The jellyfish Rhizostoma luteum (Quoy & Gaimard, 1827): not such a rare species after all

Rhizostoma luteum was first described in 1827 by Quoy and Gaimard under the name Orythia lutea, based on nine specimens collected from the Strait of Gibraltar (southern Iberian Peninsula). After 60 years of no scientific records existing for this species, in 2013, a phylogenetic analysis confirmed that R. luteum differed from Rhizostoma pulmo and Rhizostoma octopus. In the present study, we report historical and recent records of living and stranded specimens of R. luteum since 1998. We reviewed historical accounts and photographic and videographic materials taken by citizens from the northeastern Atlantic Ocean and the Alboran Sea. Because of its similarity with the closely related Mediterranean R. pulmo, R. luteum was frequently misidentified in the Alboran Sea and, likewise, with another medusa from the order Rhizostomeae, Catostylus tagi, in the adjacent Atlantic Ocean coastal regions in the last two decades. The results of this investigation confirm the existence of the scyphomedusa R. luteum in the coastal waters of the west and south coasts of the Iberian Peninsula and west and north shores of Africa. Through a citizen science initiative and our own observations, we were able to confirm more than 150 observations of R. luteum over the past 17 years, demonstrating that this medusa is not such a rare species after all.