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Spermiogenesis in Scaphiostomum palaearcticum begins with the formation of a zone of differentiation, which comprises striated rootlets associated with the two centrioles and an intercentriolar body in-between. It is characterised by an asynchronic flagellar rotation and subsequent proximo-distal fusion with a median cytoplasmic process. The migration of the nucleus toward the median cytoplasmic process before its fusion with the free flagella is also described. However, in the case of S. palaearcticum, the mitochondrion migrates toward the median cytoplasmic process before the fusion of the second axoneme. Attachment zones are also formed before the fusion of the axonemes with the median cytoplasmic process. The mature spermatozoon of S. palaearcticum is filiform and tapered at both ends and presents all the features found in the Digenea gamete: two axonemes, mitochondrion, nucleus and two bundles of parallel cortical microtubules. Nevertheless, certain features allow us to distinguish S. palaearcticum from other digenetic trematodes.