Glyptothorax exodon Ng & Rachmatika 2005

Ng, Heok Hee & Kottelat, Maurice, 2016, The Glyptothorax of Sundaland: a revisionary study (Teleostei: Sisoridae), Zootaxa 4188 (1), pp. 1-92 : 17-20

Glyptothorax exodon Ng & Rachmatika 2005

( Fig. 10 )

Glyptothorax exodon Ng & Rachmatika, 2005: 251 , Figs. 1 , 2 (type locality: Sungai Tekelan, Kalimantan Barat, Borneo) Bagarius bagarius (non Hamilton, 1822) Vaillant, 1902: 72.

Glyptothorax platypogonoides (non Bleeker, 1855)—Roberts, 1989: 136, Fig. 104 lower (in part). Glyptothorax cf. platypogonoides —Ng & Rachmatika, 1999: 182, Fig. 8 B

Material examined. BORNEO: KALIMANTAN BARAT: MZB 9940 (holotype), 57.5 mm SL; Sungai Tekelan, Kapuas River drainage . BMNH 1982.3.29.190 (1 paratype), 63.2 mm SL; CAS 49419 (1 paratype), 59.0 mm SL; RMNH 28907 (1 paratype), 57.2 mm SL; mainstream of Sungai Pinoh, 20–60 km upstream from Nangapinoh, Kapuas River drainage . RMNH 7845 (1 paratype), 60.2 mm SL; Nanga Raun, Kapuas River drainage . MZB 9412 (2 paratypes), 55.1–60.0 mm SL; Sungai Jaket, Embaloh, Kapuas River drainage . MZB 9204 (1), 42.9 mm SL; Sungai Embaloh, Kapuas River drainage . MZB 6633 (1), 42.9 mm SL; Sungai Peyang, Kapuas River drainage. CMK 6905 (1), 29.1 mm SL; Sungai Sibau about 2 km upstream of Putussibau , Kapuas River drainage.

Diagnosis. Glyptothorax exodon can be distinguished from Sundaic congeners in having the premaxillary toothband almost entirely (vs. two-thirds or less) exposed when the mouth is closed. The following unique combination of characters further distinguishes G. exodon from Sundaic congeners: eye diameter 10–13% HL; head width 16.0–18.1% SL; head depth 13.8–15.1% SL; anteromedial striae in thoracic adhesive apparatus absent; prepectoral length 20.6–25.4% SL; predorsal length 36.7–39.2% SL; dorsal-fin spine length 15.0–20.0% SL; margin of dorsal fin concave; smooth posterior margin of dorsal-fin spine; dorsal-to-adipose distance 21.9–26.3% SL; body depth at anus 13.8–15.8% SL; prepelvic length 48.6–52.0% SL; post-adipose distance 21.5–24.0% SL; caudal peduncle depth 6.8–7.3% SL; straight dorsoposterior margin of adipose fin; and mottled body pattern lacking prominent pale stripes.

Description. Morphometric data in Table 3 . Head depressed; body subcylindrical. Dorsal profile rising evenly from tip of snout to origin of dorsal fin, then sloping gently ventrally from origin of dorsal fin to end of caudal peduncle. Ventral profile straight to anal-fin base, then sloping gently dorsally from anal-fin base to end of caudal peduncle. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Skin prominently tuberculate, with ovoid tubercles particularly visible on sides of body. Lateral line complete and midlateral. Vertebrae 17+18=35 (1), 17+19=36 (2), 18+18=36 (2) or 18+19=37 (2).

Head depressed and narrow, triangular when viewed laterally and with acute snout margin when viewed from above. Snout prominent. Anterior and posterior nares large and separated only by base of nasal barbel. Gill opening broad, extending from immediately ventral to post-temporal to isthmus. First branchial arch with 2+6 (1) rakers. Bony elements of dorsal surface of head covered with thick, tuberculate skin. Eye ovoid, horizontal axis longest; located entirely in dorsal half of head.

