Paracanthocobitis hijumensis, Rime & Tamang & Das, 2022

Rime, Gepi, Tamang, Lakpa & Das, Debangshu Narayan, 2022, Paracanthocobitis hijumensis, a new species of zipper loach from the Arunachal Himalaya, northeastern India (Cypriniformes: Nemacheilidae), Zootaxa 5115 (1), pp. 122-130 : 123-127

Paracanthocobitis hijumensis , new species

( Fig. 1–2 )

Type material. Holotype. RGUMF 0567 , holotype, 63.6 mm SL, female; India: Arunachal Pradesh, West Siang District, Hijum River, an eastward-flowing tributary of the Siang River , at Pidi Rime village , 28°06ʹ11ʺN 94°40ʹ34ʺ E; 441 m asl., coll. Gepi Rime & party, 19 March 2021.

Paratypes. RGUMF 0568 , 9 (5 females and 4 males), 46.5–61.6 mm SL; ZSI / APRC /P-1896, 03 (2 females and 1 male), 50.8–65.6 mm SL; same data as holotype .

Diagnosis. Paracanthocobitis hijumensis is distinguished from members of the P. zonalternans species complex ( P. zonalternans , P. nigrolineata, P. marmorata, P. triangula, and P. phuketensis ) in having a larger body size (46.5–65.6 mm SL vs. <45 mm SL), a complete (vs. an incomplete) lateral line terminating at the end of caudal peduncle (vs. at, or just beyond the dorsal-fin insertion); from members of the P. mandalayensis species complex (P. canicula, P. maekhlongensis, P. mandalayensis and P. pictilis ) by having suborbital flap (vs. suborbital groove) in males and in having fewer dorsal-fin branched rays (9½–10½ vs. 10½–13½), longer head (23.8–26.0% SL vs. 18.0– 20.2); and from members of the P. botia species complex (P. abutwebi, P. aurea, P. botia , P. mooreh , P. urophthalma, P. linypha, P. mackenziei , P. adelaideae, and P. rubidipinnis ) by the following combination of characters: presence of axillary pelvic lobe (vs. lacking); greater predorsal distance (47.9–51.8% SL vs. 40.2–47.4); greater prepelvic distance (52.3–58.8% SL vs. 40.2–50.9); longer head (23.8–26.0% SL vs. 16.4–23.3); deeper body (18.4–23.1% SL vs. 12.5–17.4), smaller eye (14.2–22.5% SL vs. 23.6–40.9) and fewer dorsal-fin branched rays (9½ (12)–10½ (1) vs. 10½–15½). Remaining combinations of characters distinguishing the new species from its congeners are provided in the Discussion.

Description. For general appearance, see Figure 1 . Biometric and meristic data are provided in Tables 1 and 2 respectively. Body moderately elongated, not greater than 65.6 mm SL, anterior body between pectoral-fin and dorsal-fin origin cylindrical, and thereafter greatly compressed to caudal-fin base; body deepest and widest at dorsal-fin origin, or just anterior to it. Predorsal profile abruptly rising from tip of snout to nostril and then evenly rising up to dorsal-fin origin except slight depression on occipital margin, postdorsal body sloping gently ventrally to caudal-fin base. Ventral profile almost flat to anal-fin origin, except slightly bulging abdomen in females, anal-fin base slightly rising, followed by horizontal to caudal-fin base.

Head moderately depressed dorsally and flat ventrally, triangular when viewed dorsally, with obtusely rounded snout, lateral margin of head decreasing from pectoral-fin origin to tip of snout. Mouth inferior, arched, gape about twice as wide as long with well developed papillated lips; upper lip with 3–4 rows of papillae, contiguous with lower lip, lower lip with large pads on either side; pads thick, bulbous and densely papillated, both pads in contact anteriorly with a narrow median interruption in between. A small processus dentiformis on middle of upper jaw, hidden behind lip. Median notch in lower jaw absent. Nostril situated closer to anterior margin of eye than to tip of snout, anterior nostril tubular and erected, pierced at tip; posterior nostril elliptical, without tube. Eye slightly ovoid, dorsolaterally situated at middle of head. Deep suborbital slit in male with free posterior flap, flap postero-ventrally directed, its tip obtusely pointed. Three pairs of barbels (one maxillary and two rostral) slightly dorsoventrally depressed with broad base, tapering to pointed tip. At vertical: Inner rostral barbel extending to anterior margin of nostril, outer rostral barbel extending to anterior orbital margin or slightly past it, maxillary barbel extending to posterior orbital margin or slightly past it.

Body embedded with minute scales, deeply embedded on ventral surface between isthmus and anal-fin origin. Lateral line complete, with 85–105 pores, anterior pores closely set, posterior pores more distantly set.

