Histiostoma palustre n. sp. is described. Common characyers of the deutonymph show that H. litorale is the sister species of H. palustre n. sp. As a dreived character, males of H. palustre n. sp. are polymorphic with respect to the shape of the second leg. This leg can be considerably enlarged. Enlarged legs function as a clasping organ in fights with other males for females. A new nomenclature is proposed for dorsal and ventral setae, for ventral apodems of the deutonymph and for the cuticular pattern of the propodosoma shield of the adults. The taxon Hististomatidae is proposed to be monophyletic based on characters mainly of the gnathosaoma. The stem species pattern of the Histiostamatidae is reconstructed.