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420
Accepted by R. Pethiyagoda: 15 Sept. 2014; published: 2 Oct. 2014
ZOOTAXA
ISSN 1175-5326 (print edition)
ISSN
1175-5334
(online edition)
Copyright © 2014 Magnolia Press
Zootaxa 3869 (4): 420
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434
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Article
http://dx.doi.org/10.11646/zootaxa.3869.4.6
http://zoobank.org/urn:lsid:zoobank.org:pub:39555505-B707-4172-BED0-06242CB096EC
A review of the glyptosternine catfish genus Exostoma Blyth 1860 from Thailand,
with descriptions of two new species (Teleostei: Siluriformes)
HEOK HEE NG
1
& CHAVALIT VIDTHAYANON
2
1
c/o Lee Kong Chian Natural History Museum, 6 Science Drive 2, #03-01, Singapore 117546. E-mail: heokhee.ng@gmail.com
2
Mekong River Commission, 184 Fa Ngum Road, Unit 18 Ban Sithan Neua, Vientiane 01000, Lao PDR.
E-mail: chavalit@mrcmekong.org
Abstract
We review members of the sisorid catfish genus Exostoma known from Thailand. Three species are recognized, of which
two from the headwaters of the Chao Phraya River drainage in northwestern Thailand, are described here as new: E. ef-
frenum and E. peregrinator. In addition to the two new species, E. berdmorei (which is here redescribed) is also known
from the Salween River drainage in western Thailand. The three species can be distinguished from each other and other
congeners by the morphologies of the adipose and caudal fins, as well as morphometric data for the eye diameter, head
width, dorsal-to-adipose distance, body depth at anus, caudal-peduncle length, caudal-peduncle depth, and numbers of
branched pectoral-fin rays and preanal vertebrae.
Key words: Sisoridae, Glyptosternini, Salween River, Chao Phraya River
Introduction
Glyptosternines are sisorid catfishes with distinctively depressed heads and bodies and greatly-enlarged paired fins
modified to form an adhesive apparatus. Known from torrential streams and rivers from the upper reaches of the
Amu Darya River drainage in Turkmenistan southwards to the Mekong River drainage in Indochina and eastwards
to the Yangtze River (Changjiang) drainage in central China, glyptosternines have been shown to be a
monophyletic group (de Pinna, 1996; Peng et al., 2004; Guo et al., 2005).
The glyptosternine catfish genus Exostoma currently consists of five species known from the Brahmaputra,
Irrawaddy and Salween river drainages in China, India and Myanmar (Thomson & Page, 2006; Vishwanath &
Joyshree, 2007). Members of the genus are diagnosed from other glyptosternines by a combination of: continuous
post-labial groove; gill openings not extending onto venter; homodont dentition; oar-shaped, distally flattened teeth
in both jaws; tooth patches separated in upper jaw; 10–11 branched pectoral rays (Thomson & Page, 2006).
The distribution of the genus reaches its easternmost limit in Thailand, where populations collected from the
Chao Phraya and Salween River drainages appear morphologically distinct and seem to represent more than one
distinct species. In our study, we review the Exostoma species found in Thailand; three species are recognized, of
which two (E. effrenum and E. peregrinator) are described herein as new. Because the third species (E. berdmorei)
is poorly described and diagnosed in existing literature, we also provide a redescription of this species here.
Material and methods
Measurements were made point to point with dial calipers and data recorded to tenths of a millimeter. Counts and
measurements were made on the left side of specimens whenever possible. Subunits of the head are presented as
percentage proportions of head length (% HL). Head length and measurements of body parts are given as
percentage proportions of standard length (% SL). Measurements follow Ng & Rainboth (2001), with the following
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addition: pectoral-pelvic distance is measured from the base of the first pectoral-fin ray to the base of the first
pelvic-fin ray; institutional abbreviations follow Ferraris (2007). The numbers in parentheses following a particular
meristic count refer to the numbers of specimens examined with that count, with an asterisk indicating the
condition for the holotype.
Exostoma berdmorei Blyth, 1860
(Figs. 1, 2)
Exostoma berdmorei Blyth, 1860: 155 (type locality: Tenasserim, Myanmar); Hora & Silas, 1952: 27; Vidthayanon et al., 2005:
106 (text only).
Exostoma labiatum (non M’Clelland)
—
Day, 1870: 525.
Glyptosternum sp.—Hora, 1923: 43
FIGURE 1. Exostoma berdmorei, NIFI 1669, 66.4 mm SL; Thailand: Mae Jawang.
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FIGURE 2. Exostoma berdmorei, live individual approx. 100 mm TL from Salween River drainage, Mae Hong Son Province,
Thailand (specimen not preserved). Photograph by Nonn Panitvong.
