Glyptothorax plectilis Ng & Hadiaty, 2008

Ng, Heok Hee & Kottelat, Maurice, 2016, The Glyptothorax of Sundaland: a revisionary study (Teleostei: Sisoridae), Zootaxa 4188 (1), pp. 1-92 : 64-67

Glyptothorax plectilis Ng & Hadiaty, 2008

( Fig. 32 )

Glyptothorax plectilis Ng & Hadiaty, 2008: 138 , Figs. 1–2 A (type locality: Sungai Ketambe , a tributary of Sungai Alas, 3°41'N 97°39'E, Nangroe Aceh Darussalam, Sumatra).

Glyptothorax major (non Boulenger, 1894)— Wirjoatmodjo 1987: 244.

Material examined. SUMATRA: MZB 8702 (holotype), 75.9 mm SL ; MZB 8693 (1 paratype), 62.4 mm SL; MZB 8699 (2 paratypes), 28.5–37.4 mm SL; MZB 8700 (1 paratype), 45.7 mm SL; MZB 8702 (2 paratypes), 62.4–75.9 mm SL; Nangroe Aceh Darussalam: Sungai Ketambe , a tributary of Sungai Alas , 3°41'N, 97°39'E. MZB 4530 (1 paratype), 50.2 mm SL ; Nangroe Aceh Darussalam: Ketambe , Gurah, Sungai Alas , 3°45'N 97°9'E. MZB 8698 (2 paratypes), 42.6–68.0 mm SL ; ZRC 46420 (1 paratype), 44.3 mm SL; Nangroe Aceh Darussalam: Ketambe , Sungai Alas in front of Forestry Department guest house, 3°40'N, 97°30'E. MZB 8701 (4 paratypes), 38.8–53.1 mm SL ; Nangroe Aceh Darussalam: Sungai Alas at Aunan village , 3°40'N, 97°30'E. MZB 8696 (18 paratypes), 40.7–50.9 mm SL ; USNM 389642 (11), 44.6–68.9 mm SL; Nangroe Aceh Darussalam: Kutacane fish market, 3°30'N, 97°48'E. USNM 390038 (2), 35.8–57.4 mm SL ; Nanggroe Aceh Darussalam: Sungai Lae Petal on road from Subulussalam to Singkil , 2°31'45.5"N 98°2'38.3"E. USNM 390072 (2), 13.0– 62.6 mm SL ; Sumatera Utara : Kabupaten Tapanuli Utara, Kecamatan Adian Koting, Desa Pangsikaman, Aek Raisan (river) at Sibolga– Tarutung road, 1°50'6.7"N 98°49'48.9"E.

Diagnosis. Glyptothorax plectilis can be distinguished from Sundaland congeners except G. amnestus , G. decussatus and G. major in having (vs. lacking) anteromedial striae in the thoracic adhesive apparatus. It differs from all three species in having prominent, enlarged tubercles (vs. with small tubercles of uniform size) along the flanks. Glyptothorax plectilis is additionally distinguished from G. amnestus in having an ovate thoracic adhesive apparatus with gently convex lateral edges (vs. oblong with almost straight lateral edges; compare Figs. 3 a and 3m) and from G. major in having the anterolateral edges of the thoracic adhesive apparatus gently convex (vs. markedly concave; compare Figs. 3 h and 3m) and a smaller head (25.3–27.9% SL vs. 27.2–31.3). The following unique combination of characters further distinguishes G. plectilis from Sundaic congeners: premaxillary toothband approximately two-thirds exposed when mouth is closed; head width 18.4–23.5% SL; head depth 15.2–19.4% SL; predorsal length 35.3–40.6% SL; margin of dorsal fin concave; dorsal-to-adipose distance 17.9–23.5% SL; adipose-fin base length 12.9–17.2% SL; straight dorsoposterior margin of adipose fin; caudal peduncle depth 8.4– 10.6% SL; caudal peduncle length 13.4–19.9% SL; post-adipose distance 14.0–17.6% SL; caudal fin length 26.6– 33.1% SL; and body with dark spots but without dark vertical bars or distinct midlateral pale stripes.

Description. Morphometric data in Table 13 . Head depressed; body robust, 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 18+16=34 (2), 17+18=35 (2), 18+17=35 (7) or 19+17=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 1+8 (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 almost posterior limit of pectoral-fin base ( Fig. 3 m). Anteromedial striae present. Narrow, v-shaped medial pit on posterior half.

Dorsal fin located above anterior third of body, with I,6 (8) 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 straight. Caudal fin strongly forked, with lower lobe slightly longer than upper lobe and i,7,7,i (1) or i,7,8,i* (7) 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,8* (6) or iv,9 (2) rays. Pelvic-fin origin at vertical through posterior limit of dorsal-fin base. Pelvic fin with slightly convex margin and i,5 (8) rays; tip of adpressed fin not reaching anal-fin origin. Pectoral fin with I,8 (8) rays; posterior fin margin slightly concave; anterior spine margin smooth, posterior margin with 7–11 (holotype =11) serrations.

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

Distribution. Glyptothorax plectilis is known from the Alas River drainage and the Aek Kolang drainage along the western coast of northern Sumatra ( Fig. 26 ). It is expected to occur in intermediate drainages and probably other rivers draining to the Indian Ocean.

