Glyptothorax keluk, Ng, Heok Hee & Kottelat, Maurice, 2016

Ng, Heok Hee & Kottelat, Maurice, 2016, The Glyptothorax of Sundaland: a revisionary study (Teleostei: Sisoridae), Zootaxa 4188 (1), pp. 1-92 : 32-35

Glyptothorax keluk new species

( Fig. 18 )

Type material. Holotype: MZB 17217, 52.5 mm SL; Sumatra : Sumatera Selatan, Air Lintang , 4°4'20"S 103°19'25"E; L. M. Page et al., 4 August 2006.

Paratypes: UF 166629 (3), 35.5–58.3 mm SL; ZRC 54229 (2), 37.2–41.3 mm SL; data as for holotype .

Diagnosis. Glyptothorax keluk differs from Sundaic congeners except G. platypogon in having a convex (vs. straight) dorsoposterior margin of the adipose fin ( Fig. 7 ). It can be distinguished from G. platypogon in having a longer pectoral-fin spine (19.4–22.9% SL vs. 13.6–17.9) and a longer caudal fin (26.9–30.7% SL vs. 20.1–27.0). The following unique combination of characters further distinguishes G. keluk from Sundaic congeners: eye diameter 7–11% HL; head width 18.8–20.4% SL; anteromedial striae in thoracic adhesive apparatus absent; predorsal length 36.4–41.3% SL; dorsal-fin spine length 16.0–20.1% SL; margin of dorsal fin concave; dorsal-toadipose distance 18.4–22.5% SL; body depth at anus 14.0–15.8% SL; adipose-fin base length 13.6–17.2% SL; post-adipose distance 15.2–16.7% SL; caudal peduncle depth 7.7–8.8% SL; premaxillary toothband partially exposed when mouth is closed; anteromedial striae absent in thoracic adhesive apparatus; and uniformly dark body with neither contrasting markings nor prominent pale midlateral stripe.

Description. Morphometric data in Table 6 . Head depressed; body slender, 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 tuberculate, with tubercles of even size on sides of body. Lateral line complete and midlateral. Vertebrae 17+18=35* (1), 18+17=35 (2) or 18+18=36 (1).

Head depressed and broad, triangular when viewed laterally. Snout prominent. Anterior and posterior nares large and separated only by base of nasal barbel. Gill opening broad, extending from ventral margin of posttemporal to isthmus. First branchial arch with 2+6* (3), 2+7 (2), 2+8 (1) or 2+9 (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 midway between its base and that of pectoral spine. Outer mandibular barbel extending to two-thirds of distance between its base and that of pectoral spine.

Mouth inferior, premaxillary tooth band partially (approximately two-thirds) exposed when mouth is closed. Oral teeth small and villiform, in irregular rows on all tooth-bearing surfaces. Premaxillary teeth appearing 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 elongate ovate field extending from isthmus to just beyond posterior limit of pectoral-fin base ( Fig. 3 f). Anteromedial striae absent. Narrow, v-shaped medial pit on posterior half.

Dorsal fin located above anterior third of body, with I,6 (6) rays; fin margin concave; spine short and straight, smooth on anterior and posterior margins. Adipose fin with anterior margin straight or slightly concave and posterior margin convex. Caudal fin strongly forked, with lower lobe slightly longer than upper lobe and i,7,8,i (6) principal rays. Procurrent rays symmetrical and extending only slightly anterior to fin base. Anal-fin base vertically opposite adipose-fin base. Anal fin with straight anterior margin and straight or slightly concave posterior margin; with iv,7,1 (1), iv,8 (2) or iv,8,i* (3) rays. Pelvic-fin origin at vertical through posterior limit of dorsal-fin base. Pelvic fin with slightly convex margin and i,5 (6) rays; tip of adpressed fin not reaching anal-fin origin. Pectoral fin with I,7,i* (3), I,8 (2) or I,8,i (1) rays; posterior fin margin slightly concave; anterior spine margin smooth, posterior margin with 7–9 (holotype =8) serrations.