Material examined. NIFI 0894 (2), 34.3–54.0 mm SL; Thailand: Mae Hong Son Province, Mae Sariang District,
Huay Po. NIFI 1669 (1), 66.4 mm SL; Tak Province, Tha Song Yang District, Mae Jawang. ZRC 54293 (1), 53.4
mm SL; Thailand: Mae Hong Son Province, left side tributary of Mae Nam Pai, about 14 km N of Mae Sariang at
bridge with road 108.
Diagnosis. Exostoma berdmorei is distinguished from congeners in having a combination of the following
characters: eye diameter 10.1–11.9% HL; head width 18.3–21.1% SL; pectoral-pelvic distance 32.8–36.0% SL;
dorsal-to-adipose distance 9.2–11.7% SL; body depth at anus 11.0–12.7% SL; length of adipose-fin base
32.8–35.8% SL; adipose fin adnate to upper procurrent caudal-fin rays; caudal peduncle length 16.4–19.6% SL;
caudal peduncle depth 9.2–9.7% SL; weakly forked caudal fin; 22–23 preanal vertebrae.
Description. Morphometric data as in Table 1. Head and body broad, very strongly depressed, with paired fins
greatly enlarged to form elongate ovoid adhesive disc with body. Rostral margin rounded in dorsal view,
moderately curved in lateral view. Dorsal profile rising gently and evenly from anterior orbital margin to origin of
dorsal fin, then sloping gently ventrally to end of caudal peduncle. Ventral profile flat to anal-fin base, then sloping
gently dorsally to end of caudal peduncle. Anus and urogenital openings located at vertical through posterior
margin of adpressed pelvic fin. Mouth ventrally directed with broad, thin and papillate lips. Most of premaxillary
tooth patches exposed when mouth is closed. Lower lip with prominent labial fold bearing entire posterior margin,
notched at insertions of inner mandibular barbels. Postlabial groove on lower jaw present, uninterrupted.
Jaw teeth distally flattened, oar-shaped, in two rounded triangular patches narrowly separated at midline on
upper jaw. Teeth on lower jaw situated in two well-separated, roughly triangular patches. Palate edentulous.
Eyes small, dorsolaterally situated, subcutaneous. Gill openings narrow, extending from base of first pectoral-
fin ray to level immediately dorsal to base of posteriormost pectoral-fin ray.
Barbels in four pairs. Nasal barbel moderately long, reaching to middle of orbit. Maxillary barbel flattened,
with flap of skin fringing posterior margin; its tip pointed; ventral surface with numerous striae; extending beyond
base of pectoral fin. Inner mandibular barbel slightly flattened, very short; originating from notch on posterior
margin of lower lip. Outer mandibular barbel situated lateral to inner mandibular barbel; slightly flattened,
reaching to two-thirds of distance between its base and base of first pectoral-fin ray.
Dorsal fin without spine, with i,6 (4) rays. Adipose fin with long base, posterior end adnate to upper procurrent
caudal-fin rays. Anal fin with ii,4,i (4) rays. Caudal fin weakly forked, with i,7,7,i (4) rays; lower lobe slightly
longer than upper. Pelvic fin greatly enlarged, with convex distal margin and i,5 (4) rays; first ray greatly flattened
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and with numerous striae on ventral surface. Pectoral fin greatly enlarged, without spine and with i,8,i (1), i,9 (2) or
i,l0 (1) rays; first ray greatly flattened and with numerous striae on ventral surface. Vertebrae 22+14=36 (2) or
23+14=37 (1).
Coloration. In 70% ethanol: brown on dorsal and lateral surfaces of the head and body, dark yellow on ventral
region. Dorsal and caudal fins brown; dorsal surfaces of pectoral and pelvic fins brown, with light yellow ventral
surfaces. Anal fin dark yellow. Dorsal surface of barbels brown, ventral surface dark yellow. Caudal fin with pale
chevron-shaped band at base and broad, dark W-shaped band on most of middle.
In life (Fig. 2): Olive brown on dorsal and lateral surfaces of head and body, fading to tan on ventral surfaces.
Numerous pale spots densely distributed over dorsal surfaces of head and predorsal region. Dorsolateral surface of
body with three indistinct tan-colored blotches: one below region between dorsal and adipose fins, second below
adipose-fin origin, third below middle of adipose-fin base. Dorsal, pectoral and pelvic fins with dusky fin rays and
hyaline fin membranes. Base of caudal fin with gently crescentic dark-brown bar; middle third of caudal fin with
irregular, dark-brown w-shaped band. Dorsal surface of nasal and maxillary barbels olive brown, ventral surfaces
tan. Mandibular barbels tan.
Distribution. This species is known from the Salween River drainage in Myanmar and western Thailand (Fig.
