Glyptothorax prashadi Mukerji, 1932

Ng, Heok Hee & Kottelat, Maurice, 2016, The Glyptothorax of Sundaland: a revisionary study (Teleostei: Sisoridae), Zootaxa 4188 (1), pp. 1-92 : 67-73

Glyptothorax prashadi Mukerji, 1932

( Figs. 33 , 34 )

Glyptothorax prashadi Mukerji, 1932: 281 , Fig. 1 (type locality: Kyenchaung River, Mergui district, Myanmar); Menon, 1954: 42 (in part); Menon & Yazdani, 1968: 129.

Material examined. MYANMAR: ZSI F11334/1 (holotype), 50.4 mm SL; Thanintharyi: Kyenchaung [=Kyein Chaung] River. CMK 25369 (1), 50.7 mm SL ; Tanintharyi: Chaung Ywar Thar Yar (stream) at Ywar Thar Yar (village), about 21 miles south of Chaung La Mu (village), about 15 miles north of Lenya , 11°41'12"N 99°3'56"E. THAILAND: CMK 22046 (4), 22.8–53.8 mm SL ; Ranong: small stream about 5 km N of Kapoe , 9°37'30"N 98°36'26"E. CMK 22010 (2), 48.4–50.3 mm SL ; Ranong: Khlong Chakhli at bridge about 1.5 km S of Ban Bang Hin, 9°30’59”N 98°32’53”E. CMK 22027 (1), 45.4 mm SL ; Ranong: Khlong Chakhli at end of road about 3 km S of Ban Bang Hin, 9°30’25”N 98°33’7”E.

Diagnosis. Glyptothorax prashadi differs from all Sundaic congeners except G. f u s cu s and G. s t i b a ro s in having a straight (vs. concave) margin of the dorsal fin. It is distinguished from both G. f u s cu s and G. stibaros in having a less tapering body, as manifested by the smaller ratio between the body and caudal peduncle depths (caudal peduncle depth 1.8–1.9 times in body depth at dorsal-fin origin vs. 2.3–3.8). Glyptothorax prashadi further differs from G. f u s c u s in having an broadly (vs. acutely) rounded snout when viewed dorsally ( Fig. 13 ), expanded distal tips of neural spines not forming (vs. forming) a series of low bumps anterior to adipose fin and a caudal fin with pointed (vs acutely rounded) lobes and uniform color pattern without hyaline areas (vs. with hyaline areas in the median fin rays and tips of fin lobes; Fig. 14 ), and from G. stibaros in having a smooth (vs. serrated) posterior margin of the dorsal-fin spine and a longer, deeper caudal peduncle (length 20.1–22.2% SL vs. 16.0–19.7; depth 8.3–10.3% SL vs. 6.9–8.2). The following unique combination of characters further distinguishes G. prashadi from Sundaic congeners: head width 18.3–23.3% SL; anteromedial striae in thoracic adhesive apparatus absent; dorsalto-adipose distance 14.8–20.6% SL; body depth at anus 15.6–20.7% SL; straight dorsoposterior margin of adipose fin; post-adipose distance 15.7–20.8% SL; preanal length 61.9–64.7% SL; caudal peduncle depth 7.4–10.9% SL; caudal-fin length 28.7–33.9% SL; dark bands on caudal-fin lobes running divergent to longitudinal axis of lobes; lacking both prominent pale midlateral stripes on the body and dark vertical bars at adipose-fin base and caudal-fin base.

Description. Morphometric data in Table 14 . Head depressed; body subcylindrical. Dorsal profile rising steeply 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 on sides of body generally larger than those on dorsal surfaces of head and body. Lateral line complete and midlateral. Vertebrae 17+18=35 (2) or 17+19=36 (2).

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+7 (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 half) 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 ovate field extending from isthmus to just beyond posterior limit of pectoral-fin base ( Fig. 3 n). Narrow, lanceolate medial pit on posterior third. Striae uninterrupted and radiating from median depression anteriorly. Striae at posterior end of apparatus broken up into small rounded plaques in specimens from the Tenasserim River drainage, but not in those from the Kapoe River drainage ( Fig. 35 ).

