Nematocysts play an important role in capturing prey; it was suggested that the feeding ecology of animals may result in cnidome variations. We examined nematocysts of polyps and medusae of Aurelia sp. 8 from the Northern Adriatic to detect differences/similarities in cnidome and habitats, and the results show that potential prey of these two phases of the life cycle are very different. Our observations on the nematocysts isolated from the marginal tentacles and oral arms of medusa have shown the presence of four types of nematocysts (in order of decreasing abundance): heterotrichous microbasic eurytele; atrichous isorhiza haploneme; heterotrichous isorhiza haploneme; heterothricous microbasic mastigophore (typeAI) and (A typeII). This last type is very rare (with a rel. freq. << 0.1%), and unexpected. In the polyps (tentacular crown and column) were found three types of nematocysts (in order of decreasing abundance): heterotrichous isorhiza haploneme; heterotrichous microbasic eurytele; atrichous isorhiza haploneme. The atrichous type is localized, being rare-absent in the tentacles, common in the peristomial area and in the column. Prey preferences of northern Adriatic Aurelia polyps and medusae are largely unknown. We attempted to elucidate their dietary habits using available information about stable carbon and nitrogen isotope ratios.