Coloration. In 70% ethanol: dorsal and lateral surfaces of head and body dark brownish gray, fading to light gray or beige on ventral surfaces. A thin, light brown mid-dorsal stripe extending from base of last dorsal-fin ray to origin of adipose fin; stripe absent in 2 of 6 individuals examined. Laterosensory pores rimmed in beige, imparting appearance of a diffuse light brown or light gray midlateral line. Dorsal and ventral surfaces of caudal peduncle slightly paler in 2 of 6 individuals examined. All fins with rays proximally gray to grayish brown, becoming hyaline more distally, and diffuse melanophores on fin membranes. Pectoral and pelvic fins with gray or grayish brown on base of fin rays and hyaline posterior margin. Anal fin with gray or grayish brown base; gray or grayish brown spot on anterior third of fin present in 3 of 6 individuals examined. Adipose fin gray or grayish brown with hyaline distal margin. Base of caudal fin with dark crescent in 5 of 6 individuals examined. Each caudal-fin lobe with irregular, elongate gray or grayish brown blotch on about half of outer fin rays; most of inner rays of lobes hyaline. Maxillary and nasal barbels gray or grayish brown dorsally, light brown or light gray ventrally. Mandibular barbels beige or light gray.

Distribution. Glyptothorax keluk is known only from the Musi River drainage in southern Sumatra ( Fig. 19 ).

Etymology. The specific epithet comes from the Malay keluk , meaning curve, and is used as a noun in apposition in reference to the convex dorsoposterior margin of the adipose fin.

Comparisons. Glyptothorax keluk superficially resembles G. amnestus in having a uniformly dark body, but can be additionally distinguished from it in lacking (vs. having) anteromedial striae in the thoracic adhesive apparatus and having a more slender snout when viewed dorsally ( Fig. 6 ) and a more slender caudal peduncle (7.7– 8.8% SL vs. 9.8–11.2). There are six other congeners known from Sumatra: G. famelicus , G. fuscus , G. ketambe , G. platypogonides , G. plectilis and G. schmidti . Glyptothorax keluk further differs from G. famelicus and G. ke t a m b e in lacking (vs. having) a prominent pale midlateral stripe on the body, a greater predorsal length (36.4–41.3% SL vs. 32.1–35.9), a longer dorsal-fin spine (16.0–20.1% SL vs. 8.9–14.8), a longer pectoral-fin spine (19.4–22.9% SL vs. 14.0–16.6) and a shorter post-adipose distance (15.2–16.7% SL vs. 19.1–22.0), and from G. f u s cu s in having a concave (vs. straight) margin of the dorsal fin and a more slender body (depth at anus 14.0–15.8% SL vs. 15.6– 20.7). It is further distinguished from G. plectilis in lacking (vs. having) anteromedial striae in the thoracic adhesive apparatus, from G. platypogonides in having a uniform (vs. mottled) coloration, a smaller eye (diameter 7–11% HL vs. 11–14), a longer adipose-fin base (13.6–17.2% SL vs. 10.7–13.7) and a shorter post-adipose distance (15.2– 16.7% SL vs. 17.6–21.5), and from G. schmidti in lacking (vs. having) a prominent pale midlateral stripe on the body, having a longer dorsal-fin spine (16.0–20.1% SL vs. 8.9–14.9), a shorter dorsal-to-adipose distance (18.4– 22.5% SL vs. 23.9–28.1) and a shorter post-adipose distance (15.2–16.7% SL vs. 18.9–22.0).