3). It has been reported from the Sittang River drainage (Thomson & Page, 2006), but this awaits confirmation.
TABLE 1. Morphometric data for Exostoma berdmorei (NIFI 0894, NIFI 1669, ZRC 54293; n=4).
Range Mean±SD
Standard length (mm) 34.3–66.4
%SL
Predorsal length 42.6–44.4 43.5±0.90
Preanal length 73.5–74.2 73.9±0.35
Prepelvic length 47.8–50.9 49.2±1.57
Prepectoral length 15.0–16.6 15.8±0.80
Length of dorsal-fin base 13.1–13.3 13.2±0.12
Length of anal-fin base 6.5–8.2 7.4±0.85
Pelvic-fin length 18.9–19.1 19.0±0.12
Pectoral-fin length 22.4–24.0 23.2±0.80
Caudal-fin length 23.2–23.8 23.6±0.32
Length of adipose-fin base 32.8–35.8 34.7±1.68
Dorsal-to-adipose distance 9.2–11.7 10.4±1.26
Length of caudal peduncle 16.4–19.6 18.4±1.77
Depth of caudal peduncle 9.2–9.7 9.4±0.25
Body depth at anus 11.0–12.7 11.7±0.91
Pectoral–pelvic distance 32.8–36.0 34.0±1.72
Head length 23.1–23.8 23.5±0.36
Head width 18.3–21.1 19.8±1.41
Head depth 10.4–11.8 10.9±0.81
%HL
Snout length 57.0–58.4 57.5±0.78
Interorbital distance 28.0–32.3 29.9±2.19
Eye diameter 10.1–11.9 10.8±0.96
Nasal barbel length 16.8–29.4 24.9±7.03
Maxillary barbel length 67.2–81.6 72.1±8.23
Inner mandibular barbel length 6.3–8.9 7.5±1.32
Outer mandibular barbel length 19.8–25.3 21.7±3.12
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FIGURE 3. Map showing collecting localities of Exostoma species in Thailand examined in this study. The type localities of E.
effrenum and E. peregrinator are shown much further apart than they really are in order to easily distinguish between the two
symbols.
Exostoma effrenum, new species
(Figs. 4, 5)
Type material. Holotype: NIFI 4955, 51.3 mm SL; Thailand: Mae Hong Son Province, Mae La Noi District, Ping
Noi stream close to Doi Om Phai in Chiang Mai Province, 18°23'43"N 98°7'56"E; Mae Hong Son Fisheries Station
staff, December 1998.
Paratypes: NIFI 3765 (2), 51.6–65.0 mm SL; UMMZ 250050 (1), 54.2 mm SL; data as for holotype.
Diagnosis. Exostoma effrenum is distinguished from congeners in having a combination of the following
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characters: eye diameter 11.5–15.0% HL; head width 18.5–19.8% SL; body depth at anus 10.5–12.4% SL; length
of adipose-fin base 25.8–29.0% SL; adipose fin distinctly separate from upper procurrent caudal-fin rays; caudal
peduncle length 20.5–21.3% SL; caudal peduncle depth 5.1–7.0% SL; forked caudal fin; 21–22 preanal vertebrae.
Description. Morphometric data as in Table 2. Head and body broad, very strongly depressed, with paired fins
greatly enlarged to form elongate ovoid adhesive disc with body. Rostral margin rounded in dorsal view,
moderately curved in lateral view. Dorsal profile rising gently and evenly from anterior orbital margin to origin of
dorsal fin, then sloping gently ventrally to end of caudal peduncle. Ventral profile flat to anal-fin base, then sloping
gently dorsally to end of caudal peduncle. Anus and urogenital openings located at vertical through posterior
margin of adpressed pelvic fin. Mouth ventrally directed with broad, thin and papillate lips. Most of premaxillary
tooth patches exposed when mouth is closed. Lower lip with prominent labial fold bearing entire posterior margin,
notched at insertions of inner mandibular barbels. Postlabial groove on lower jaw present, uninterrupted. Dorsal
surface of head covered with conical, moderately dense tubercles.
TABLE 2. Biometric data for Exostoma effrenum (NIFI 4955, NIFI 3765, UMMZ 250050; n=4).
