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We describe a new species of Stoliczkia from Mizoram, India. Stoliczkia vanhnuailianai sp. nov. is identified as a member of the genus Stoliczkia by distinct scale arrangements on the posterior of the head, and by scales on the body being separated by scaleless skin, and it differs from the two known congeners in body and head scalation. This is only the third specimen of Stoliczkia collected from India, and the sixth reported specimen for the genus. A revised key to the identification of the species of Stoliczkia is provided.

We present a first record for three species of frogs, viz. Amolops indoburmanensis, Euphlictys kalisgraminensis and Polypedates braueri in India based on DNA barcoding data. We also discussed on the records of Amolops spp. in Mizoram and delisted all previous recorded species, viz. A. afghanus, A. kaulbacki and A. marmoratus from the amphibian fauna of Mizoram until further research confirmed their presence, since the data were not sufficient enough for the confirmation of their occurrence and are likely based on misidentification of A. indoburmanensis.

Most studies on the diversity of amphibians in northeast India were based on classical morpho-taxonomy, which have a high probability of errors in species identification. DNA barcoding of amphibians using the mitochondrial 16S rRNA gene has been used successfully for the identification of species and detection of cryptic species. In the present study, we carry out DNA barcoding of two rhacophorid species of the genus Raorchestes and Kurixalus that are not readily identifiable to the species level based on their morphology. Our analysis on the 16S rRNA gene revealed that these species were Raorchestes cangyuanensis and Kurixalus yangi, species which were recorded for the first time and second time from India respectively. We discuss on the records of R. longchuanensis from Bangladesh and India, which were based on the misidentification of R. cangyuanensis. We therefore propose to delist this species from the faunal list of Bangladesh and India. We further raise a question as to why the population of Kurixalus from Motuo, Xizang province of China was assigned as K. naso and not the population described as K. yangi, which is morphologically similar to K. naso and is also recorded from a locality close to the type locality of K. naso.

Stoliczka (1870) described Hylorana nicobariensis from the Nicobar Islands of India. The generic allocation of this enigmatic species is yet to be fully resolved (Chan et al. 2020b) and it has been placed in different genera (Boulenger 1885; Frost et al. 2006; Che et al. 2007; Oliver et al. 2015; Chan et al. 2020a; Chandramouli et al. 2020). As of now, the species is assigned to the genus Indosylvirana (Oliver et al. 2015; Chan et al. 2020b; Frost 2020). Apart from Nicobar archipelago, this species is distributed in the insular regions of southeast Asia (Oliver et al. 2015; Chandramouli et al. 2020; Frost 2020) and the states of Arunachal Pradesh, Assam, Mizoram, Tripura and West Bengal in northeast India (Sarkar et al. 1992, 2002; Sarkar & Ray 2006; Ahmed et al. 2009; Mathew & Sen 2010; Lalremsanga 2011; Lalremsanga et al. 2015, 2016). However, Frost (2020) doubted the records of this species in northeast India. Systematic studies on the herpetofauna of northeast India based on molecular evidence are scanty (Lalronunga et al. 2020a), and species recorded from the area need confirmation (Frost 2020). Recent studies revealed that many species previously recorded from northeast India were based on misidentifications (Das et al. 2019; Giri et al. 2019; Lalronunga et al. 2020b), therefore, a review and revalidation on the herpetofaunal list of the area is warranted. Herein, we examined the identity of the species recorded as I. nicobariensis from northeast India using morphological data and a fragment of 16S rRNA mitochondrial gene.

Xenodermidae is a generally poorly known lineage of caenophidian snakes found in South, East and Southeast Asia. We report molecular phylogenetic analyses for a multilocus data set comprising all five currently recognised genera and including new mitochondrial and nuclear gene sequence data for the recently describedStoliczkia vanhnuailianai. Our phylogenetic results provide very strong support for the non-monophyly ofStoliczkia, as presently constituted, withS. borneensisbeing more closely related toXenodermusthan to the Northeast IndianS. vanhnuailianai. Based on phylogenetic relationships and morphological distinctiveness, we transferStoliczkia borneensisto a new monotypic genus endemic to Borneo,Paraxenodermusgen. nov.We also present new morphological data forP. borneensis.

Badis kaladanensis, a new percoid fish is described from the Kaladan basin of Mizoram, northeast India. It belongs to the Badis badis species group but can be easily distinguished from its congeners, except from B. kanabos and B. tuivaiei, in having a dark blotch on the dorsal fin between the base of 3rd to 5th spines. It is further distinguished from B. kanabos in having more scales in lateral row (27–30 vs. 25–26), more circumpeduncular scale rows (18–20 vs. 16–17) and smaller eye (7.5–8.9% SL vs. 9.5–12.7); and from B. tuivaiei in having fewer vertebrae (28–29 vs. 30–31) and more rakers on the first gill arch (9 vs. 6–8). The analysis of the mitochondrial DNA (coi and cytb) revealed the distinctness of B. kaladanensis from all other Badis species with the interspecific distance ranges from 5.4–20.4%. (coi) and 5.1–26.3% (cytb).