Barbels in four pairs. Maxillary barbel long and slender, extending to middle of pectoral-fin base. Nasal barbel slender, extending to midway between its base and anterior orbital margin. Inner mandibular barbel extending to two-thirds of distance between its base and that of pectoral spine. Outer mandibular barbel extending to base of pectoral spine.

Mouth inferior, premaxillary tooth band almost wholly exposed when mouth is closed. Oral teeth small and villiform, in irregular rows on all tooth-bearing surfaces. Premaxillary teeth in single broad semilunate band. Dentary teeth in a single crescentic band, consisting of two separate halves tightly bound at midline.

Thoracic adhesive apparatus consisting of keratinized striae in an elliptical field ( Fig. 3 c) extending from isthmus to posterior limit of pectoral-fin base. Anteromedial striae absent. Narrow, v-shaped medial pit on posterior half.

Dorsal fin located above anterior third of body, with I,6 (7) rays; fin margin concave; spine short and gently curved. Adipose fin with anterior margin concave and posterior margin straight. Caudal fin strongly forked, with equal upper and lower lobes and i,7,8,i (7) principal rays. Procurrent rays symmetrical and extending only slightly anterior to fin base. Anal-fin base ventral to adipose-fin origin. Anal fin with straight anterior margin and straight or slightly concave posterior margin; with iv,8 (2) or iv,9* (5) rays. Pelvic-fin origin immediately posterior to vertical through posterior end of dorsal-fin base. Pelvic fin with slightly convex margin and i,5 (7) rays; tip of adpressed fin not reaching anal-fin origin. Pectoral fin with I,8 (7) rays; posterior fin margin slightly concave; anterior spine margin smooth, posterior margin with 10–12 serrations.

Coloration. In 70% ethanol: Dorsal and lateral surfaces of head, and body brown to brownish gray, fading to beige on ventral surfaces. A dark, diffuse midlateral stripe running along lateral line; lateral line without such pigmentation in some individuals, causing it to show up as paler stripe within darker stripe. Body with three long, elliptical pale patches: first above lateral line and spanning region between dorsal and adipose fins, second on anterior half of caudal peduncle above lateral line and third on anterior half of caudal peduncle below lateral line. Dorsal fin with brown base and broad subdistal triangular brown mark. Pectoral fin hyaline, with brown melanophores forming a diffuse broad, transverse band subdistally. Pelvic fin hyaline, with faint transverse brown band in middle. Anal fin with brown base and brown melanophores forming V-shaped subdistal mark on anterior half of fin; rest of fin hyaline. Adipose fin brown to brownish gray, with hyaline distal margin. Caudal fin brown to brownish gray, tips and posterior margins of lobes hyaline. Maxillary barbel brown to brownish gray dorsally, beige ventrally.

Habitat. Glyptothorax exodon is found in swift, clear streams with a substrate consisting of gravel, cobbles or large rocks.

Distribution. Known only from the upper reaches of the Kapuas River drainage in western Borneo ( Fig. 5 ). Glyptothorax exodon has been collected from Sungai Pinoh (a southern tributary of the Kapuas River), the headwaters of the northern tributaries in the Bentuang-Karimun National Park, and Putussibau and is expected to occur in other headwater tributaries in the Kapuas River drainage as well.

Comparisons. Besides the exposure of the premaxillary teeth, G. exodon differs from all Sundaic congeners except for G. famelicus , G. nieuwenhuisi , G. platypogonides , G. robustus , G. schmidti and G. stibaros in having a more slender caudal peduncle (6.8–7.3% SL vs. 7.4–11.4). It is further distinguished from G. famelicus and G. schmidti in having a larger eye (diameter 10–13% HL vs. 5.–10) and a mottled body lacking a prominent pale midlateral stripe (vs. a uniform dark brown body with a prominent pale midlateral stripe), from G. nieuwenhuisi in having a narrower head (16.0–18.1% SL vs. 18.5–21.4) and a longer post-adipose distance (21.5–24.0% SL vs. 16.8–19.7), from G. ro b u s t u s and G. s t i b a ro s in having a larger eye (diameter 10–13% HL vs. 7–10), a longer dorsal-to-adipose distance (21.9–26.3% SL vs. 15.1–21.3) and a more contrasting color pattern on the body (compare Figs. 10 , 37 and 39 ), from G. robustus in having (vs. lacking) a medial pit in the thoracic adhesive apparatus, and from G. stibaros in having a smooth (vs. serrated) posterior margin of the dorsal-fin spine.