Holotype
NIFI 4955
Range Mean±SD
Standard length (mm) 51.3 51.3–65.0
%SL
Predorsal length 42.1 40.1–42.1 40.9±0.90
Preanal length 70.2 70.2–71.6 70.7±0.66
Prepelvic length 47.2 46.9–51.1 48.4±1.91
Prepectoral length 16.6 15.2–16.6 15.7±0.65
Length of dorsal-fin base 14.8 12.9–15.3 14.1±1.18
Length of anal-fin base 9.7 6.8–9.7 8.2±1.38
Pelvic-fin length 18.1 17.6–20.0 18.5±1.06
Pectoral-fin length 24.2 22.1–24.2 23.4±0.92
Caudal-fin length 25.3 22.5–25.3 23.8±1.22
Length of adipose-fin base 29.0 25.8–29.0 27.4±1.31
Dorsal to adipose distance 11.5 10.3–12.3 11.2±0.93
Length of caudal peduncle 21.2 20.5–21.3 21.0±0.37
Depth of caudal peduncle 7.0 5.1–7.0 6.2±0.83
Body depth at anus 11.7 10.5–12.4 11.8±0.90
Pectoral–pelvic distance 32.9 29.5–32.9 31.7±1.56
Head length 25.3 21.9–25.3 23.4±1.63
Head width 19.7 18.5–19.8 19.4±0.59
Head depth 12.5 10.5–12.5 11.8±0.88
%HL
Snout length 59.7 57.3–64.6 60.9±3.11
Interorbital distance 26.9 26.9–32.7 28.7±2.68
Eye diameter 11.5 11.5–15.0 13.7±1.55
Nasal barbel length 43.1 33.6–43.1 36.8±4.27
Maxillary barbel length 80.0 80.0–88.5 83.4±4.06
Inner mandibular barbel length 9.2 8.0–13.0 10.2±2.14
Outer mandibular barbel length 28.5 22.1–28.5 26.5±2.95
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FIGURE 4. Exostoma effrenum, NIFI 4955, holotype, 51.3 mm SL; Thailand: Ping Noi stream.
Jaw teeth distally flattened, oar-shaped and in two rounded triangular patches narrowly separated at midline on
upper jaw. Teeth on lower jaw situated in two well-separated, roughly triangular patches. Palate edentulous.
Eyes small, dorsolaterally situated, subcutaneous. Gill openings narrow, extending from base of first pectoral-
fin ray to level immediately dorsal to base of posteriormost pectoral-fin ray.
Barbels in four pairs. Nasal barbel moderately long, reaching nearly to posterior orbital margin. Maxillary
barbel flattened, with flap of skin fringing posterior margin; its tip pointed; ventral surface with numerous striae;
extending beyond base of pectoral fin. Inner mandibular barbel slightly flattened, very short; originating from
notch on posterior margin of lower lip. Outer mandibular barbel situated lateral to inner mandibular barbel; slightly
flattened, reaching to two thirds of distance between its base and base of first pectoral-fin ray.
Dorsal fin without spine, with i,6 (4) rays; surfaces of fin rays covered with conical tubercles. Adipose fin with
long base, posterior end separate from upper procurrent caudal-fin rays. Anal fin with ii,4,i (4) rays. Caudal fin
weakly forked, with i,7,7,i (4) rays; lower lobe very slightly longer than upper. Pelvic fin greatly enlarged, with
convex distal margin and i,5 (4) rays; first ray greatly flattened, with numerous striae on ventral surface; dorsal
surfaces of fin rays covered with conical tubercles. Pectoral fin greatly enlarged, without spine and with i,10,i (4)
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rays; first ray greatly flattened, with numerous striae on ventral surface. Dorsal surface of pectoral-fin rays covered
with tubercles. Vertebrae 21+15=36* (2), 22+14=36 (1) or 22+16=38 (1).
Coloration. In 70% ethanol: brown on dorsal and lateral surfaces of head and dorsal surface of body, dark
yellow on ventral region. Dark yellow on lateral surfaces of body immediately dorsal and ventral to lateral
myoseptum, giving impression of two diffuse brown lines on body: one on lateral myoseptum and another along
inter-dorsal region and adipose-fin base. Myotomes along lateral surfaces of body with faint dark outlines. Dorsal
fin brown; dorsal surfaces of pectoral and pelvic fins brown, with ventral surfaces of pectoral and pelvic fins dark
yellow. Anal fin dark yellow. Base of caudal fin with darker, diffuse brown band contiguous with irregular, w-
shaped brown band on most of caudal fin. Dorsal surface of nasal and maxillary barbels brown, ventral surface
dark yellow. Mandibular barbels dark yellow.
In life (Fig. 5): Medium brown on dorsal and lateral surfaces of head and body, fading to tan on ventral
surfaces. Numerous pale spots densely distributed over dorsal surfaces of head and predorsal region. Dorsolateral
surface of body with two indistinct tan blotches: one below adipose-fin origin and another below middle of
adipose-fin base. Dorsal, pectoral and pelvic fins with dusky fin rays and hyaline fin membranes. Base of caudal fin
with gently crescentic dark brown bar; middle third of caudal fin with irregular, dark brown w-shaped band. Dorsal
surface of nasal and maxillary barbels olive brown, ventral surfaces tan. Mandibular barbels tan.
