The karyology study of the Nuttallochiton mirandus showed, comparing this chromosome set with the available chiton karyotypes, differences in both number and morphology as well as an interesting similarity to the fundamental number of the species of genus Acanthochitona (Odierna et al., 2008). The similarity of the karyotypes of N. mirandus and A. crinita (Colombera & Tagliaferri, 1983), which has been demonstrated to be a sister taxon by molecular analysis (Okusu et al., 2003), is particularly interesting. The two species share the same fundamental number and have karyotypes which, on the basis of the number of bi-armed and uni-armed elements, can easily have derived from one another via Robertsonian mutation (Odierna et al. 2008). The results of the study of N. mirandus karyology carried out by Odierna et al. (2008) provided useful information on chiton phylogenesis and the chromosome changes that may have taken place in its course.