Dorsal fin located above anterior third of body, with I,5,i (5) rays; fin margin straight; 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,7,8,i (5) 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 iii,8 (1), iv,7,i (1), iii,8,i (1) or iv,8 (2) rays. Pelvic-fin origin at vertical through posterior limit of dorsal-fin base. Pelvic fin with slightly convex margin and i,5 (5) rays; tip of adpressed fin not reaching anal-fin origin. Pectoral fin with I,6 (1), I,6,i (2), I,7 (1) or I,7,i (1) rays; posterior fin margin slightly concave; anterior spine margin smooth, posterior margin with 4–7 serrations.

Coloration. In 70% ethanol: dorsal and lateral surfaces of head and body brown to gray, fading to paler color (beige to light gray) on ventral surfaces. Dorsal and lateral surfaces of head and body with small irregular darker spots. A thin, pale (usually cream) mid-dorsal stripe extending from base of last dorsal-fin ray to origin of adipose fin; stripe indistinct or nearly 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 brown or gray fin rays, with more diffuselycolored fin membranes. Adipose fin brown or gray, with more diffsely-colored distal margin. Caudal fin uniformly mottled brown or gray, without hyaline areas. Maxillary and nasal barbels brown to gray dorsally, beige ventrally. Mandibular barbels beige.

Distribution. Glyptothorax prashadi is found in the eastern half of the northern Malay Peninsula (from the Tenasserim River drainage southwards to the Kapoe River drainage ( Fig. 36 ).

Habitat and biology. Glyptothorax prashadi is typically found in lower elevation hillstreams and streams draining the foothills throughout its range. Such streams typically have a moderate to swift current, a mixed sand/ gravel bottom and thick vegetation on the banks.

Comparisons. Besides G. f u s c u s (which has already been compared with G. prashadi in the diagnosis), there are seven congeners known from the Malay Peninsula and Sumatra: G. amnestus , G. famelicus , G. k e l u k, G. ketambe , G. platypogonides , G. plectilis and G. schmidti . Glyptothorax prashadi further differs from G. famelicus , G. ketambe and G. schmidti in lacking (vs. with) prominent pale midlateral stripes on the body, and in having a deeper body (depth at anus 15.8–18.8% SL vs. 11.4–15.7); it further differs from G. famelicus in having a wider head (20.2–22.8% SL vs. 16.7–20.0) and a deeper caudal peduncle (8.3–10.3% SL vs. 5.8–7.3). Glyptothorax prashadi is further distinguished from G. keluk in having a deeper body (depth at anus 15.8–18.8% SL vs. 14.0– 15.8) and a straight (vs. convex) dorsoposterior margin of the adipose fin, and from G. ketambe in having a wider head (20.2–22.8% SL vs. 16.1–17.9). It further differs from G. platypogonides in having a wider head (20.2–22.8% SL vs. 17.0–20.5), a deeper body (depth at anus 15.8–18.8% SL vs. 12.1–14.8) and a deeper caudal peduncle (8.3– 10.3% SL vs. 6.5–7.9), and from G. plectilis in lacking (vs. having) anteromedial striae in the thoracic adhesive apparatus and having a longer caudal peduncle (20.1–22.2% SL vs. 13.4–19.9). Among congeners known only from Borneo, it further differs from G. decussatus in lacking (vs. having) anteromedial striae in the thoracic adhesive apparatus, having a shorter post-adipose distance (17.9–20.8% SL vs. 16.2–17.5), a more slender caudal peduncle (8.3–10.3% SL vs. 10.3–10.9), from G. exodon in having the premaxillary toothband approximately half (vs. almost entirely) exposed when the mouth is closed, a wider head (20.2–22.8% SL vs. 16.0–18.1), a shorter dorsal-to-adipose distance (15.2–19.8% SL vs. 21.9–26.3), a shorter post-adipose distance (17.9–28.8% SL vs. 21.5–24.0), a deeper body (depth at anus 15.8–18.8% SL vs. 13.8–15.8), and a deeper caudal peduncle (8.3–10.3% SL vs. 6.8–7.3), and from G. m a j o r in lacking (vs. having) anteromedial striae in the thoracic adhesive apparatus and a longer caudal peduncle (20.1–22.2% SL vs. 14.2–19.8). Glyptothorax prashadi is further distinguished from G. nieuwenhuisi in having a deeper caudal peduncle (8.3–10.3% SL vs. 7.0–8.4), and from G. pictus in lacking (vs. having) dark vertical bars at adipose-fin base and caudal-fin base. Among congeners known only from Java, G. prashadi further differs from G. platypogon in having a shorter preanal length (61.9–64.7% SL vs. 65.7–72.3), a straight (vs. convex) dorsoposterior margin of the adipose fin, a longer post-adipose distance (17.9–20.8% SL vs. 14.6–17.6), a longer caudal peduncle (20.1–22.2% SL vs. 15.5–18.2) and a longer caudal fin (28.3–34.8% SL vs. 20.1–27.0), and from G. robustus in having (vs. lacking) a medial pit in the thoracic adhesive apparatus, broader striae on the thoracic adhesive apparatus (compare Figs. 3 e and 3n), a wider head (20.2–22.8% SL vs. 17.6–20.3), a deeper caudal peduncle (8.3–10.3% SL vs. 6.6–8.3) and lacking (vs. having) prominent dark longitudinal stripes running through each caudal fin lobe.