FIGURE 5. Exostoma effrenum, live individual approx. 100 mm SL from Doi Inthanon National Park, Chiang Mai Province,
Thailand (specimen not preserved). Photograph by Nonn Panitvong.
Distribution. This species is known from the upper reaches of the Ping River (one of two main tributaries of
the Chao Phraya River) drainage in northwestern Thailand (Fig. 3). The record from the Doi Inthanon National
Park in Chiang Mai Province, Thailand, is based on photographs of specimens (not preserved; Fig. 5) referable to
this species we have examined.
Etymology. The specific epithet comes from the Latin adjective effrenus, meaning unbridled. This is used in
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allusion to the condition of the adipose fin being distinctly separate from the upper principal caudal-fin rays in this
species.
Exostoma peregrinator, new species
(Figs. 6, 7)
Exostoma berdmorei (non Blyth)—Vidthayanon et al., 2005: 106 (photograph only).
Type material. Holotype: NIFI 3831, 70.2 mm SL; Thailand: Mae Hong Son Province, Mae La Noi District, Ban
Tun, 18°18'31"N 98°8'37"E; C. Vidthayanon, 28 April 1998.
Paratypes: NIFI 3762 (4), 45.6–65.6 mm SL; locality as for holotype; Mae Hong Son Fisheries Station staff,
2005. NIFI 3764 (8), 23.3–67.4 mm SL; UMMZ 250051 (6), 26.2–65.1 mm SL; data as for holotype.
FIGURE 6. Exostoma peregrinator, NIFI 3831, holotype, 70.2 mm SL; Thailand: Ban Tun.
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Diagnosis. Exostoma peregrinator is distinguished from congeners in having a combination of the following
characters: eye diameter 9.3–12.8% HL; dorsal-to-adipose distance 8.2–13.1% SL; length of adipose-fin base
31.7–34.6% SL; adipose fin adnate to upper procurrent caudal-fin rays; body depth at anus 9.9–13.1% SL; caudal
peduncle depth 6.2–8.5% SL; lunate caudal fin; 22–24 preanal vertebrae.
Description. Morphometric data as in Table 3. Head and body broad, very strongly depressed, with paired fins
greatly enlarged to form elongate ovoid adhesive disc with body. Rostral margin rounded in dorsal view,
moderately curved in lateral view. Dorsal profile rising gently and evenly from anterior orbital margin to origin of
dorsal fin, then sloping gently ventrally to end of caudal peduncle. Ventral profile flat to anal-fin base, then sloping
gently dorsally to end of caudal peduncle. Anus and urogenital openings located at vertical through posterior
margin of adpressed pelvic fin. Mouth ventrally directed with broad, thin, papillate lips. Most of premaxillary tooth
patches exposed when mouth is closed. Lower lip with prominent labial fold bearing entire posterior margin,
notched at insertions of inner mandibular barbels. Postlabial groove on lower jaw present and uninterrupted. Dorsal
surface of head covered with conical tubercles.
TABLE 3. Morphometric data for Exostoma peregrinator (NIFI 3831, NIFI 3762, NIFI 3764, UMMZ 250051; n=19)
Holotype
NIFI 3831
Range Mean±SD
Standard length (mm) 70.2 23.3–70.2
%SL
Predorsal length 39.5 38.9–43.4 40.5±1.47
Preanal length 71.4 68.6–74.2 71.8±1.90
Prepelvic length 49.7 45.1–50.9 47.8±2.05
Prepectoral length 15.2 14.3–17.5 15.9±1.22
Length of dorsal-fin base 12.5 12.3–13.8 12.9±0.51
Length of anal-fin base 7.8 6.9–8.3 7.6±0.49
Pelvic-fin length 19.4 16.5–20.7 18.2±1.35
Pectoral-fin length 22.1 19.9–23.8 22.2±1.18
Caudal-fin length 26.4 19.8–26.4 24.8±2.11
Length of adipose-fin base 31.8 31.7–34.6 32.7±1.02
Dorsal to adipose distance 11.3 8.2–13.1 11.4±1.46
Length of caudal peduncle 17.9 17.7–20.9 18.8±1.08
Depth of caudal peduncle 8.0 6.2–8.5 7.9±0.71
Body depth at anus 12.3 9.9–13.1 11.8±1.06
Pectoral–pelvic distance 34.5 29.9–35.3 33.2±1.94
Head length 21.5 21.5–23.9 22.5±0.86
Head width 18.7 18.0–20.0 19.1±0.68
Head depth 9.5 9.1–10.9 10.3±0.68
%HL
Snout length 58.9 56.1–61.2 58.8±1.85
Interorbital distance 33.1 22.2–33.1 29.4±3.38
Eye diameter 12.6 9.3–12.8 11.5±1.08
Nasal barbel length 39.7 30.2–39.7 34.9±3.02
Maxillary barbel length 94.0 69.1–94.0 82.9±8.23
Inner mandibular barbel length 10.6 7.7–12.6 9.8±1.86
Outer mandibular barbel length 25.8 21.4–29.3 25.0±2.86
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FIGURE 7. Exostoma peregrinator, NIFI 3831, holotype, 70.2 mm SL; photograph taken immediately after preservation,
showing color in life.
