The jellyfish order Coronatae is generally known as being composed of deep-sea species, although part of its diversity also occurs in shallow waters. Some species of the genus Nausithoe Kölliker, 1853 (Nausithoidae, Coronatae) were described more than 100 years ago and have never been observed again. As a result, their morphological features cannot be well-reviewed due to the near absence of original vouchers and other specimens for comparative inspection. Most of the 22 presently accepted Nausithoe species have a typical scyphozoan metagenetic life cycle, consisting of alternating polyp and medusa generations. Similarity of the polyps within the genus makes it necessary to study the medusa stage for taxonomy. We explored more than 600 specimens of the genus, questioning the feasibility of using some characters of the medusa stage to identify species and filling gaps in knowledge of diversity and species distributions. Morphological features were observed on preserved and live Nausithoe specimens (polyp and medusa), and genetic information of live specimens was obtained (18S, 28S, and COI). By comparing these data with original descriptions and previous genetic information available, we were able to validate eighteen species and add new localities for some of them.