Exostoma peregrinator, Ng, Heok Hee & Vidthayanon, Chavalit, 2014

Ng, Heok Hee & Vidthayanon, Chavalit, 2014, A review of the glyptosternine catfish genus Exostoma Blyth 1860 from Thailand, with descriptions of two new species (Teleostei: Siluriformes), Zootaxa 3869 (4), pp. 420-434 : 428-430

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.

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.

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.

Figures

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.

FIGURE 6. Exostoma peregrinator, NIFI 3831, holotype, 70.2 mm SL; Thailand: Ban Tun.

FIGURE 7. Exostoma peregrinator, NIFI 3831, holotype, 70.2 mm SL; photograph taken immediately after preservation, showing color in life.

Tables

TABLE 3. Morphometric data for Exostoma peregrinator (NIFI 3831, NIFI 3762, NIFI 3764, UMMZ 250051; n = 19)

Standard length (mm)	Holotype NIFI 3831 70.2	Range 23.3–70.2	Mean±SD
%SL Predorsal length Preanal length	39.5 71.4	38.9–43.4 68.6–74.2	40.5±1.47 71.8±1.90
Prepelvic length Prepectoral length Length of dorsal-fin base	49.7 15.2 12.5	45.1–50.9 14.3–17.5 12.3–13.8	47.8±2.05 15.9±1.22 12.9±0.51
Length of anal-fin base Pelvic-fin length Pectoral-fin length	7.8 19.4 22.1	6.9–8.3 16.5–20.7 19.9–23.8	7.6±0.49 18.2±1.35 22.2±1.18
Caudal-fin length Length of adipose-fin base Dorsal to adipose distance	26.4 31.8 11.3	19.8–26.4 31.7–34.6 8.2–13.1	24.8±2.11 32.7±1.02 11.4±1.46
Length of caudal peduncle Depth of caudal peduncle Body depth at anus	17.9 8.0 12.3	17.7–20.9 6.2–8.5 9.9–13.1	18.8±1.08 7.9±0.71 11.8±1.06
Pectoral–pelvic distance Head length Head width	34.5 21.5 18.7	29.9–35.3 21.5–23.9 18.0–20.0	33.2±1.94 22.5±0.86 19.1±0.68
Head depth %HL Snout length	9.5 58.9	9.1–10.9 56.1–61.2	10.3±0.68 58.8±1.85
Interorbital distance Eye diameter Nasal barbel length	33.1 12.6 39.7	22.2–33.1 9.3–12.8 30.2–39.7	29.4±3.38 11.5±1.08 34.9±3.02
Maxillary barbel length Inner mandibular barbel length Outer mandibular barbel length	94.0 10.6 25.8	69.1–94.0 7.7–12.6 21.4–29.3	82.9±8.23 9.8±1.86 25.0±2.86