Glyptothorax igniculus, Ng, Heok Hee & Kullander, Sven O., 2013

Ng, Heok Hee & Kullander, Sven O., 2013, Glyptothorax igniculus, a new species of sisorid catfish (Teleostei: Siluriformes) from Myanmar, Zootaxa 3681 (5), pp. 552-562 : 553-559

Glyptothorax igniculus , new species

( Fig. 1 )

Type material. Holotype: NRM 64520, 65.5 mm SL; Myanmar: Sagaing Region, left bank of Myittha River approximately 8 km NE by E of Kalaymyo, 23°13'41"N 94°7'59"E; S. O. Kullander & T.- Y. Liao, 30 March 2008. Paratypes: NRM 64521 (1), 67.3 mm SL; data as for holotype. NRM 58846 (1), 62.5 mm SL; NRM 58845 (1), 71.3 mm SL; ZRC 54115 (1), 58.5 mm SL; NRM 58928 (1), 54.7 mm SL; Myanmar: Sagaing Region, market in Tamu; S. O. Kullander & T.- Y. Liao, 29 March 2008.

Diagnosis. Glyptothorax igniculus is distinguished from all congeners in the Irrawaddy River drainage by its thoracic adhesive apparatus, in which the central depression is almost completely enclosed posteriorly by the skin ridges that make up the apparatus, instead of open caudally or, in G. burmanicus , completely closed. It further differs from G. burmanicus in having a larger eye (diameter 10.4–12.7% HL vs. 6.3–10.0), a longer dorsal-fin spine (16.9–21.6% SL vs. 11.9–14.7), and shorter prepectoral (17.1–21.7% SL vs. 22.3–25.4) and prepelvic lengths (47.0–51.3% SL vs. 52.8–59.4).

Besides the morphology of the thoracic adhesive apparatus, G. i g n i c u l u s differs from G. longicauda in having a longer dorsal-fin spine (16.9–21.6% SL vs. 11.5–14.4), a shorter dorsal-to-adipose distance (19.8–24.6% SL vs. 25.9–26.9), deeper body (depth at anus 15.2–16.4% SL vs. 11.0–12.5) and caudal peduncle (8.2–9.7% SL vs. 5.4– 6.2) and fewer total vertebrae (35–36 vs. 43–44), and from G. longjiangensis in having a wider head (20.3–21.8% SL vs. 14.5–19.3), rounded tubercles (vs. large anastomosing plaques bearing parallel unculiferous ridges) on the dorsal surface of the head, deeper body (depth at anus 15.2–16.4% SL vs. 11.7–14.4) and caudal peduncle (8.2– 9.7% SL vs. 4.6–7.6) and fewer total vertebrae (35–36 vs. 38–39). Glyptothorax igniculus is further distinguished from G. m i n i m a c u l a t u s in having fewer total vertebrae (35–36 vs. 40–43), from G. m i n u t u s in reaching to a much larger size (to at least ca. 70 mm SL vs. ca. 27 mm SL) and an almost uniform body (vs. with dark saddles overlying a pale body), and from G. ngapang in having a longer nasal barbel (30.1–35.5% HL vs. 15.0–28.7), a wider head (20.3–21.8% SL vs. 13.2–19.7) and a deeper caudal peduncle (8.2–9.7% SL vs. 5.3–6.9). Glyptothorax igniculus further differs from G. panda in having a larger eye (diameter 10.4–12.7% HL vs. 15.7–18.4), longer dorsal-fin spine (16.9–21.6% SL vs. 10.3–15.3), a deeper body (depth at anus 15.2–16.4% SL vs. 10.4–11.8) and a deeper caudal peduncle (8.2–9.7% SL vs. 5.3–6.2), from G. rugimentum in lacking (vs. with) the ridges of the thoracic adhesive apparatus extending onto the gular region, having a shorter head (25.3–28.2% SL vs. 28.4–31.2) and predorsal distance (35.6–37.4% SL vs. 39.9–42.8), a longer postadipose distance (18.8–20.8% SL vs. 14.4– 17.6) and a deeper caudal peduncle (8.2–9.7% SL vs. 6.1–7.6), and from G. ventrolineatus in having a longer adipose-fin base (13.9–15.8% SL vs. 9.3–11.1).