Dorsal fin origin near middle of body; fin with 4 simple and 9½*(12) or 10½ (1) branched rays, anterior margin slightly arched distally, distal margin straight. Pectoral fin with 1 simple and 11 branched rays, tip of adpressed fin not reaching vertical through dorsal-fin origin. Inter-pectoral-fin distance twice as wide as inter-pelvic distance. Length of pectoral fin equal to distance between pectoral-fin origin and naris. Pelvic fin horizontally flattened with 1 simple and 7 branched rays, origin below the bases of 3 rd –4 th branched dorsal fin rays, adpressed fin extending slightly more than half distance to anal-fin origin. Interpelvic fin distance equal to snout length. Axillary pelvic lobe present, prominent. Anal fin with 3 simple and 5 branched rays, adpressed tip extending close to base of first procurrent ray of caudal fin. Caudal fin slightly emarginate, with 8+8 branched rays. Anus situated closer to analfin origin than to pelvic-fin origin. Cephalic lateral line system with 6 supraorbital, 4 temporal, 12–13 infraorbital, 10–11 preoperculo-mandibular, 3 supratemporal pores, and minute pores in front of nares medially.

Coloration. In preservative, dorsum of head and body background greyish dusky brown, rest of head and body light yellowish cream, except milky white abdomen. All marks on head and body greyish dark brown. All barbels ventrally cream with clusters of minute brown spots dorsally. Dorsal fin hyaline, with 4–5 longitudinal rows of dark brown spots on reticulated rays; caudal fin with 3*(3)– 4(10) complete rows of dark brown spots on reticulated rays, appearing as V-shaped bars, and 1–3 bars incomplete. Caudal fin with 4–6 vertical rows of spots on rays. Other fins hyaline. In life, no gray color background and all marks on body, head and fins dark brown and black ocellus at upper margin of caudal fin. Ocellus fused with light brown marks below.

Head with black ‘V’ to arch-shaped mark in front of nostrils, followed by black spot; 2–3 parallel transverse dark spots or short elongate marks on top of head: 2 spots on internarial, 3 spots on interorbital, and 1 spot in middle between the level of posterior orbital and occipital margins. Narrow dark streak between orbit and base of outer rostral barbel, oblique (postero-ventrally directed) short elongate mark on preopercle just below orbit, and cluster of spots on operculum. Dorsum with 10–13 dark saddles in total: 10 (2), 11*(7), 12 (2) or 13 (2), divided into 4 (4)–5*(9) on the predorsum, 2*(6)–3 (7) subdorsal, and 3 (2), 4*(9), 5(1) or 6(1) postdorsal; 3*–5 short and indistinct saddles present between primary predorsal saddles in 4 adult specimens (55.7–65.6 mm SL). Predorsal saddles narrow, becoming broader at middle, pointed at the end, strongly slanted (posteroventrally), 1–2 saddles sometimes touching lateral line; subdorsal saddles less slanted, post-dorsal saddles almost vertical. Flank with 2–3 (usually 2) rows of ovoid to elliptic blotches—first row with 5–10 small blotches: 5(1), 6(1), 7(2), 8(2), 9(4), 10*(3) running above and sometime in contact with lateral line; second row with 8–11: 8(4), 9*(5), 10(3), 11(1) ovoid to elliptic blotches, running below lateral line, except its upper end touching or crossing lateral line above; and third row with 1–6 small ovoid blotches: 1(5), 2*(3), 3(2), 4(1), 6(1), 0(1), running just below second row, absent in 1 individual.

Sexual dimorphism. Adult males exhibit deep suborbital slit, with free posterior flap on cheek, extending from posterior base of maxillary barbel to past anterior orbital margin, a character absent in females ( Fig. 2A, B ). Of the 13 specimens collected, 4 were males (46.5–55.7 mm SL) and 9 females (53.2–65.6 mm SL).

Distribution and habitat: The new species is so far known only from the Hijum River, which flows through Pidi Rime village in West Siang District, Arunachal Pradesh, northeastern India ( Fig. 4 ). It is a tributary of the Siyom River, which eventually meets with the Siang River to the east and forms the headwaters of the Brahmaputra River in Assam. Habitat at the type locality comprised a clear, moderate to fast-flowing stream dominated by medium- to large-sized boulders, and rarely, sand and small gravel ( Fig. 3 ). Riparian vegetation comprised of shrubs and small trees along the banks, and small to larger trees along the adjacent hills. Co-occurring fishes include members of the genus Schizothorax, Garra, Opsarius, Devario, Danio, Aborichthys, Psilorhynchus, Amblyceps, Pseudecheneis, and Exostoma.

Etymology. The species name is derived from name of the type locality, the ‘Hijum’ River. An adjective.

Figures

FIGURE 1. Paracanthocobitis hijumensis, 63.6 mm SL, RGUMF 0567, holotype, female; (A) dorsal, (B) lateral, and (C) ventral views.

FIGURE 2. Paracanthocobitis hijumensis (A) RGUMF 0568, 53.2 mm SL, paratype, male, showing suborbital slit and postero-ventrally directed free posterior flap. (B) RGUMF 0567, holotype, 63.6 mm SL, female, without suborbital slit or flap. (C) ZSI/APRC/P-1896, 1, paratype, 65.6 mm SL, female (C) showing well developed papillated lips and pads. (D) RGUMF 0567, holotype, 63.6 mm SL, female, showing triangular axillary pelvic lobe.

FIGURE 3. Type locality of Paracanthocobitis hijumensis near Pidi Rime village, Hijum River, West Siang District, Arunachal Pradesh, India.

FIGURE 4. Map of Arunachal Pradesh showing drainage systems and the type locality of Paracanthocobitis hijumensis (indicated by black filled circle).