Jaw teeth distally flattened, oar-shaped, in two rounded triangular patches narrowly separated at midline on
upper jaw. Teeth on lower jaw situated in two well-separated, roughly triangular patches. Palate edentulous.
Eyes small, dorsolaterally situated and subcutaneous. Gill openings narrow, extending from base of first
pectoral-fin ray to level immediately dorsal to base of posteriormost pectoral-fin ray.
Barbels in four pairs. Nasal barbel moderately long, reaching to middle of orbit. Maxillary barbel flattened,
with flap of skin fringing posterior margin; its tip pointed; ventral surface with numerous striae; extending beyond
base of pectoral fin. Inner mandibular barbel slightly flattened, very short; originating from notch on posterior
margin of lower lip. Outer mandibular barbel situated lateral to inner mandibular barbel; slightly flattened,
reaching to two-thirds of distance between its base and base of first pectoral-fin ray.
Dorsal fin without spine, with i,6 (19) rays. Adipose fin with long base, posterior end separate from upper
procurrent caudal-fin rays. Anal fin with ii,4,i (14) or ii,5*(5) rays. Caudal fin lunate, with i,6,7,i* (1) or i,7,7,i (18)
rays; upper and lower first principal rays of approximately same length. Pelvic fin greatly enlarged, with convex
distal margin and i,5 (19) rays; first ray greatly flattened, with numerous striae on ventral surface. Pectoral fin
greatly enlarged, without spine and with i,8,i (2), i,9 (3), i,9,i (7) or i,l0* (7) rays; first ray greatly flattened, with
numerous striae on ventral surface. Dorsal surface of pectoral-fin rays covered with sparse tubercles. Vertebrae
22+14=36 (2), 23+13=36 (2), 22+15=37* (4), 23+14=37 (4), 23+15=38 (1) or 24+14=38 (4).
Coloration. In 70% ethanol: brown on dorsal and lateral surfaces of the head and body, dark yellow on ventral
region. Dorsal and caudal fins brown; dorsal surfaces of pectoral and pelvic fins brown, with light yellow ventral
surfaces. Anal fin dark yellow. Dorsal surface of barbels brown, ventral surface dark yellow. Dorsal half of adipose
fin hyaline; ventral half brown. Caudal fin with brown fin rays and hyaline interradial membranes; dark elongated
elliptical spot on first to third upper and lower principal caudal rays about middle third of fin ray.
In life (Fig. 7): Olive brown on dorsal and lateral surfaces of head and body, fading to dark yellow on ventral
half of flanks and to tan on ventral surfaces. Numerous pale spots densely distributed over dorsal surfaces of head
and predorsal region. Dorsolateral surface of body with two indistinct tan-colored blotches: one below adipose-fin
origin and second below middle of adipose-fin base. Base of adipose fin with melanophores concentrated in a dark
brown, longitudinal band. Dorsal, pectoral and pelvic fins with dusky fin rays and hyaline fin membranes. Base of
caudal fin with gently crescentic dark-brown bar; middle third of caudal fin with irregular, dark brown w-shaped
band; whitish spots on dorsal- and ventralmost tips of caudal fin. Dorsal surface of nasal and maxillary barbels
olive brown, ventral surfaces tan. Mandibular barbels tan.
Distribution. This species is only known from the type locality in the upper reaches of the Ping River (one of
two main tributaries of the Chao Phraya River) drainage in northwestern Thailand (Fig. 3). This is also the type
locality of Oreoglanis sudarai, where the coordinates were erroneously given as 18°35'N 98°10'E (Vidthayanon et
el., 2009), which lies in the Salween River drainage.
Etymology. The specific epithet is the Latin noun meaning “one who travels about”, in reference to the
distribution of this species, which represents the first record of the genus east of the Salween River drainage.
