Pseudecheneis maurus , Heok Hee Ng & Heok Hui Tan, 2007
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Pseudecheneis maurus sp. nov.
Type material. Holotype: ZRC 50638, 54.8 mm SL; Vietnam: Da Nang province, Song Thuy Loan drainage, Ban Na hill station, Cat Lon stream, ca. 9 km along road before summit , 16°0'39.2"N 108°1'2.6"E, 722 m asl ; H. H. Tan & A. D. Tran, 28 February 2005.GoogleMaps
Diagnosis. Pseudecheneis maurus is distinguished from all congeners in having a shorter adipose-fin base (1.2 times length of anal-fin base vs. 1.5-2.0 times; 15.7% SL vs. 17.6-30.6), (except for P. sympelvica ) thoracic adhesive apparatus with sulcae not meeting (vs. meeting) at midline and (except for P. immaculata ) in lacking (vs. having) distinct pale spots on the body. It further differs from P. immaculata in having a shorter pectoral fin (24.3% SL vs. 32.0) and shorter and deeper caudal peduncle (length 21.2% SL vs. 28.8; depth 6.0% SL vs. 4.0). from. It differs from P. paviei ZBK and P. sympelvica in having an elongate body with 38 vertebrae (vs. short body with 33-35 vertebrae) and from P. sympelvica in having separate (vs. fused) pelvic fins.
Description. Biometric data as in Table 1. Head and abdominal region narrow and strongly depressed. Dorsal profile rising gently from tip of snout to origin of dorsal fin, then almost horizontal or sloping very gently ventrally to end of caudal peduncle. Ventral profile horizontal to anal-fin base, then sloping very gently dorsally to end of caudal peduncle. Caudal peduncle long and moderately compressed. Anus and urogenital openings located at posteriormost extent of pelvic fin. Skin smooth, tuberculate in some areas. Lateral line complete and midlateral. Vertebrae 19+19=38.
Head acutely rounded when viewed from above. Gill openings moderate, extending from posttemporal region to base of first pectoral-fin element. Head covered with thick, tuberculate skin. Ventral surface of head with unculiferous collar on distal margin of branchiostegal membrane immediately anterior to thoracic adhesive apparatus.
Thoracic adhesive apparatus consisting of 13 transverse ridges (laminae) separated by grooves (sulcae); sulcae not meeting at midline of adhesive apparatus. Adhesive apparatus extending from immediately posterior to collar on distal margin of branchiostegal membrane to immediately posterior to level of last pectoralfin ray.
Barbels flattened, and in four pairs. Maxillary barbel with ventral surface densely covered with papillae, and pointed tip; barbel extending about two-thirds of distance between its base and base of first pectoral-fin element. Distal half of barbel attached to snout via large, thin flap of skin. Nasal barbel with small flap of thin skin fringing posterior margin and extending midway to distance between posterior nares and anterior orbital margin. Inner mandibular-barbel densely covered with papillae; origin close to midline, extending to collar on distal margin of branchiostegal membrane. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to level of anterior orbital margin. Eye small and almost rounded, subcutaneous and located on dorsal surface of head.
Mouth inferior, with moderately broad, thin papillate lips. Rictal lobe large and papillate. Premaxillary tooth band not exposed when mouth is closed. Premaxillary teeth short and conical, arranged in irregular rows on a moderately large quadrangular patch. Dentary teeth long, thin and somewhat rounded at tip; arranged in irregular rows on two separated, roughly triangular patches.
Dorsal-fin origin located at point through anterior third of body. First and second dorsal fin-ray elements not ossified, bearing i,6 rays, and fin margin straight. Adipose fin with very short base, 1.2 times anal-fin base length; located in middle third of postdorsal region. Adipose fin margin gently convex; posterior end deeply incised. Caudal fin forked, with i,7,8,i principal rays; procurrent rays symmetrical and extend only slightly anterior to fin base. Anal fin with short base extending less than half of adipose fin-base length and iii,7,i rays. Anal fin margin almost straight.
Pelvic-fin origin at vertical through second or third dorsal fin-ray base. Pelvic fin greatly enlarged, extending to base of first anal-fin ray. Anterior fin margin strongly convex, first element broadened and with regular striae on ventral surface; with i,5 rays. Pectoral fin greatly enlarged and with convex anterior margin, reaching to just beyond pelvic-fin base. First element not ossified, broadened and with regular striae on ventral surface; fin with i,1 1,i rays.
Coloration. In 70% ethanol: chestnut brown on dorsal and lateral surfaces of head and body, fading to light brown on ventral region. Dorsal surfaces of head and body with indistinct light brown patches on supraoccipital spine and immediately anterior to dorsal-spine base. Lateral surfaces of body with very faint light brown patches: one patch immediately posterior to last dorsal-fin ray and an elongate ovate spots on side of body immediately ventral to origin of adipose fin. Dorsal and anal fins with chestnut brown base and subdistal band. Adipose fin chestnut brown, with light brown anterior margin and margin along posterior twothirds of fin. Caudal fin chestnut brown, with small hyaline spot on lobes near horizontal midline and hyaline distal margin. Dorsal surfaces of pectoral and pelvic fin bases chestnut brown, with hyaline distal margin; ventral surfaces hyaline. Maxillary and nasal barbels chestnut brown dorsally and light brown ventrally.
Distribution. Presently known only from the Song Thuy Loan River drainage (of which the Cat Lon stream is a tributary) that drains the eastern face of the Annam Cordillera in central Vietnam (Fig. 2).
Habitat. The single specimen was obtained from a riffle zone of a small hill stream (ca 2-4 m wide, ca 10-30 cm deep). The bottom consists of fine gravel and granitic rocks, with exposed boulders along the banks and streamline (Fig. 3). The water was swift flowing and cool (ca 24 °C). No other fish were obtained from this habitat, although at least six species of amphibian tadpoles were present (unpub. data).
Etymology. From the Greek mauros, meaning dark, in reference to the absence of distinct pale spots on the body of this species. Used as a noun in apposition.
The relatively short adipose-fin base of P. maurus easily distinguishes the species from congeners. The thoracic adhesive apparatus of P. maurus is also distinctive, with the sulcae not meeting at the midline. Only P. sympelvica has an adhesive apparatus with a similar morphology, but it can be distinguished from P. maurus by the characters mentioned in the diagnosis. Pseudecheneis maurus represents the first record of the genus in river drainages draining the eastern face of the Annam Cordillera. The most geographically proximate species is P. sympelvica , which is found in the Nam Theun river drainage (part of the Mekong River drainage) that drains the western face of the Annam Cordillera (ca. 400 km to the northwest). However, in addition to the different vertebral counts, fused pelvic fins, different color pattern and longer adipose fin base of P. sympelvica as outlined in the diagnosis, P. sympelvica further differs from P. maurus in having a more slender caudal peduncle (depth 4.7-4.8% SL vs. 6.0).
The description of Pseudecheneis maurus from only a single specimen (only one specimen was obtained in spite of intensive sampling lasting about an hour on each of three separate occasions at the type locality) is justifiable in this case because of the clear differences in the morphology of this species from all its congeners. These differences are present in morphological characters (e.g. length of adipose-fin base, depth of caudal peduncle) that have been shown to be useful for diagnosing other congeners (Ng, 2006a; 2006b; Ng & Edds, 2005). Furthermore, P. maurus is known from an area where the genus has not been previously recorded and where considerable endemicity in the freshwater ichthyofauna has been demonstrated (e.g. Freyhof & Serov, 2000).
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