Paracanthocobitis marmorata, new species

Marmorated Zipper Loach Fig. 11

Holotype. ZMA 119.972, 29.4 mm SL, female, India, Barak drainage, 24.799N, 93.782E, date unknown.

Paratypes. India: Barak drainage, same locality as holotype: ZMA 250.182, 2, 28.2–31.9 mm SL, UF 188251, 1, 33.9 mm SL.

Diagnosis. Paracanthocobitis marmorata is distinguished from all other species of Paracanthocobitis by combination of incomplete lateral line ending just beyond dorsal-fin insertion; 9½–10½ branched dorsal-fin rays; no axillary pelvic lobe; no black stripe along side of body; marmorated pattern of dark lines and blotches between irregularly shaped dorsal saddles dark blotches along side of body; teardrop-shaped black spot on upper margin of caudal-fin base; 8 branched upper caudal-fin rays.

Description. Meristic and morphometric data are in Tables 4 and 5. Body deepest just anterior to dorsal-fin origin; slightly compressed before dorsal fin, strongly compressed postdorsally. Head depressed, snout gently rounded to slightly pointed when viewed dorsally or laterally. Dorsal-fin origin far in front of pelvic-fin origin; distal margin convex. Pectoral fin 0.19–0.22 SL, not reaching pelvic fin; pelvic fin 0.15–0.17 SL, not reaching anal fin; caudal fin emarginate. Lateral line incomplete, reaching at most to just past dorsal-fin insertion with 25–31 pores. No axillary pelvic lobe. Mouth arched with heavily papillated lips; upper lip with 3–5 rows of papillae, continuous with large pads on lower lip. Three pairs of barbels; inner rostral barbel extends to or slightly past base of maxillary barbel, maxillary barbel and outer rostral barbel extend to or slightly past eye. Body covered with scales; 9½ branched dorsal-fin rays; 9–10 pectoral-fin rays; 5–6 pelvic-fin rays; 5½ branched anal-fin rays; 8 branched upper caudal-fin rays; 8 branched lower caudal-fin rays. Suborbital flap in male. Maximum SL 33.9 mm female.

Body yellow-brown with numerous, irregular and poorly defined dark brown dorsal saddles; dark blotches along lateral line extending onto lower side of body; dark brown marmorated pattern between saddles and lateral blotches, usually ending after dorsal-fin insertion. No dark stripe along side. Dark spots and blotches on head; uninterrupted black bar from eye to tip of snout. Ocellus near upper margin of caudal peduncle, small teardropshaped black spot in center; 3–6 concentric rows of dark spots in dorsal fin, 2–3 rows of dark spots in anal fin, 4–6 dark bands on caudal fin.

Comparisons. Paracanthocobitis marmorata differs from all other species of Paracanthocobitis except P. zonalternans, P. phuketensis, P. nigrolineata, and P. triangula, in having an incomplete lateral line ending near the dorsal-fin insertion (vs. lateral line to the end of the caudal peduncle) and 9½–10½ (vs.>10½) branched dorsal-fin rays. Paracanthocobitis marmorata differs from P. zonalternans, P. phuketensis, P. nigrolineata, and P. triangula in having a dark marmorated pattern between the dorsal saddles and lateral blotches and a teardrop-shaped (vs. circular or triangular) black spot on the upper margin of the caudal-fin base, and in not having an axillary pelvic lobe (rarely present in P. phuketensis). Paracanthocobitis marmorata further differs from P. zonalternans and P. nigrolineata in not having black pigment extending onto the pectoral-fin base.

Distribution. Paracanthocobitis marmorata is known from the Barak drainage of Assam, India (Fig. 5).

Etymology. The epithet marmorata refers to the marmorated pattern on the nape and between the dorsal saddles and lateral blotches in lieu of the black stripe along the side of the body typical of other members of the P. zonalternans complex.

Two of the five species in the P. zonalternans complex, P. marmorata and P. triangula, are quite distinctive morphologically. The other three species, P. zonalternans, P. nigrolineata, and P. phuketensis, are similar to one another morphologically and distributed in a narrow geographic area, north to south in the Salween, Mae Khlong, and peninsular drainages (Fig. 5). Despite the high degree of morphological similarities found across these three species, the genetic distances in the mitochondrial marker are moderately large, ranging from 7.6% between P. zonalternans and P. phuketensis to 9.3% between P. nigrolineata and P. phuketensis (Table 3), suggesting that the species are reproductively isolated from each other even though morphological changes are less pronounced. Paracanthocobitis phuketensis, distributed in several rivers draining to the Gulf of Thailand and to the Andaman Sea, shows the greatest intraspecific genetic variation of the group. This variation should be explored in more detail for historical and ecological explanations.

Molecular data agree with the hypothesis proposed by Singer & Page (2015) that the P. zonalternans species complex forms a clade separate from the P. botia clade, represented here (Fig. 1) by P. maekhlongensis, P. pictilis, and P. mandalayensis. In addition, the genetic distances among species of the P. botia clade, which are very distinct morphologically from one another, are less than those found between P. zonalternans and P. nigrolineata and P. phuketensis.

Šlechtová et al. (2007) found Acanthocobitis to be sister to P. zonalternans plus P. botia (identifications of the Paracanthocobitis species are uncertain, but almost certainly represent the P. zonalternans and P. botia clades). However, more specimens and tissues from both major clades within Paracanthocobitis and from the sister genus Acantocobitis are needed to confirm relationships among the species in these genera as well as relationships of these genera to other nemacheilids.

Kottelat (2012) listed Cobitis chlorosoma McClelland, 1839 as a synonym of Acanthocobitis zonalternans. The original description for C. chlorosoma is very short: “Light green, clouded with a darker green, caudal and dorsal marked with spots in transverse rows. D.11: P.12: V.8: A.6: C.18. Hab. Upper Assam.” Text with a drawing (plate 52, fig. 3) of the species accompanying the description states: “Light green, clouded with dark olive green above the lateral line, fins tinged with red, dorsal and anal slightly barred, snout short, six cirri." The only species of Paracanthocobitis known from Assam is P. botia, which has counts that agree with those given by McClelland for C. chlorosoma (Singer & Page 2015), and a pigment pattern very similar to that shown in the drawing of C. chlorosoma (McClelland, 1839: pl. 52). Most species of Paracanthocobitis have a greenish cast and often have fins tinged with red. Paracanthocobitis zonalternans is an exception, being light brown or yellowish with bold black spots or a black stripe along the lateral line. Acanthocobitis pavonacea, also described by McClelland (1839) from Assam and shown on the same plate as C. chlorosoma, has a distinctly pointed caudal fin and 17 or more branched dorsal-fin rays, unlike that shown for C. chlorosoma, which is here considered a synonym of P. botia.