Seven other species of Glyptothorax from the Indian subcontinent are known to have the skin ridges of the thoracic adhesive apparatus almost or wholly enclosing the central depression posteriorly, viz., G. cavia (Ganges- Brahmaputra river system), G. g a rh w a l i (Ganges River drainage), G. jalalensis (Indus River drainage), G. j a y a r a m i (Kolodyne River drainage), G. k a s h m i re n s i s (Indus River drainage), G. maceriatus (Surma-Meghna river system), and G. stocki (Indus River drainage). Glyptothorax igniculus differs from G. cavia in having the depressed central in the thoracic adhesive apparatus lanceolate (vs. ovoid) and with a single, non-diverging series (vs. double, diverging series) of striae running along its edges, a deeper caudal peduncle (8.2–9.7% SL vs. 4.8–6.4), from G. garhwali in having a longer anal-fin base (14.1–17.8% SL vs. 12.7–12.8), and postadipose length (18.8–20.8% SL vs. 16.4–18.0), and from G. jalalensis in having a shorter adipose-fin base (13.9–15.8% SL vs. 19.1) and a more slender caudal peduncle (8.2–9.7% SL vs. 10.9). It is further distinguished from G. j a y a r a m i in having a shorter pectoral fin (21.2–26.1% SL vs. 26.3–27.8), lacking (vs. with) plicae on the ventral surfaces of the first pectoral- and pelvic-fin elements, having a deeper body (depth at anus 15.2–16.4% SL vs 13.1–15.0) and caudal peduncle (8.2–9.7% SL vs. 5.5–7.9), from G. k a s h m i re n s i s in having a single, non-diverging series (vs. double, diverging series) of striae running along the edges of the central depression in the thoracic adhesive apparatus, a more slender body (depth at anus 15.2–16.4% SL vs. 17.1–17.7), from G. maceriatus in having a deeper body (depth at anus 15.2–16.4% SL vs. 11.3–13.8) and caudal peduncle (8.2–9.7% SL vs. 6.4–7.6), and from G. s t o c k i in lacking (vs. having) both a distinct pale midlateral stripe on the body and distinct dark submarginal stripe along each lobe of the caudal fin.

Description. Morphometric data as in Table 1. Head depressed, body subcylindrical. Dorsal profile rising evenly from tip of snout to origin of dorsal fin, sloping gently ventrally from origin of dorsal fin to end of caudal peduncle. Ventral profile flat to anal-fin base, 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. Caudal peduncle depth 2.2–2.8 times in its length. Skin almost smooth, with minute, rounded tubercles on sides of body. Lateral line complete, mid-lateral. Vertebrae 18+17=35 (1), 17+19=36 (1) or 18+18=36* (3).

Head depressed, broad; triangular in lateral view. Snout prominent. Anterior and posterior nares large, separated only by base of nasal barbel. Gill openings broad, extending from immediately ventral to post-temporal to isthmus. Bony elements of dorsal surface of head covered with thick, tuberculate skin. Eye ovoid, its horizontal axis longest; located entirely in dorsal half of head.

Barbels in four pairs. Maxillary barbel long slender; extending just beyond base of last pectoral-fin ray. Nasal barbel slender, extending to just beyond anterior orbital margin. Inner mandibular-barbel origin close to midline, extending to two-thirds distance between its base and that of pectoral spine. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending just beyond base of pectoral spine.

Mouth inferior, premaxillary tooth band not exposed with mouth closed. Oral teeth small, villiform; in irregular rows on all tooth-bearing surfaces. Premaxillary teeth in a single broad semilunate band. Dentary teeth in narrow crescentic band that does not reach midline.

Thoracic adhesive apparatus present, consisting of ridges of skin (striae) in elliptical field extending from isthmus to level of last pectoral-fin ray base, with lanceolate median depression on posterior half almost enclosed posteriorly by skin ridges ( Fig. 2 ). Striae uninterrupted; medial striae orientated anteriorly, lateral ones anterolaterally.

Pectoral fin with i,8,i (1), i,9* (4) or i,9,i (1) rays; posterior fin margin slightly concave. Pectoral spine very broad and covered with thick skin. Anterior spine margin smooth, its posterior margin with 9–12 serrae. Ventral surface of spine smooth and without plicae. Dorsal fin above anterior third of body, with i,6 (6) rays; fin margin convex; spine broad, straight; with 0–8 serrae on posterior margin. Adipose fin with anterior margin straight or very slightly concave, posterior margin angular. Procurrent rays symmetrical, extending only slightly anterior to fin base. Vertical through anal-fin origin posterior to that through adipose-fin origin. Pelvic fin with slightly convex margin and i,5 (6) rays; tip of adpressed fin not reaching anal-fin origin. Ventral surface of first pelvic-fin ray smooth and without plicae. Vertical through pelvic-fin origin posterior to that through posterior end of dorsal-fin base. Anal fin with straight anterior margin, straight or slightly concave posterior margin; with iii,8,i (2), iv,8 (1), iv,8,i (2) or iv,9* (1) rays. Caudal fin strongly forked, with lower lobe very slightly longer than upper lobe and i,7,8,i (6) principal rays.

