Exostoma dulongensis, Luo & Chen, 2020

Luo, Zhaojun & Chen, Xiaoyong, 2020, Exostoma dulongensis a new glyptosternine catfish from the Irrawaddy basin Yunnan, China (Siluriformes: Sisoridae), Zootaxa 4802 (1), pp. 99-110 : 100-106

Exostoma dulongensis sp. nov.

( Figs. 1-3 )

Exostoma labiatum (non McClelland): Chu & Chen, 1990 (Bapo, Irrawaddy basin); Chu & Mo, in Chu, Zheng & Dai et al, 1999 (Bapo, Irrawaddy basin); Chen X.Y, 2013 (Bapo, Irrawaddy basin) .

Holotype. KIZ 20040010 , 91.7 mm SL, China: Yunnan Province, Lushui County, Pianma Township; Xiaojiang River main stream at Gulangba village , 26°5’7.9”N, 98°35’12.7”E, collected by Xiao-Yong Chen, Jian Yang, Fei Wu, and staff of Gaoligong Mountain National Nature Reserve Management Bureau, 9 April 2004.

Paratypes. KIZ 20040001–20040009 , KIZ 20040011–20040014 , KIZ 05090, KIZ05095–05096 , 16 ex., 79.9– 99.0 mm SL, collected with holotype . KIZ 05015–05016 , 2 ex., 79.1–89.2 mm SL, collected at Wuzhong River , tributary of Xiaojiang River, 2 April 2004 , collected by Xiao-Yong Chen, Jian Yang, Fei Wu. KIZ 20041029078 , 1 ex., 72.0 mm SL, 29 October 2004 . KIZ 20041105058 , KIZ 20041105060 , KIZ 20041105062 , 3 ex., 79.2–112.1 mm SL, 5 November 2004 . KIZ 20041107030–20041107031 , 2 ex., 92.4–101.7 mm SL, 7 November 2004 . KIZ 20041107172–20041107173 , 2 ex., 61.0–79.0 mm SL, 7 November 2004 . KIZ 20041108157 , KIZ 20041108159 , 2 ex., 82.6–110.0 mm SL, 8 November 2004 . KIZ 20041114091–20041114092 , 2 ex., 53.6–68.7 mm SL, 14 November 2004 . KIZ 20041114065 , 1 ex., 79.4 mm SL, 14 November 2004 . Specimens from Dulongjiang River were collected by Zi-Ming Chen and Xiao-Fu Pan .

Non-types. KIZ 05081, 90.4 mm SL, collected at Xiaojiang River on 7 April 2004, collected by Xiao-Yong Chen, Jian Yang, Fei Wu , and staff of Gaoligong Mountain National Nature Reserve Management Bureau . KIZ 07466–07467 , 07483 , uncataloged, 15 ex., collected at Dulongjiang River on 17 August 2007 . KIZ 05045–05047 , uncataloged, 24 ex., collected at Dulongjiang River on 20 August 2007 . Uncataloged , 65 ex., collected at Dulongjiang River on 22 August 2007 . KIZ 07599, uncataloged, 35 ex., collected at Dulongjiang River on 24 August 2007 . Uncataloged , 2 ex., collected at Dulongjiang River on 26 August 2007 .

Diagnosis. Adipose fin confluent with caudal fin and without incision; tip of pelvic fin far from anus when depressed; caudal fin weakly forked; nasal barbel reaching or surpassing posterior edge of eye; parallel striae on anterolateral surface of lips; 40–43 vertebrae; pectoral fin extending to vicinity of dorsal-fin origin. Preanal length 70.9%–80.1% SL; dorsal-fin base length 6.4%–10.6% SL; pectoral to pelvic distance 19.6%–25.5% SL; nasal barbel length 32.1%–46.3% HL.

Description. Morphometric and meristic data are given in Table 1.

Head and body slightly depressed, and paired fins greatly enlarged to form elongate ovoid adhesive disc with body. Snout blunt and slightly depressed. Rostral margin rounded in dorsal view, moderately curved in lateral view. Dorsal profile rising slightly and evenly from internarial region to origin of dorsal fin, remaining straight to end of adipose-fin base origin, then gradually sloping downwards to caudal peduncle. Ventral profile rising gradually to caudal peduncle. Eyes tiny, subcutaneous, located dorsolaterally.

