<p>The type, size, shape and distribution of nematocysts represent important taxonomic characters that help to identify many hydrozoan species. The Stylasteridae is one of the most species-rich hydroid families. Nevertheless, information about the soft tissue and especially data about the nematocysts are still very scant. Scattered data about nematocysts are available in several taxonomic papers, but unfortunately without the type identification or shape description, this information is not very useful. Therefore, several questions still need answers. What types of nematocysts are present in the stylasterid family? Do nematocysts have a particular distribution in the soft tissue? Could they be considered a useful taxonomic character for the family? Is it possible to hypothesize their functions? In order to answer these questions, we analysed 15 stylasterid species belonging to seven genera. Euryteles, desmonemes, isorhizas and probably also mastigophores were identified. All examined species have euryteles and desmonemes, while isorhizas are recorded in two genera and mastigophores in only one genus. Moreover, the shape of the nematocysts in some species is very distinct. The distribution of nematocysts shows that each species contains, in the coenosarc, all nematocysts of its cnidome, while in the polyps there are only euryteles and desmonemes. Our study showed that in integrating the information about nematocyst type, size, shape and distribution, each species investigated herein has a specific cnidome. Therefore, nematocysts have a taxonomic value for stylasterids and, whenever possible, nematocysts should be included in the species descriptions. Moreover, the possible functions of stylasterid nematocysts are given in relation to their type and distribution.</p
