and "2. A contiguous adipose dorsal fin with the rayed dorsal fin." The genus Pseudolaguvia has remained monotypic, comprising only P. tuberculata from Sankha stream between Mogaung and Kamaing, Upper Myanmar.

Our new species, Pseudolaguvia tenebricosa , thus shares with P. tuberculata a well developed adhesive apparatus with a median depression, but lacks the second character of P. tuberculata , an adipose fin that is contiguous with the dorsal fin. We want to point out here that the difference between the "well developed adhesive apparatus" in Pseudolaguvia (Prashad & Mukerji 1929; Misra 1976; Jayaram 1979, 1999; Talwar & Jhingran 1991) and the "poorly developed adhesive apparatus" in some species of Laguvia (Hora 1921; Misra 1976; Jayaram 1979, 1999; Talwar & Jhingran 1991) may not be a clear-cut character, as the scanning-electron-micrographs of L. ribeiroi published by de Pinna (1996) show a distinct adhesive apparatus, however without the median depression typical of Pseudolaguvia . In spite of the vague generic diagnosis of Pseudolaguvia , the most reasonable approach to us right now is to assign the new species to this genus on the basis of its close resemblance to P. tuberculata and especially the shared presence of a conspicuous median depression in the well developed adhesive apparatus.

De Pinna (1996) listed erethistid specimens from Koilla Khal, Chittagong, Bangladesh (UMMZ 209010) as Pseudolaguvia tuberculata . However, he (personal communication, 2003) acknowledged that his identification may have been incorrect and Heok Hee Ng (personal communication, 2003), currently studying these specimens, concluded that they represent a new species whose generic assignment is not clear. Because the specimens are under study elsewhere, we cannot comment on them further, but only stress again that the group appears to be in need of a thorough revision.

According to de Pinna (1996), the adhesive apparatus of the erethistid genera Laguvia , Pseudolaguvia , and Conta has evolved independently from the remarkably similar apparatus of Glyptothorax . The latter genus was placed in the family Sisoridae by de Pinna (1996) and hypothesized to be the closest relative of a taxon consisting of the genus Pseudecheneis and the subtribe Glyptosternina. The adhesive apparatus of Pseudecheneis consists of transverse, not longitudinal, ridges and grooves and an adhesive apparatus is absent from members of the Glyptosternina, which is composed of the genera Glyptosternon , Glaridoglanis , Oreoglanis , Exostoma , Myersglanis , Coraglanis , Euchiloglanis , and Pseudexostoma . In de Pinna's (1996) scenario, the independent development of an adhesive apparatus of Glyptothorax similar in appearance to that in the erethistids was modified into the apparatus with transverse ridges in the lineage of Pseudecheneis and lost in the lineage leading to the Glyptosternina. This convoluted scenario and, especially, the apparent evolutionary loss of an adhesive apparatus seems surprising, as all species of Glyptosternina occur in fast flowing waters, in which such an adhesive apparatus would certainly appear to have an important biological role.