Rostral cap with non-prominent grooves in middle of anterior edge, ventrally parallel striae on anterolateral surface of lips. Anus and urogenital openings located behind posterior margin of adpressed pelvic fin.

Homodont dentition with oar-shaped teeth, sparsely located in both jaws, deeply inserted in skin. Tooth bands on both jaws apparently visible, whether mouth open or closed. Papillae above mouth. Middle of upper and lower jaws without distinctly separated and interrupted groove.

Barbels in four pairs, flattened. Nasal barbel long, reaching or beyond posterior orbital margin. Maxillary barbel much longer than nasal barbel, far surpassing posterior of pectoral-fin base. Tips slightly pointed. Rows of parallel striae on ventral surface. Two pairs of mandibular barbels, short. Inner mandibular barbel, shortest, originating from notch on posterior margin of lower lip. Outer mandibular barbel longer than inner ones, situated on lower lip. Tips reaching or surpassing first pectoral-fin base.

Dorsal-fin rays i, 6 (32 specimens), without spine, originating from first third of body, several conical tubercles on first unbranched ray, absent on branched rays. Adipose fin confluent with caudal fin and without incision. Pair of pectoral fins larger than other fins, i, 10 (18) or i, 11 (14) rays, without spine, rays with numerous regular conical tubercles. First unbranched rays thick and fleshy, many parallel rows of striae on ventral surface. Tips of pectoral fin not reaching origin of pelvic fin but exceeding vicinity of dorsal-fin origin. Pelvic-fin rays i, 5 (32), first unbranched rays thick and fleshy, many parallel rows of striae on ventral surface, origin almost reaching 4/5 of dorsal fin base, tip of pelvic fin far from anus. Anal-fin rays i, 4 (4) or i, 5 (28), located posterior to anus and urogenital openings. Length of anal fin shorter than anal to caudal fin distance (10.7% – 15.3% SL vs. 17.6% – 25.5%), distance of pelvic to anal fin longer than anal to caudal fin. Caudal-fin rays i, 7, 7, i (1), i, 7, 8, i (2), i, 8, 8, i (21), i, 8, 9, i (7) or i, 9, 9, i (1). Lateral-line complete.

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Coloration. In 70% ethanol: Dorsal and lateral surfaces of head and body brownish gray. Dorsal fin brownish gray, brown at base. Lateral surfaces of unbranched pectoral fin and pelvic fin rays light brown, tips of pectoral and pelvic fins white yellow. Adipose fin base dark brown, top edge transparent and yellowish. Caudal peduncle base dark brown, margin of upper and lower caudal fin rays light yellow, tip of middle caudal fin rays white yellow, middle of caudal fin light brown. Ventral surfaces of specimen light yellow. Whole anal fin region pale yellow. Dorsal surface of nasal barbel dark brown, maxillary barbel pale yellow, ventral surface pale yellow. Mandibular barbels pale yellow.

In life ( Figure 3 ): Lateral surface of body red gray, head pale yellow. Dorsal and adipose fin bases dark brown. Dorsal fin yellowish, pectoral and pelvic fins light red. Dorsal, pectoral, and pelvic fins and head with many white conical tubercles. Caudal peduncle base and margin of upper and lower caudal fin rays red gray, tip and middle of caudal fin rays bright white. Nasal and maxillary barbels bright white.

Distribution and habitat. This species is currently known from the Xiaojiang River and Dulongjiang River, tributaries of N’mai Hka River in the Irrawaddy basin, Yunnan Province, China ( Figure 4 ). The holotype was collected from deep water (> 2 m deep) in fast-flowing water of Xiaojiang River ( Figure 5 ). The elevation was 1561 m, water temperature was 11.0 °C, and water pH was 5.4. The bottom substrate consisted of rocks, sand, and cobbles.

Etymology. The specific name derived from the locality of the new species in Dulongjiang River, adjectival.

Discussion

Exostoma dulongensis sp. nov. is similar to E. gaoligongense , E. ericinum , E. chaudhurii , E. vinciguerrae , E. berdmorei , E. peregrinator , E. sawmteai by adipose fin confluent with caudal fin vs. adipose fin separated from caudal fin in E. kottelati , E. tenuicaudata , E. stuarti , E. mangdechhuensis , E. labiatum , E. tibetana , E. barakensis , E. sectile , E. effrenum . Exostoma dulongensis sp. nov., E. ericinum , E. chaudhurii , E. tenuicaudata can be distinguished from E. gaoligongense , E. vinciguerrae , E. berdmorei , E. peregrinator , E. kottelati , E. stuarti , E. mangdechhuensis , E. labiatum , E. tibetana , E. sectile , E. effrenum by having parallel striae on anterolateral surface of lips vs. having parallel and rounded striae or only rounded striae on anterolateral surface of lips.

