Castellaniella hirudinis is a gram-negative, rod-shaped, non-spore-forming, bacterium from the genus of Castellaniella which has been isolated from the skin of a juvenile medical leech (Hirudo verbana) in Biebertal in Germany.
Among its neighbouring communities are Weimar an der Lahn in the northeast, Fronhausen in the southeast and in the northwest Gladenbach, all in the Marburg-Biedenkopf district, as well as the town of Lollar, Wettenberg and Biebertal in Gießen district, and Bischoffen in Lahn-Dill district.