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Discussion
Blyth (1860) described Exostoma berdmorei from an unspecified number of specimen(s) from the “Tenasserim”
[=Tenasserim Provinces] in Myanmar; this encompassed the areas south and east of the Irrawaddy delta and
include the present-day Regions (states) of Kayah, Kayin, Mon, Bago (partially) and possibly Tanintharyi (Fang &
Kottelat, 1999). The type material was initially deposited in the Asiatic Society of Bengal's museum, but later
transferred to the Indian Museum (presently the Zoological Survey of India; Whitehead & Talwar, 1976). It is
generally acknowledged that there are two syntypes (ZSI 597) of E. berdmorei in the ZSI collection; most
references (Thomson & Page, 2006; Ferraris, 2007) mention a third possible syntype (ZSI 600) also deposited
there. However, Hora & Silas (1952) provide reasonable evidence to suggest that ZSI 600 is not a species of
Exostoma. One of us (HHN) has examined one of the two syntypes in ZSI 597, and found the specimen to be in
extremely poor condition, with the entire head and almost all of the fins missing (Fig. 8); the other syntype could
not be located for examination at the time of HHN's visit.
FIGURE 8. Exostoma berdmorei, syntype, ZSI 597, approx. 80 mm SL. Pale bands are artifacts caused by partial drying out of
specimen.
Given the condition of the syntype examined, we can only use information in the original description to verify
our identification of E. berdmorei. The original description describes the adipose fin of E. berdmorei as
"…lengthened but very slight and low, extending nearly to the caudal”, and the caudal fin as having the
“lower...lobe much broader and longer than the upper”. We interpret the former as reference to an adipose fin that is
adnate to the upper procurrent caudal-fin rays (=“extending nearly to the caudal”) and the latter as referring to a
caudal fin that is weakly forked (because a forked caudal fin has distinct lobes while a lunate one does not). The
weakly-forked caudal fin in E. berdmorei is corroborated by data on the syntypes by Day (1870) and Hora & Silas
(1952). Based on this reasoning, we confirm the identity of the Exostoma species from the Salween River drainage
with an adipose fin adnate to the upper procurrent caudal-fin rays and a weakly-forked caudal fin as E. berdmorei.
Exostoma berdmorei is distinguished from E. barakensis in having a more slender body (depth at anus
11.0–12.7% SL vs. 14.0–16.5), a shorter dorsal-to-adipose distance (9.2–11.7% SL vs. 12.6–19.2), the adipose fin
adnate to (vs. separate from) the upper procurrent caudal-fin rays and a weakly forked (vs. emarginate) caudal fin,
from E. effrenum in having a longer adipose fin (length of base 32.8–35.8% SL vs. 25.8–29.0) that is adnate to (vs.
separate from) the upper procurrent caudal-fin rays (compare Figs. 1 and 3), and a shorter, deeper caudal peduncle
(length 16.4–19.6% SL vs. 20.5–21.3; depth 9.2–9.7% SL vs. 5.1–7.0). It differs from E. labiatum in having a
longer adipose fin (length of base 32.8–35.8% SL vs. 26.2) that is adnate to (vs. separate from) the upper
procurrent caudal-fin rays, and from E. peregrinator in having a deeper caudal peduncle (9.2–9.7% SL vs. 6.2–8.5)
and a weakly forked (vs. lunate) caudal fin.
Exostoma stuarti (Hora, 1923) [type locality: Nam-Yak River at Tanja, northern frontier, Myanmar] has been
variously considered a junior synonym of E. labiatum (e.g. Kottelat, 2013), a valid species (Thomson & Page,
2006; Vishwanath & Joyshree, 2007), or species inquirenda (Ferraris, 2007). The problem of the identity of E.
stuarti is compounded by the paucity of recent material from the upper Irrawaddy River drainage in Myanmar.
After examining the holotype of E. stuarti and comparing it to material from the upper Irrawaddy in Myanmar and
China, we follow Hora & Silas (1952) in concluding that E. stuarti is a valid, distinct species diagnosed from E.
vinciguerrae (the only other congener known from the upper Irrawaddy River drainage; see next paragraph) by its
wider head (23.3% SL vs. 18.1–19.6), deeper body (16.3% SL vs. 10.7–11.3) and adipose fin with a shorter base
(30.7% SL vs. 38.0–39.0) that is separate from (vs. adnate to) the upper procurrent caudal-fin rays. Exostoma
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berdmorei differs from E. stuarti in having a larger eye (10.1–11.9% HL vs. 6.5), narrower head (18.3–21.1% SL
vs. 23.3), a more slender body (depth at anus 11.0–12.7% SL vs. 16.3), the adipose fin adnate to (vs. separate from)
the upper procurrent caudal-fin rays, and a deeper caudal peduncle (9.2–9.7% SL vs. 7.7).
The identity of E. chaudhurii (Hora 1923) [type locality: Putao plains, Myanmar] has also not been completely
resolved in recent taxonomic treatments involving Southeast Asian catfishes. Hora & Silas (1952) consider it to be
a synonym of E. vinciguerrae, and Ferraris (2007) considers it to be species inquirenda, while Kottelat (2013)
considers it to be a valid species; no mention of this species is made by Vishwanath & Joyshree (2007). Based on
our comparisons of the holotypes of E. chaudhurii and E. vinciguerrae, we agree with Hora & Silas (1952) that no
significant differences can be found between them and consider the two nominal species conspecific. Exostoma
berdmorei differs from E. vinciguerrae in having a longer pectoral-pelvic distance (32.8–36.0% SL vs. 28.4–31.1)
and fewer preanal vertebrae (22–23 vs. 25–27).