Exostoma dulongensis sp. nov. is most similar to E. ericinum for having parallel striae on anterolateral surface of lips ( Figure 6 ), adipose fin confluent with caudal fin, caudal fin weakly forked, sharing similar body shape and number of vertebrae. But can be distinguished from E. ericinum by tip of pelvic fin far from (vs. reaching) anus when depressed; nasal barbel reaching or surpassing posterior edge of orbit vs. just reaching middle of orbit; greater preanal length (70.9%–80.1% SL vs. 67.7%–70.5%); and longer dorsal to adipose distance (13.5%–23.8% SL vs. 8.0%–12.0%). Exostoma dulongensis sp. nov. and E. ericinum are both from the Irrawaddy basin. The other four species from the Irrawaddy basin, i.e., E. stuarti , E. chaudhurii , E. vinciguerrae , E. sectile have been described successively ( Kottelat, 2013; Ng 2018; Ng & Kottelat 2018). Exostoma dulongensis sp. nov. can be further distinguished from E. stuarti by adipose fin confluent with (vs. distinctly separate from) dorsal procurrent caudal-fin rays; and relatively larger (vs. relatively smaller). Exostoma dulongensis sp. nov. can be further distinguished from E. chaudhurii by tip of pelvic fin far from (vs. reaching) anus when depressed; and nasal barbel reaching or surpassing posterior edge of orbit (vs. not reaching or just reaching middle of orbit). The new species further differs from E. vinciguerrae by tip of outer mandibular barbel reaching or surpassing (vs. not reaching) first pectoral fin base; and parallel (vs. only rounded) striae on anterolateral surface of lips ( Figure 6 ). Exostoma dulongensis sp. nov. can be distinguished from E. sectile by adipose fin confluent with (vs. distinctly separate from) caudal fin and without incision (vs. with strong incision); and having parallel (vs. only rounded) striae on anterolateral surface of lips.

Exostoma labiatum , E. tenuicaudata , E. mangdechhuensis , E. tibetana , and E. kottelati are from the Brahmaputra River basin. Exostoma dulongensis sp. nov. can be further distinguished from E. labiatum by having parallel (vs. only rounded) striae on anterolateral surface of lips; greater pectoral–pelvic distance (19.6%–25.5% SL vs. 17.7%– 18.8); greater pelvic fin length (16.0%–19.3% SL vs. 14.1%–16.0%); and more vertebrae (40–43 vs. 38). Exostoma dulongensis sp. nov. can be further distinguished from E. tenuicaudata by outer mandibular barbel reaching or surpassing (vs. not reaching) first pectoral fin base; deeper body (depth at anus 11.5%–15.5% SL vs. 9.6%–11.3%); and greater preanal length (70.9%–80.1% SL vs. 68.1%–70.1%). Exostoma dulongensis sp. nov. can be further distinguished from E. mangdechhuensis by adipose fin confluent with caudal fin (vs. conspicuous anteriorly projected notch on posterior connection of adipose fin to caudal peduncle); shorter maxillary barbel length (54.1%–89.8% HL vs. 91.5%–101.6%); and longer nasal barbel length (32.1%–46.3% HL vs. 23.1%–30.1%). Exostoma dulongensis sp. nov. further differs from E. tibetana by adipose fin confluent with caudal fin and without incision (vs. adipose fin separate from upper procurrent caudal-fin rays and incised at posterior extremity of its base); having parallel (vs. only rounded) striae on anterolateral surface of lips. The new species can be distinguished from E. kottelati by adipose fin confluent with caudal fin (vs. adipose fin distinctly separate from dorsal procurrent caudal-fin rays); parallel (vs. parallel and rounded) striae on anterolateral surface of lips; and more vertebrae (40–43 vs. 39).

