Abstract. – Following an introductory presentation of the problems raised by the examination of the morphological characters according to the phylogenetic systematics, a detailed analysis of the morphological characters of the family Trichoniscidae within the context of the characters of the representatives of the suborder Oniscidea, is achieved, based on the author’s personal data and an examination of the literature. Starting from this analysis we argue once more the author’s conclusions concerning controversial issues: the monophyly of the terrestrial isopods; the dichotomy of the suborder Oniscidea; the dichotomy of the infraorder Ligiamorpha; the dichotomy of the monophylum Orthogonopoda