Aenigmachannidae, a new family of snakehead fishes (Teleostei: Channoidei) from subterranean waters of South India

Abstract

Pronounced organism-wide morphological stasis in evolution has resulted in taxa with unusually high numbers of primitive characters. These ‘living fossils’ hold a prominent role for our understanding of the diversification of the group in question. Here we provide the first detailed osteological analysis of Aenigmachanna gollum based on high-resolution nano-CT scans and one cleared and stained specimen of this recently described snakehead fish from subterranean waters of Kerala in South India. In addition to a number of derived and unique features, Aenigmachanna has several characters that exhibit putatively primitive conditions not encountered in the family Channidae. Our morphological analysis provides evidence for the phylogenetic position of Aenigmachanna as the sister group to Channidae. Molecular analyses further emphasize the uniqueness of Aenigmachanna and indicate that it is a separate lineage of snakeheads, estimated to have split from its sister group at least 34 or 109 million years ago depending on the fossil calibration employed. This may indicate that Aenigmachanna is a Gondwanan lineage, which has survived break-up of the supercontinent, with India separating from Africa at around 120 mya. The surprising morphological disparity of Aenigmachanna from members of the Channidae lead us to erect a new family of snakehead fishes, Aenigmachannidae, sister group to Channidae, to accommodate these unique snakehead fishes.

Evolution in the dark: Unexpected genetic diversity and morphological stasis in the blind, aquifer-dwelling catfish Horaglanis

“…We suspect that morphological stasis in Horaglanis may be the result of a combination of several of these factors. The small pore size of the lateritic rocks in the aquifers restricts access to this habitat for other subterranean predators such as Aenigmachanna (Britz et al 2020), resulting in a predator-free environment for Horaglanis, thus severely limiting interspecific competition. The low number of just 25 to 30 comparatively large eggs in Horaglanis (Mercy 1981) may be a response to living in a nutrient poor habitat.…”

“…This is especially true for bony fishes, with 289 valid species currently known from subterranean aquatic habitats on every continent except Antarctica (Proudlove 2022). These include some spectacular radiations of cave-adapted species , as well as lineages of 'living fossils' (Britz et al 2020). These unusual fish species have been aptly called the 'wrecks of ancient life' (Darwin 1809(Darwin -1822 and 'ghosts in the water' (Niemiller et al 2019); many of them enjoy unusual scientific names (e.g., Satan eurystomus Hubbs & Bailey, Aenigmachanna gollum Britz, Anoop, Dahanukar & Raghavan), or have emerged as laboratory models (e.g., Astyanax mexicanus (de Filippi)) for understanding evolution, development, behaviour, and human health (Krishnan and Rohner 2017;McGaugh et al 2020).…”

Diversifying on the Ark: multiple new endemic lineages of dwarf geckos from the Western Ghats provide insights into the systematics and biogeography of South Asian <i>Cnemaspis</i> (Reptilia: Squamata)

“…It has been suggested that significant parts of the WG will be urbanized by 2030 due to population expansion and development ( Seto et al, 2012 ). The recent discoveries of new evolutionarily distinct lineages from the WG highlight the biogeographic and evolutionary significance of this region as well as the importance of sampling strategies to detect endemic lineages while conducting broad-level phylogenetic studies ( Britz et al, 2020 ; Chaitanya et al, 2019 ; Dinesh et al, 2020 ; Mallik et al, 2019 ; Pal et al, 2018 ; Robin et al, 2017 ; Vijayakumar et al, 2019 ). The recognition of 10 new morphologically distinct and geographically isolated species of Cnemaspis from the SWG also highlights our lack of knowledge regarding the immense diversity of this region and its potential to harbor more unknown species.…”

The world’s largest cave fish from Meghalaya, Northeast India, is a new species, Neolissochilus pnar (Cyprinidae, Torinae)

“…A number of these species are evolutionary relics of an ancient fauna, often with long-term isolation in these high-stress environments (Gibert and Deharveng 2002). Such evolutionarily relictual lineages include among others, the Aenigmachannidae -a "living fossil" with a putative Jurassic origin (Britz et al 2020), the enigmatic Kryptoglanidae (Britz et al 2014), the cistern catfish Phreatobius (Muriel-Cunha and de Pinna 2005), and the blind aquifer-dwelling Horaglanis (Raghavan et al 2023). However, the large majority of cavefishes represent "young" lineages that have much more recently invaded subterranean habitats -examples include the European cave loach, Barbatula sp., and the Mexican blind swamp eel, Ophisternon infernale (Behrmann-Godel et al 2017;Mar-Silva et al 2022).…”