Exostoma barakensis and E. sawmteai are both from the Surma-Meghna basin. Exostoma dulongensis sp. nov. differs from E. barakensis by posterior end of adipose fin adnate with dorsal procurrent caudal-fin rays (vs. separated by distinct notch); and greater nasal barbel length (32.1%–46.3% HL vs. 27.2%–32.0%). The new species can be further distinguished from E. sawmteai by more vertebrae (40–43 vs. 38–39); weakly forked (vs. lunate) caudal fin; shorter dorsal fin base length (6.4%–10.6% SL vs. 12.4%–13.5%); and shorter pectoral-pelvic distance (19.6%–25.5% SL vs. 28.6%–32.8%).

Exostoma effrenum and E. peregrinator are both from the Chao Phraya River basin. Exostoma dulongensis sp. nov. can be further distinguished from E. effrenum by adipose fin confluent with (vs. distinctly separate from) caudal fin without incision (vs. with); tip of pelvic fin not reaching (vs. reaching) anus when depressed; tip of outer mandibular barbel reaching or surpassing (vs. not reaching) first pectoral fin base; more vertebrae (40–43 vs. 36–38); shorter dorsal-fin base length (6.4%–10.6% SL vs. 12.9%–15.3%); shorter pectoral to pelvic distance (19.6%–25.5% SL vs. 29.5%–32.9%); and greater dorsal to adipose distance (13.5%–23.8% SL vs. 10.3%–12.3%). Exostoma dulongensis sp. nov. can be further distinguished from E. peregrinator by tip of pelvic fin not reaching (vs. reaching) anus when depressed; weakly forked (vs. lunate) caudal fin; more vertebrae (40–43 vs. 36–38); short- er dorsal-fin base length (6.4%–10.6% SL vs. 12.3%–13.8%); shorter pectoral to pelvic distance (19.6%–25.5% SL vs. 29.9%–35.3%); and greater dorsal to adipose distance (13.5%–23.8% SL vs. 8.2%–13.1%).

Exostoma berdmorei and E. gaoligongense are from the Salween drainage. Exostoma dulongensis sp. nov. differs from E. berdmorei by longer nasal barbel reaching or surpassing posterior edge of orbit (vs. reaching middle of orbit); longer outer mandibular barbel reaching or surpassing first pectoral-fin base (vs. reaching 2/3 of distance between its base and base of first pectoral-fin ray); tip of pelvic fin not reaching (vs. reaching) anus when depressed; more vertebrae (40–43 vs. 36–37); shorter dorsal-fin base length (6.4%–10.6% SL vs. 13.1%–13.3%); shorter pectoral to pelvic distance (19.6%–25.5% SL vs. 32.8%–36.0%); and greater dorsal to adipose distance (13.5%–23.8% SL vs. 9.2%–11.7%). Exostoma dulongensis sp. nov. can be further distinguished from E. gaoligongense by pelvic fin not reaching (vs. reaching) anus; caudal fin weakly forked (vs. emarginate); shorter pectoral to pelvic distance (19.6%–25.5% SL vs. 26.9%–31.6%); and parallel (vs. parallel and rounded) striae on anterolateral surface of lips ( Figure 6 ).

Figures

FIGURE 1. Exostoma dulongensis sp. nov., holotype, KIZ 20040010, 91.7 mm SL: Dorsal, lateral, and ventral views. Photos by Tao Qin.

FIGURE 2. Radiograph of Exostoma dulongensis sp. nov., paratype, KIZ 20041107030.

FIGURE 3. Exostoma dulongensis sp. nov., paratype, KIZ 05096, 81.0 mm SL. Lateral view showing coloration in life. Photo by Xiao-Yong Chen.

FIGURE 4. Region of western Yunnan Province, China, showing six collection sites. Holotype locality of Exostoma dulongensis sp. nov. is indicated by a star (Xiaojiang River).

FIGURE 5. Holotype locality of Exostoma dulongensis sp. nov. in Xiaojiang River. Photo by Xiao-Yong Chen.

FIGURE 6. Ventral views of mouth parts: A. Exostoma ericinum, KIZ 200106090, 80.1 mm SL; B. Exostoma gaoligongense, KIZ 20040425005, 63.5 mm SL; C. Exostoma dulongensis sp. nov., holotype, KIZ 20040010, 91.7 mm SL; D. Exostoma vinciguerrae, SEABRI 20150389, 74.8 mm SL; E. Exostoma chaudhurii, SEABRI 20150390, 76.9 mm SL.