Surprising cryptic cavefish diversity in a long-studied karst cave ecosystem of northern Alabama.

Subterranean ecosystems host highly specialized and often cryptic biodiversity, yet even intensively studied landscapes may conceal deeply divergent vertebrate lineages. Here we describe Demogorgonichthys arcanus gen. et sp. nov., a new genus and species of cave-obligate fish discovered in Bobcat Cave, a long-monitored karst system on Redstone Arsenal in northern Alabama, USA. Phylogenetic analyses based on mitochondrial nd2, complete mitochondrial genomes, and the nuclear gene rhodopsin place D. arcanus within Amblyopsidae but reveal deep divergence from all described genera, including extensive lineage-specific degeneration of a vision-related gene. Notably, D. arcanus occurs in syntopy with the Southern Cavefish (Typhlichthys subterraneus) despite lacking a close phylogenetic relationship, providing evidence for multiple independent evolutionary origins of cave adaptation within a single groundwater system. This discovery highlights persistent detection bias in groundwater ecosystems and demonstrates that cryptic vertebrate diversity can persist even in well-characterized environments. Extreme endemism and restriction to a single cave-aquifer system further underscore the vulnerability of subterranean biodiversity and the importance of integrating evolutionary and conservation perspectives.