We provide the first molecular phylogenetic data for the following poorly known Northeast Indian snakes: Blythia reticulata and B. hmuifang, Hebius xenura, and Trachischium spp. Based on 1071 bp of cytb, 578 bp of nd4, 509 bp of 16s, 1000 bp of rag1 and 672 bp of cmos, we found support for a monophyletic Blythia being a member of Natricinae, most closely related to Trachischium. Hebius xenura is recovered as nested within species of the recently resurrected genus Herpetoreas, to which we transfer it.

Specimens of a rare rhacophorid frog of the genus Theloderma were collected from Hmuifang, Mizoram, India. Based on their morphology and molecular analysis (16S rRNA), the specimens were identified as Theloderma moloch, a rare species previously recorded only from the Himalayan foothills of India and China. The present record significantly extends the known range of the species and is a first record for the state of Mizoram and Indo-Burma biodiversity hotspot. The uncorrected p-distance between the specimen from Mizoram, NE India and the specimen from Arunachal Pradesh, India (KU169993) and Tibet, China (KU243081) are 0.0% and 1.2% respectively.

Cabdio crassus, a new fish species, is described from the Kaladan River in Mizoram, India. The new species is distinguished from all its congeners by having a ventral keel extending from the middle of the chest, between the posterior base of the pectoral fin and along the abdomen up to the anus (vs. more or less keeled median scales from mid-point of abdomen between posterior base of pelvic fin up to anus in all other Cabdio) and 11½–12½ branched anal-fin rays (vs. 7 in C. jaya and 9 in both C. morar and C. ukhrulensis). It is further distinguished from C. morar and C. ukhrulensis by possessing more lateral-line scales (45–51 vs. 38–42 in C. morar and 35–37 in C. ukhrulensis), more predorsal scales (20–23 vs. 17–18 in C. morar and 14 in C. ukhrulensis) and more lateral transverse scales (½7/1/3½ vs. 5/1/2 in both C. morar and C. ukhrulensis). It also differs from C. jaya in having fewer lateral-line scales (45–51 vs. 52–60), more lateral transverse scales (½7/1/3½ vs. 5/1/3) and more pharyngeal tooth-rows (3 vs. 2). Furthermore, the cytochrome c oxidase sub unit I (coi) gene sequence separates Cabdio crassus from all other Cabdio species (interspecies distance ranges from 7.8–12.3%). The anomalies observed among the GenBank sequences of the genus Cabdio are discussed and resolved.

Based on the first molecular phylogenetic analyses of samples from northeast India, specimens referred to Rhabdops from this region are more closely related to the southeast and east Asian natricine genera Opisthotropis Günther, 1872 and Sinonatrix Rossman & Eberle, 1977 (as well as to New World and western Palearctic natricines) than to peninsular Indian (true) Rhabdops. Morphologically, these northeast Indian populations differ from other natricines by having a single (‘fused’ or unpaired) internasal shield and a single prefrontal shield. Given the morphological and phylogenetic distinctiveness of these northeast Indian populations, we refer them to a new genus, Smithophis gen. nov., and transfer Rhabdops bicolor (Blyth, 1854) to Smithophis bicolor comb. nov. Based on morphological and molecular variation within our northeast Indian sample, we additionally describe Smithophis atemporalis sp. nov. from the state of Mizoram.

Pterocryptis subrisa, a new species of silurid catfish from the Kaladan River drainage in northeastern India, is described in this study. It can be distinguished from congeners by the unique combination of the following characters: supralabial fold extending posteriorly beyond vertical through posterior orbital margin; nearly circular eye; head length 17.6–19.6% SL; head depth 10.6–11.9% SL; dorsal-fin height 2.6–4.7% SL; 2 dorsal-fin rays; pectoral-fin length 11.8–14.0% SL; body depth at anus 14.4–16.7% SL; caudal peduncle depth 6.8–8.5% SL; 66–75 anal-fin rays; confluent anal and caudal fins separated by deep notch; 17 principal caudal-fin rays; and 57 vertebrae. The generic status of Pterocryptis taytayensis is discussed, with this species being reassigned to Ompok.

Neolissochilus kaladanensis sp. nov., a new cyprinid species, is described from the Kaladan River drainage of Mizoram. It differs from all other valid Neolissochilus species in having higher number of gill rakers on the lower arm of the first gill arch (13-14 vs. 12 or below in all the species). The analysis of mitochondrial gene cytochrome c oxidase subunit I (COI) sequences separated N. kaladanensis sp. nov. from all other Neolissochilus and Tor species with an average genetic distance of 6.0%. It is further separated from the morphologically most similar species N. hendersoni and N. soroides by a genetic distance of 6.7% and 6.8%, respectively. Based on the lowest BIC and AICc scores, best fit model for COI dataset was TN93 + G + I, out of 24 different nucleotide substitution models tested. The maximum-likelihood (ML) phylogenetic tree was constructed using the COI sequences of representative Neolissochilus and Tor species. The anomalies observed among the GenBank sequences of the genera Tor and Neolissochilus are also discussed.