Habitat and biology. Glyptothorax plectilis has been collected from streams with flowing, clear water and a substrate of sand, gravel and large rocks. It is apparently spawning twice a year: once in March/April and again in September/October ( Wirjoatmodjo, 1987). The main diet is insect larvae of the genera Simulium, Hydropsyche and Acroneuria ( Rachmatika & Wirjoatmodjo, 1988) .

Comparisons. Besides G. amnestus , whose differences with G. plectilis are already outlined in the diagnosis, there are six other congeners known from Sumatra: G. famelicus , G. f u s c u s, G. keluk , G. ketambe , G. platypogonides and G. s c h m i d t i. Glyptothorax plectilis is further distinguished from G. famelicus , G. platypogonides and G. schmidti in having a deeper body (depth at anus 15.3–18.8% SL vs. 11.4–15.7), a deeper caudal peduncle (8.4– 10.6% SL vs. 5.8–8.7) and a shorter post-adipose distance (14.0–17.6% SL vs. 17.6–22.0), from G. famelicus in having a greater predorsal length (35.3–40.6% SL vs. 32.1–35.2) and a longer adipose-fin base (12.9–17.2% SL vs. 11.4–12.8), and from G. f u s c u s in having a concave (vs. straight) margin of the dorsal fin. It further differs from G. keluk in having a straight (vs. convex) dorsoposterior margin of the adipose fin, from G. ketambe in having a wider head (18.4–23.5% SL vs. 16.1–17.9), a deeper body (depth at anus 15.3–18.8% SL vs. 12.7–15.3) and a shorter caudal peduncle (13.4–19.9% SL vs. 20.1–22.9), and from G. schmidti in having a shorter dorsal-to-adipose distance (17.9–23.5% SL vs. 23.9–28.1), and lacking (vs. having) a prominent pale midlateral stripe on the body.

Among the remaining Sundaic congeners, G. plectilis further differs from G. exodon in having the premaxillary tooth band approximately two-thirds (vs. almost entirely) exposed when the mouth is closed, a wider (18.4–23.5% SL vs. 16.0–18.1) and deeper (15.2–19.4% SL vs. 13.8–15.1) head, and a shorter post-adipose distance (14.0– 17.6% SL vs. 21.5–24.0), from G. nieuwenhuisi in having a deeper caudal peduncle (8.4–10.6% SL vs. 7.0–8.4), and from G. p i ct u s in lacking (vs. having) dark vertical bars at the adipose-fin base and the base of the caudal fin. It is further distinguished from G. platypogon in having a straight (vs. convex) dorsoposterior margin of the adipose fin, a longer caudal fin (26.6–33.1% SL vs. 20.1–27.0) and the presence (vs. absence) of dark spots on the body, and from G. prashadi in having a concave (vs. straight) margin of the dorsal fin and a shorter caudal peduncle (13.4–19.9% SL vs. 20.1–22.2). Glyptothorax plectilis can be further differentiated from both G. robustus and G. stibaros in having a deeper caudal peduncle (8.4–10.6% SL vs. 6.6–8.3), 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,

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 26. Map showing collection localities of Glyptothorax pictus, G. plectilis and G. robustus.

FIGURE 32. Glyptothorax plectilis, USNM 390072, 62.6 mm SL; Sumatra: Sumatera Utara: Aek Raisan. Dorsal, lateral and ventral views.

Tables

TABLE 13. Morphometric data for Glyptothorax plectilis (n = 16).

	Range	Mean±SD
Standard length (mm)	28.5–75.9
%SL
Predorsal length	35.3–40.6	38.1±1.56
Preanal length	65.0–72.2	68.3±1.95
Prepelvic length	48.3–56.8	52.2±2.23
Prepectoral length	20.4–26.5	23.4±1.43
Length of dorsal-fin base	12.1–15.6	13.7±0.98
Dorsal-fin spine length	13.1–20.1	16.7±1.95
Length of anal-fin base	14.9–21.2	17.7±2.52
Pelvic-fin length	15.1–18.3	16.3±0.89
Pectoral-fin length	22.3–27.5	25.1±1.61
Pectoral-fin spine length	15.0–21.4	19.2±1.99
Caudal-fin length	26.6–33.1	29.0±1.94
Length of adipose-fin base	12.9–17.2	15.0±1.37
Dorsal to adipose distance	17.9–23.5	21.2±1.46
Post-adipose distance	14.0–17.6	16.1±1.02
Length of caudal peduncle	13.4–19.9	17.4±1.59
Depth of caudal peduncle	8.4–10.6	9.4±0.369
Body depth at anus	15.3–18.8	16.8±1.01
Body depth at dorsal-fin origin	18.5–22.6	20.4±1.61
Head length	25.3–27.9	26.7±0.91
Head width	18.4–23.5	21.1±1.42
Head depth	15.2–19.4	17.1±1.20
%HL
Snout length	45–54	30±2.3
Interorbital distance	26–33	29±2.1
Eye diameter	8–13	11±1.5
Nasal barbel length	17–27	23±3.0
Maxillary barbel length	79–120	97±10.5
Inner mandibular barbel length	26–51	37—6.8
Outer mandibular barbel length	45–67	52±5.9