Exostoma effrenum is distinguished from E. barakensis in having a larger eye (11.5–15.0% HL vs. 7.3–11.6), a
shorter dorsal-to-adipose distance (10.3–12.3% SL vs. 12.6–19.2), a more slender body (depth at anus 10.5–12.4%
SL vs. 14.0–16.5) and caudal peduncle (5.1–7.0% SL vs. 9.5–11.1), and from E. labiatum in having fewer preanal
vertebrae (21–22 vs. 25), and from E. peregrinator in having an adipose fin with a smaller base (25.8–29.0% SL vs.
31.7–34.6) and separate from (vs. adnate to) the upper procurrent caudal-fin ray, and a weakly forked (vs. lunate)
caudal fin. It differs from E. stuarti in having a larger eye (11.5–15.0% HL vs. 6.5), narrower head (18.5–19.8% SL
vs. 23.3), more slender body (depth at anus 10.5–12.4% SL vs. 16.3), and longer caudal peduncle (20.5–21.3% SL
vs. 18.1), and from E. vinciguerrae in having a shorter adipose fin (length of base 25.8–29.0% SL vs. 33.8–41.6)
that is separated from (vs. adnate to) the upper procurrent caudal-fin rays, a more slender caudal peduncle
(5.1–7.0% SL vs. 7.6–9.4) and fewer preanal vertebrae (21–22 vs. 25–27).
Exostoma peregrinator is distinguished from E. barakensis in having an adipose fin that is situated nearer the
dorsal fin (dorsal-to-adipose distance 8.2–13.1% SL vs. 12.6–19.2) and adnate to (vs. separate from) the upper
procurrent caudal-fin rays, a more slender body and caudal peduncle (body depth at anus 9.9–13.1% SL vs.
14.0–16.5; caudal peduncle depth 6.2–8.5% SL vs. 9.5–11.1), and from E. labiatum in having an adipose fin with a
longer base (31.7–34.6% SL vs. 26.2) that is adnate to (vs. separate from) the upper procurrent caudal-fin rays. It
differs from E. stuarti in having a larger eye (diameter 9.3–13.1% HL vs. 6.5), the adipose fin adnate to (vs.
separate from) the upper procurrent caudal-fin rays and a more slender body (depth at anus 9.9–13.1% SL vs. 16.3),
and from E. vinciguerrae in having a shorter adipose-fin base (31.7–34.6% SL vs. 38.0–39.0) and fewer preanal
vertebrae (22–24 vs. 25–27).
The two new species (E. effrenum and E. peregrinator) from the Chao Phraya River drainage represents a new
record of the genus east of the Salween River drainage. Their presence here suggests that the Salween and Chao
Phraya river drainages were connected in the geological past (via the Mekong and Red River drainages; Gregory,
1925; Hutchinson, 1989). This hypothesis has also been supported by studies on freshwater reptiles (Claude et al.,
2011; Martin et al., 2012) and molluscs (Attwood & Johnston, 2001). However, as there is no geological evidence
of a large-scale connection between the Chao Phraya and Salween river drainages (Brookfield, 1998; Clark et al.,
2004; Clift et al., 2008), it is likely that the connection may have existed only in the form of localized stream
captures. This hypothesis awaits further corroboration.
Comparative material
Exostoma barakensis: Data from Vishwanath & Joyshree (2007).
E. labiatum: BMNH 1860.3.19.97 (holotype), 73.0 mm SL; India: Arunachal Pradesh, Mishmi Hills.
E. stuarti: ZSI F9742/1 (holotype), 43.0 mm SL; Myanmar: Kachin State, Nam-Yak River at Tanja [=Nam Yak,
approximately 1.5 km S of Langtao, 27°15'N 97°35'E].
E. vinciguerrae: ZSI F9741/1 (holotype of E. chaudhurii), 53.9 mm SL; Myanmar: Kachin State, Putao Plains.
CAS 230826 (31), 22.9–85.4 mm SL; China: Yunnan Province, small tributary to the Dulongjiang near Bapo.
Acknowledgments
We are grateful to James Maclaine (BMNH), David Catania (CAS), Siriwan Suksri (NIFI) and Kelvin Lim (ZRC)
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for permission to examine material under their care, to A. K. Karmakar (ZSI) for facilitating HHN’s visit to the
collection, and to Nonn Panitvong for permission to use his photographs.
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