Coloration. In 70% alcohol: dorsal and lateral surfaces of head and body brown fading to cream on ventral surfaces. Faint pale mid-dorsal spot at base of doorsal-fin spine. Dorsal, pectoral, pelvic, anal and caudal fins also brown, particularly on bases and rays. Adipose fin dark brown basally, fading to lighter brown along distal margin. Nasal and maxillary barbels brown dorsally, cream ventrally; all mandibular barbels cream.

Habitat. The type locality of G. i g n i c u l u s is a wide (ca. 200 m), turbid river with moderate current and a substrate comprised of clay. Associated fishes include Crossocheilus burmanicus (Cyprinidae) , Danio albolineatus (Cyprinidae) , ‘ Pethia’ meingangbii ( Cyprinidae ), Puntius chola (Cyprinidae) , Raiamas guttatus (Cyprinidae) , Mystus falcarius (Bagridae) , Heteropneustes fossilis (Clariidae) , Glyptothorax rugimentum (Sisoridae) , Xenentodon cancila (Belonidae) , Badis ferrarisi (Badidae) , Channa gachua (Channidae) , C. panaw (Channidae) , Trichogaster labiosa (Osphronemidae) and Tetraodon cutcutia (Tetraodontidae) .

Etymology. The specific name comes from the Latin noun igniculus , meaning a little flame, in allusion to the lanceolate, flame-shaped central depression in the thoracic adhesive apparatus that is nearly completely enclosed by skin ridges caudally.

Distribution. Known from the Myittha River, a tributary of the Chindwin River in western Myanmar ( Fig. 3 ).

Comparative morphometry. We carried out a morphometric analysis of the four species of Glyptothorax found sympatrically in the Chindwin ( G. burmanicus , G. i g n i c u l u s, G. ngapang and G. rugimentum ). In proportional measurements (Table 1), Glyptothorax igniculus differs from G. burmanicus in shorter prepelvic and prepectoral lengths; longer dorsal spine and larger eye; from G. ngapang in narrower head and longer nasal barbel; from G. rugimentum in shorter predorsal and head lengths, and longer postadipose length; and from G. burmanicus , G. ngapang , and G. rugimentum in deeper caudal peduncle. The SL distribution of the G. igniculus is too restricted to obtain a strong linear correlation for the caudal peduncle depth, but it is clearly the most important measurement separating from all three species compared with (Table 1, Fig. 4A).

FIGURE 4. Morphometric analysis of Glyptothorax igniculus and sympatric taxa. A Biplot of caudal peduncle depth ( Y) against Standard length (X) with linear regressions ( G. igniculus , 1.14+0.07*SL, R2 = 0.434; G. burmanicus , 1.09+0.09*SL, R2= 0.980; G. ngapang , 0.3+0.07*SL, R2 = 0-985; G. rugimentum , 0.41+0.07*SL, R2=0.816); two largest G. burmanicus not included to improve visual clarity in overlapping size range. B–D Plots of scores of principal components.

In the PCA (Fig. 4B–D, Table 2 ), loadings on component I are of roughly the same magnitude, and the variance only 88%, reflecting the similar size of specimens except two large G. b u r m a n i c u s. Also other components seem to reflect lack of variation, as seen in the only slight accumulation of variance and low eigenvalues. Component II separates G. ngapang from the rest (Fig. 4B–C), and is dominated by the nasal and outer mandibular barbels. The third component is dominated by the dorsal spine length, with the nasal barbel and orbital diameter also contributing to the variance. The fourth component is dominated by caudal peduncle depth and orbital diameter. The most distinct clustering is obtained in contrasting Components II and III (Fig. 4C), and the most distinct cluster of G. i g n i c u l u s from the rest is obtained by contrasting Components III and IV (Fig. 5), reflecting the orbital diameter and caudal peduncle depth.

Figures

FIGURE 1. Glyptothorax igniculus, NRM 64520, holotype, 65.5 mm SL; dorsal, lateral and ventral views.

FIGURE 2. Thoracic adhesive apparatus of Glyptothorax igniculus, NRM 64520, holotype, 65.5 mm SL.

FIGURE 3. Map showing collecting localities of Glyptothorax igniculus. Open symbol indicates type locality.