A microendemic fly bound to a fragile ecosystem

Paracoenia beckeri (Kuntze 1897) (Diptera: Ephydridae), an endemic ephydrid restricted to the travertine basin of the Acque Albule (Tivoli, central Italy), is here newly documented through an integrative study combining morphology, barcoding, and ecological observations. We provide an updated and comprehensive redescription of the species with lectotype designation, including adult characters, male terminalia, and—illustrated for the first time—its larval and pupal stages. A detailed comparison with the sympatric congener Paracoenia fumosa (Stenhammar 1844) clarifies their taxonomic boundaries, revealing discrete morphological and ecological differences supported by COI barcode divergence. Field observations across the few remaining sulfurous springs show that P. beckeri is narrowly associated with thermal, CO2-rich microhabitats, whereas P. fumosa occupies adjacent but ecologically distinct stagnant waters. This microhabitat partitioning, coupled with limited genetic separation, suggests a possible case of recent sympatric diversification within Paracoenia. We emphasize the vulnerability of the Acque Albule system, where quarrying, groundwater depletion, and unregulated land use threaten the persistence of suitable habitats. Proper management of abandoned flooded quarries and other anthropogenic wetlands may offer an effective strategy to safeguard this and other species adapted to thermal-sulfurous environments.