South‐East Asia has an exceptionally high diversity of snakes, with more than 250 snake species currently recorded from Thailand. This diversity likely reflects the diverse range of geographical and climatic conditions under which they live, but the evolutionary history and population genetics of many snake species in South‐East Asia have been little investigated in comparison with morphological studies. Here, we investigated genetic variation in the monocled cobra, Naja kaouthia, Lesson, 1831, across its distribution range in Thailand using mitochondrial DNA (cytochrome b, control region) for ~100 individuals and the nuclear DNA gene (C‐mos) for a small subset. Using population genetic and phylogenetic methods, we show high levels of genetic variation between regional populations of this non‐spitting cobra, including the north‐eastern, north‐central and southern regions, in addition to a population on Pha‐ngan Island, 150 km offshore from the southern peninsula. Moreover, inclusion of the north‐eastern population renders N. kaouthia paraphyletic in relation to other regional Naja species. The north‐eastern population is therefore probably specifically distinct. Given that these cobras are otherwise undifferentiated based on colour and general appearance to the “typical” cobra type of this region, they would represent a cryptic species. As has been shown in other animal groups from Thailand, it is likely that the geographical characteristics and/or tectonic alteration of these regions have facilitated high levels of population divergence of N. kaouthia in this region. Our study highlights the need for dense sampling of snake populations to reveal their systematics, plan conservation and facilitate anti‐snake venom development.

The parasitic nematode Paracapillaria (Ophidiocapillaria) najae De, 1998, found in the Indian cobra Naja naja is redescribed and re-illustrated in the present study. The monocled cobra Naja kaouthia was discovered to be a new host for this parasite in central Thailand. A comprehensive description extending the morphological and molecular characteristics of the parasites is provided to aid species recognition in future studies. The morphometric characters of 41 parasites collected from 5 cobra specimens are compared with those described in the original studies. Phylogenetic analyses using mitochondrial cytochrome c oxidase subunit 1 and nuclear 18S ribosomal RNA genes were performed to provide novel information on the systematics of P. najae. Similar characteristics were observed in the examined nematode samples, despite being found in different hosts, confirming their identity as P. najae. The molecular genetic results support the species status of P. najae, indicating P. najae is well defined and separated from other related nematode species in the family Capillariidae. Morphological descriptions, genetic sequences, evolutionary relationships among capillariids and new host and distribution records of P. najae are discussed. Paracapillaria najae specimens found in the Thai cobra had some morphological variation, and sexual size dimorphism was also indicated. Paracapillaria najae was found to infect various cobra host species and appeared to be common throughout the Oriental regions, consistent with its hosts' distribution.

The morphological variation, extended distribution, and sequence divergence of a recently described of cobra Naja fuxiShi et al., 2022 captured from mountainous areas in Thailand are evaluated by using molecular and morphological analyses. We investigated the genetic variation and affinities of 72 specimens in the genus Naja by using mitochondrial DNA (cytochrome b and control region) and the nuclear DNA gene, C-mos. Morphological examination was conducted for 33 cobra specimens obtained from the northern, western, and north-eastern regions, and data on their natural history were gathered during field surveys. A high degree of genetic differentiation was shown to exist between the cobras collected from lowlands and those from mountainous areas. N. fuxi occurs in uplands bordering Thailand’s Central Basin, whereas the similar looking N. kaouthia Lesson, 1831 is more or less restricted to the lowlands. All phylogenetic and network analyses supported a distinct clade of N. fuxi from north, west, and, north-east regions. In addition, N. fuxi seems to exhibit a split between the north-eastern population and those from the north and west. The range of N. fuxi probably extends far into the mountainous areas of the neighbouring countries Myanmar, Laos, and Vietnam. Morphologically, N. fuxi in Thailand can be distinguished from all other cobra species in the adjacent Oriental Region. The speciation of cobras in Thailand likely reflects key events in the region’s geographical, climate and environmental history.