Interpretation of synapomorphies of spermatozoa, placed on a phylogeny of the Polyopisthocotylea. Left: Character changes as postulated in Boeger & Kritsky (2001) [14]. The taxon defined by the character “presence of lateral microtubules in principal region of spermatozoon” is the Polyopisthocotylea as a whole. Right: Character changes as evidenced by present study. The taxon defined by the character “presence of lateral microtubules in principal region of spermatozoon” is restricted to the Mazocraeidea.