We report the clutch size, egg morphometry and timing of oviposition in two snakes, Oligodon albocinctus and Hebius xenura based on specimens from Mizoram, northeast India.

Garra dampaensis, a new cyprinid fish species, is described from the Seling River, a tributary of the Khawthlang Tuipui (Karnaphuli River), in Mizoram, India. The species can be distinguished from all other Garra species, except G. abhoyai, G. lissorhynchus, G. nambulica, G. paralissorhynchus and G. rupecula by the presence of a distinct W-shaped black band on the caudal fin. It can be distinguished from the above mentioned five species in having scales on the breast and belly, shorter vent to anal distance, and by having fewer lateral line scales (27-29 vs. more than 29 in all other species). A key to the species of Garra in the Lissorhynchus complex is provided.

Channa aurantipectoralis , a new species of snakehead of the C. gachua species group, is described from Karnaphuli drainage of Mizoram, India. The species is immediately distinguished from all other snakehead species by its unique coloration in life, specifically its brightly-coloured orange pectoral fins, which lack any spots or stripes; and by the presence of a dark V-shaped blotch on the dorsal surface of the head. It can be further distinguished from all other species of the genus by the combination of the following characters: presence of pelvic fins, a large scale on the ventral surface of the lower jaw, 51–64 lateral-line scales, 34–37 dorsal-fin rays, 23–25 anal-fin rays, 13–14 pectoral-fin rays, 5½–6½ /1/ 7½–8½ transverse scale rows, and the absence of scales on the gular region.

This study describes a new diminutive sisorid catfish from the upper reaches of the Karnaphuli River drainage in northeastern India. The new species can be distinguished from congeners in having a combination of: length of dorsal-fin spine 18.0–21.6% SL; 4–10 serrations on the anterior edge of the dorsal spine; length of pectoral-fin spine 20.7–26.1% SL; length of adipose-fin base 21.5–26.3% SL; body depth at anus 12.3–15.9% SL; caudal peduncle depth 7.5–9.8% SL; caudal peduncle length 17.0–20.5% SL; pale, y-shaped marking on dorsal surface of head; sides of body with pale yellowish patches and irregular bands.

Psilorhynchus kaladanensis , a new psilorhynchid, is described from the Kaladan basin of Mizoram, India. The new species is diagnosed by having the following combination of characters: caudal fin with small but distinct dark brown triangular spot at mid-base, slightly elongated dark mark near base of lower lobe, indistinct V-shaped vertical bar across center, dark brown oblique bar across fin anterior to center; absence of scales on mid-ventral region between pectoral fins; anteriormost branchiostegal ray greatly reduced in length; 32–33 total vertebrae; 30–32 lateral-line scales; caudal fin with 10+9 principal rays.

Psilorhynchus khopai, a new species of Psilorhynchidae, is described from Tuisi River, a tributary of Kaladan River, in Mizoram, India. The species is proposed to be a member of the Psilorhynchus homaloptera species group and can be distinguished from its congeners in having a forked caudal-fin with 9 + 9 principal caudal rays, 14–17 predorsal scale rows, 39–41 lateral-line scale rows, mid-lateral body with 9–12 indistinct small dark brown round markings forming a lateral stripe and, in life, a faint gold stripe along dorsal midline with 4–5 black spots between dorsal fin and caudal fin base.

Schistura maculosa, a new species of loach, is described from Tuingo and Pharsih Rivers, tributaries of Tuivai River (Barak drainage) in Mizoram, northeastern India. It is distinguished from other closely related Schistura species in having an axillary pelvic lobe; an incomplete lateral line; 20-30 narrow black bars on the body; 3-4 rows of black spots horizontally across the dorsal-fin; a slightly emarginate caudal-fin, with 5-7 rows of black spots more or less regularly arranged vertically on rays across the fin, and 8+8 branched caudal-fin rays.

This study describes Pseudolaguvia nubila, a new miniature sisorid catfish from the Kaladan River drainage in northeastern India. Pseudolaguvia nubila can be distinguished from congeners in having a combination of a mottled brown body with yellowish bands, a weakly projecting snout in which the premaxillary teeth are barely exposed when the mouth is closed, head width 19.7-21.7% standard length (SL), eye diameter 10.8-14.0% head length (HL), interorbital distance 25.6-31.8% HL, absence of a pale Y-shaped marking on the dorsal surface of the head and supraoccipital process, a smooth anterior edge of the dorsal spine, dorsal-fin spine length 16.4-19.3% SL, length of dorsal-fin base 15.1-17.3% SL, 7-8 serrations on the anterior edge of the pectoral spine, pectoral-fin spine length 18.1-22.0% SL, dorsal to adipose distance 13.1-16.8% SL, length of adipose-fin base 14.2-15.9% SL, pelvic-fin length 15.8-18.5% SL, body depth at anus 13.9-17.1% SL, caudal-peduncle length 15.7-20.2% SL, caudal-peduncle depth 9.1-11.1% SL, and caudal-fin length 20.3-25.3% SL.