There are three other congeners known from Borneo besides G. nieuwenhuisi and G. stibaros (which have been compared with G. exodon in the diagnosis and above): G. decussatus , G. major and G. pictus . Glyptothorax exodon further differs from these three species in having a longer post-adipose distance (21.5–24.0% SL vs. 13.6–19.8); it is additionally distinguished from G. decussatus and G. m a j o r in having a larger eye (diameter 10–13% HL vs. 7– 10), narrower head (16.0–18.1% SL vs. 19.6–23.8) and lacking (vs. having) anteromedial striae in the thoracic adhesive apparatus, from G. decussatus in having a longer post-adipose distance (21.5–24.0% SL vs. 16.2–17.5), and from G. pictus in having a longer dorsal-to-adipose distance (21.9–26.3% SL vs. 14.7–24.1).

Among the other Sundaic congeners, G. exodon further differs from G. amnestus in having a larger eye (diameter 10–13% HL vs. 6–10), a narrower head (16.0–18.1% SL vs. 19.9–23.0), a more slender body (depth at anus 13.8–15.8% SL vs. 15.3–20.6) and a longer post-adipose distance (21.5–24.0% SL vs. 15.8–19.7), from G. fuscus in having a narrower head (16.0–18.1% SL vs. 18.3–23.3), a concave (vs. straight) margin of the dorsal fin, a longer dorsal-to-adipose distance (21.9–26.3% SL vs. 14.8–20.6), a longer post-adipose distance (21.5–24.0% SL vs. 15.7–20.8) and a more slender body (depth at anus 13.8–15.8% SL vs. 15.6–20.7), from G. ke l u k in having a narrower head (16.0–18.1% SL vs. 18.8–20.4), a longer post-adipose distance (21.5–24.0% SL vs. 15.2–16.7) and a straight (vs. convex) dorsoposterior margin of the adipose fin, and from G. ke t a m b e in having a larger eye (diameter 10–13% HL vs. 8–10), a longer prepectoral length (20.6–25.4% SL vs. 18.2–20.6), a greater predorsal length (36.7–39.2% SL vs. 33.3–35.9), a greater prepelvic length (48.6–53.0% SL vs. 45.4–47.8), a longer dorsalfin spine (15.0–20.0% SL vs. 12.5–14.8) and a body with a mottled color pattern (vs. uniformly dark with pale middorsal and midlateral stripes). It is further distinguished from G. platypogon in having a larger eye (diameter 10– 13% HL vs. 7–9), a narrower head (16.0–18.1% SL vs. 19.4–22.3), a straight (vs. convex) dorsoposterior margin of the adipose fin, a longer post-adipose distance (21.5–24.0% SL vs. 14.6–17.6), a longer caudal fin (28.0–31.0% SL vs. 20.1–27.0) and a body with a mottled (vs. uniform) color pattern, from G. plectilis in having a narrower (16.0– 18.1% SL vs. 18.4–23.5) and more slender (13.8–15.1% SL vs. 15.2–19.4) head and a longer post-adipose distance (21.5–24.0% SL vs. 14.0–17.6), and from G. prashadi in having a narrower head (16.0–18.1% SL vs. 20.2–22.8), a concave (vs. straight) margin of the dorsal fin and a more slender body (depth at anus 13.8–15.8% SL vs. 15.8– 18.8).

Figures

FIGURE 1. Schematic illustration of thoracic adhesive apparatus of Glyptothorax, showing structures defined and mentioned in this study: anterolateral striae (ALS); anteromedial striae (AMS); medial pit (MP) (based on G. plectilis, MZB 4530, 50.2 mm SL).

FIGURE 2. Glyptothorax amnestus, MZB 17214, holotype, 88.1 mm SL; Sumatra: Padang Panjang. Dorsal, lateral and ventral views.