Among the remaining Sundaic congeners, G. k el u k further differs from G. decussatus in lacking (vs. having) anteromedial striae in the thoracic adhesive apparatus, having a more slender body (depth at anus 14.0–15.8% SL vs. 17.8–19.7) and a more slender caudal peduncle (depth 7.7–8.8% SL vs. 10.3–10.9), from G. exodon in having the premaxillary toothband approximately two-thirds (vs. almost entirely) exposed when the mouth is closed, a wider head (18.8–20.4% SL vs. 16.0–18.1), a shorter post-adipose distance (15.2–16.7% SL vs. 21.5–24.0) and a deeper caudal peduncle (7.7–8.8% SL vs. 6.8–7.3), and from G. major in lacking (vs. having) anteromedial striae in the thoracic adhesive apparatus. It is further distinguished from G. nieuwenhuisi in lacking (vs. having) dark spots on the body, from G. pictus in having a uniformly dark body without contrasting markings (vs. paler body with dark vertical bars at adipose-fin base and caudal-fin base), and from G. prashadi in having a concave (vs. straight) margin of the dorsal fin, a more slender body (depth at anus 14.0–15.8% SL vs. 15.8–18.8). Glyptothorax keluk further differs from G. robustus in having (vs. lacking) a medial pit in the thoracic adhesive apparatus, a longer pectoral-fin spine (19.4–22.9% SL vs. 16.8–19.6) and a shorter post-adipose distance (15.2–16.7% SL vs. 17.0– 19.6), and from G. stibaros in having a smooth (vs. serrated) posterior margin of the dorsal-fin spine and a more slender body (depth at anus 14.0–15.8% SL vs. 15.6–20.6).

Figures

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 6. Dorsal views of head of: a. Glyptothorax amnestus, ZRC 38708, 54.1 mm SL; b. G. keluk, MZB 17217, holotype, 52.5 mm SL. Illustrations not to scale.

FIGURE 7. Lateral views of caudal region of: a. Glyptothorax amnestus, ZRC 38708, 54.1 mm SL; b. G. keluk, MZB 17217, holotype, 52.5 mm SL. Illustrations not to scale.

FIGURE 18. Glyptothorax keluk, MZB 17217, holotype, 52.5 mm SL; Sumatra: Sumatera Selatan, Air Lintang. Dorsal, lateral and ventral views.

FIGURE 19. Map showing collection localities of Glyptothorax keluk, G. ketambe and G. major.

Tables

TABLE 6. Morphometric data for Glyptothorax keluk (n = 6).

	Holotype MZB 17217	Range	Mean±SD
Standard length (mm) %SL	52.5	35.5–58.3
Predorsal length Preanal length Prepelvic length	41.3 66.3 51.8	36.4–41.3 64.6–68.8 48.0–52.4	38.3±1.90 66.6±1.51 50.7±1.74
Prepectoral length Length of dorsal-fin base Dorsal-fin spine length	22.1 15.0 18.7	21.2–24.7 13.0–15.0 16.0–20.1	22.8±1.37 13.9±0.79 18.1±1.50
Length of anal-fin base Pelvic-fin length Pectoral-fin length	15.4 15.0	14.4–17.7 13.2–15.8 22.0–27.5	15.6±1.26 14.9±1.02 23.8±2.53
Pectoral-fin spine length Caudal-fin length Length of adipose-fin base	22.9 30.7 16.8	19.4–22.9 26.9–30.7 13.6–17.2	21.0±1.79 29.2±1.45 15.9±1.44
Dorsal to adipose distance Post-adipose distance Length of caudal peduncle	22.5 16.4 18.5	18.4–22.5 15.2–16.7 17.6–19.6	20.9±2.13 16.1±0.68 18.5±0.73
Depth of caudal peduncle Body depth at anus Body depth at dorsal-fin origin	8.4 15.0 20.8	7.7–8.8 14.0–15.8 18.2–20.8	8.3±0.45 15.0±0.71 19.4±1.30
Head length Head width Head depth	30.5 20.4 15.4	26.6–30.5 18.8–20.4 13.9–18.2	28.6±1.53 19.7±0.58 15.5±1.62
%HL Snout length Interorbital distance	51 24	45–52 24–31	49±3.0 27±2.6
Eye diameter Nasal barbel length Maxillary barbel length	9 24 84	7–11 21–30 79–99	10±1.6 25±4.0 89±7.8
Inner mandibular barbel length Outer mandibular barbel length	35 49	30–36 43–54	33±2.4 48±4.3