Infestation of the branchiobdellidan, Xironogiton victoriensis (Anellida: Clitellata), on the signal crayfish (Pacifastacus leniusculus) from Auenbachl Creek, Alto Adige /Südtirol, Italy.

Live specimens of the North American signal crayfish, Pacifastacus leniusculus (Dana 1852), were collected from Auenbachl Creek, near Brunico, Province of Bolzano, Italy. Each crayfish carried, on average, 1500 branchiobdellidans of the species Xironogiton victoriensis (Gelder and Hall 1990). A brief description of some of the main morphological features is given, including the variation in the dental formula: 4/4 to 5/5. The presence of branchiobdellidans is discussed in relation to infestation of other organisms on autochthonous and allochthonous freshwater crayfishes reported in Italy.