FIGURE 3. Thoracic adhesive apparatus of: a. Glyptothorax amnestus, ZRC 54231, paratype, 51.2 mm SL; b. G. decussatus, MZB 17216, holotype, 74.5 mm SL; c. G. exodon, BMNH 1982.3. 29.190, paratype, 63.2 mm SL; d. G. famelicus, USNM 193015, holotype, 73.3 mm SL; e. G. f u s c u s, ZRC 42123, 54.3 mm SL; f. G. keluk, MZB 17217, holotype, 52.5 mm SL; g. G. ketambe, MZB 8694, holotype, 100.0 mm SL; h. G. major, ZRC 38761, 59.1 mm SL; i. G. nieuwenhuisi, MZB 16475, 61.0 mm SL; j. G. pictus, MZB 17218, holotype, 54.2 mm SL; k. G. platypogon, ZRC 48376, 56.3 mm SL; l. G. platypogonides, UF 166626, 52.4 mm SL; m. G. plectilis, ZRC 46420, paratype, 44.3 mm SL; n. G. prashadi, CMK 25369, 50.7 mm SL; o. G. robustus, ZRC 48377, 59.9 mm SL; p. G. schmidti, CMK 4536, 74.6 mm SL; q. G. stibaros, MZB 17215, holotype, 55.3 mm SL. Illustrations not to scale.

FIGURE 5. Map showing collection localities of Glyptothorax amnestus, G. decussatus, G. exodon and G. famelicus.

FIGURE 8. Glyptothorax decussatus, MZB 17216, holotype, 74.5 mm SL; Borneo: Kalimantan Timur, En’ggeng B’io. Dorsal, lateral and ventral views.

FIGURE 10. Glyptothorax exodon, BMNH 1982.3. 29.190, paratype, 63.2 mm SL; Borneo: Kalimantan Barat, Sungai Pinoh. Dorsal, lateral and ventral views.

FIGURE 37. Glyptothorax robustus, ZRC 48377, 59.9 mm SL; Java: Jawa Barat, Cisadane River. Dorsal, lateral and ventral views.

FIGURE 39. Glyptothorax stibaros, MZB 17215, holotype, 55.3 mm SL; Borneo: Kalimantan Barat, Sanggau. Dorsal, lateral and ventral views.

Tables

TABLE 3. Morphometric data for Glyptothorax exodon (n = 7).

	Range	Mean±SD
Standard length (mm)	55.1–63.2
%SL
Predorsal length	36.7–39.2	37.9±0.96
Preanal length	64.1–67.8	66.4±1.40
Prepelvic length	48.6–53.0	49.7±1.69
Prepectoral length	20.6–25.4	22.7±2.16
Length of dorsal-fin base	10.6–14.9	12.8±1.43
Dorsal-fin spine length	15.0–20.0	16.7±1.95
Length of anal-fin base	14.2–15.3	14.9±0.46
Pelvic-fin length	15.2–16.5	15.7±0.46
Pectoral-fin length	22.1–25.0	23.7±1.06
Pectoral-fin spine length	16.2–20.3	18.7±1.51
Caudal-fin length	28.0–31.0	29.2±1.02
Length of adipose-fin base	11.0–14.0	13.0±1.13
Dorsal to adipose distance	21.9–26.3	23.4±2.51
Post-adipose distance	21.5–24.0	22.5±1.32
Length of caudal peduncle	18.0–20.6	19.3±1.07
Depth of caudal peduncle	6.8–7.3	7.0±0.21
Body depth at anus	13.8–15.8	14.5±0.88
Body depth at dorsal-fin origin	18.9–20.0	19.6±0.59
Head length	25.7–29.2	26.8±1.28
Head width	16.0–18.1	17.0±0.85
Head depth	13.8–15.1	14.3±0.56
%HL
Snout length	44–47	46±1.0
Interorbital distance	24–27	25±1.2
Eye diameter	10–13	12±1.0
Nasal barbel length	15–20	18±2.1
Maxillary barbel length	92–111	99±9.3
Inner mandibular barbel length	30–39	34±4.5
Outer mandibular barbel length	48–67	55±8.1