Remarks. The thoracic adhesive apparatus of G. prashadi specimens we have examined from the northern end of its distribution (Tenasserim River drainage) have the striae broken up into smaller, rounded plaques posteriorly ( Fig. 35 a); this feature is not seen in specimens from the southern end of its distribution (Kapoe River drainage; Fig. 35 b). This precludes us from using this character to diagnose G. prashadi from congeners (most notably G. fuscus , which has the striae of the thoracic adhesive apparatus intact posteriorly).

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 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 13. Dorsal views of heads of: a. Glyptothorax fuscus, ZRC 38732, 52.1 mm SL; b. G. prashadi, CMK 25369, 50.7 mm

FIGURE 14. Lateral views of caudal region of: a. Glyptothorax fuscus, ZRC 38732, 51.5 mm SL; b. G. prashadi, CMK 25369, 50.7 mm SL. Illustrations not to scale.

FIGURE 33. Glyptothorax prashadi, ZSI F 11334 / 1, holotype, 50.4 mm SL; Myanmar: Kyenchaung River. Dorsal, lateral and ventral views.

FIGURE 34. Glyptothorax prashadi, CMK 25369, 50.7 mm SL; Myanmar: Kyenchaung River. Dorsal, lateral and ventral views.

FIGURE 35. Thoracic adhesive apparatus of Glyptothorax prashadi: a. CMK 25369, 50.7 mm SL; Myanmar: Tenasserim River drainage; b. CMK 22046, 53.8 mm SL; Thailand: Kapoe River drainage, showing differences in morphology of striae posteriorly. Striae broken up into round plaques indicated with arrow. Illustrations not to scale.

FIGURE 36. Map showing collection localities of Glyptothorax prashadi, G. schmidti and G. stibaros.

Tables

TABLE 14. Morphometric data for Glyptothorax prashadi (n = 7).

	Range	Mean±SD
Standard length (mm)	28.5–75.9
%SL
Predorsal length	37.7–39.3	38.6±0.52
Preanal length	61.9–64.7	63.2±1.09
Prepelvic length	47.9–51.5	49.6±1.17
Prepectoral length	20.4–23.8	22.4±1.17
Length of dorsal-fin base	12.9–15.6	14.2±1.03
Dorsal-fin spine length	14.2–17.3	15.3±1.34
Length of anal-fin base	15.6–19.6	17.0±1.35
Pelvic-fin length	13.8–15.1	14.4±0.44
Pectoral-fin length	20.4–26.0	23.3±1.86
Pectoral-fin spine length	15.7–21.1	18.4±2.01
Caudal-fin length	28.3–34.8	31.3±2.32
Length of adipose-fin base	12.8–18.9	16.0±2.18
Dorsal to adipose distance	15.2–19.8	17.8±1.67
Post-adipose distance	17.9–20.8	19.8±1.04
Length of caudal peduncle	20.1–22.2	21.3±0.82
Depth of caudal peduncle	8.3–10.3	9.6±0.67
Body depth at anus	15.8–18.8	17.0±1.20
Body depth at dorsal-fin origin	20.4–23.5	22.0±1.33
Head length	26.2–29.8	28.8±1.29
Head width	20.2–22.8	21.3±0.83
Head depth	15.2–18.4	16.6±1.02
%HL
Snout length	45–52	49±2.2
Interorbital distance	27–30	28±0.9
Eye diameter	7–11	10±1.2
Nasal barbel length	15–23	19±2.8
Maxillary barbel length	70–92	81±7.6
Inner mandibular barbel length	29–41	36±4.4
Outer mandibular barbel length	49–59	54±4.2