Rhizostoma luteum; a large jellyfish to be rediscovered

Abstract

Until summer 2012 Rhizostoma luteum was a forgotten species, and even some scientist doubted its occurrence, believing it might be a young Rhizostoma pulmo or a local variation. The first mention of this large Scyphozoa was by Quoy and Gaimard in 1827 from the Strait of Gibraltar (southern Iberian Peninsula). We describe for the first time, the life cycle of this jellyfish and compare it with early life history stages of its sibling species Rhizostoma pulmo and Rhizostoma octopus. We observed only one asexual reproduction mode, which is employed for propagation, consisting of podocyst formation with excystment, subsequent development of scyphistoma, strobilation and liberation of viable ephyra. Furthermore, the development of ephyra to metaephyra was photodocumented, reaching the metaephyra stage in approximately 21-25 days. The life cycle of R. luteum resembles that of its congeners, with the distinction that it has the unique feature of being a brooding species (internal fertilisation with subsequent release of planulae) and under the conditions tested, the predominantly strobilation type observed was monodisc, and not polydisc as with the other two species in the genus Rhizostoma. Thus, to better understand its ecological roles, it is essential to study its life cycle.