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

The lateritic aquifers of the southern Indian state Kerala harbour a unique assemblage enigmatic stygobitic fishes which are encountered very rarely, only when they surface during digging and cleaning homestead wells. Here, we focus on one most unusual members this group, catfish Horaglanis , genus rarely-collected, tiny, blind, pigment less, strictly aquifer-residing species. A six-year exploratory citizen-science backed survey supported by molecular phylogenetic analysis reveals novel insights into diversity, distribution population structure . is characterized high levels intraspecific interspecific genetic divergence, with phylogenetically distinct species recovered above 7.0% genetic-distance threshold in mitochondrial cytochrome oxidase subunit 1 gene. Contrasting deep however, remarkable stasis external morphology. We identify describe new cryptic species, populi lineage that sister group all currently known All four represented multiple haplotypes. Mismatch populations have not experienced recent expansions.