Back to the roots, Part 2—Rhopaliophora (Scyphozoa, Cubozoa and Staurozoa) reborn based on early life cycle data

Abstract

The first part of this study focused on the morphology of different early life stages and their further development. This second part of the study demonstrates that the different types of polyps, strobilations/metamorphoses, their products (residues/ephyrae/medusae) and their further development (e.g. gastric system development of ephyrae) explain well the evolutionary development of the Rhopaliophora.

By using the strobilation rates and information on the way morphological characters changed during the process of strobilation/metamorphosis, the strobilation and metamorphosis types were newly defined. Species were allocated to types by the combination of this information. The incomplete metamorphosis in Carybdea xaymacana is re-affirmed as a modified monodisc strobilation according to the newly investigated monodisc strobilation type in carukiid species. Complete metamorphosis is a form derived from the modified monodisc strobilation, as well as the metamorphosis type observed in Staurozoa.

A clear separation of “Rhizostomeae” into two paraphyletic groups (Kolpophorae and Rhizostomatidea) and the polyphyly of Semaeostomeae is demonstrated. The results lead to a new and reorganised taxonomic system for the class Scyphozoa, which once more includes Cubomedusae and Stauromedusae. Scyphozoa now comprises two subclasses: Coronamedusae and Discomedusae. The latter subclass includes the newly-created infraclasses Pelagimedusae and Centrifugalia. Two new superorders, each containing two new orders (Stipeslongida: Sanderiida, Metamorphida; Opposita: Circulumcanalida, Cyaneida), are contained within the Centrifugalia.

The new order Circulumcanalida now contains two newly erected suborders: Antherhizostomatida and Phacellophorida. The former new suborder contains the newly erected infraorders Kolpophorae and Centripetalida. The family Sanderiidae was further erected within the new order Sanderiida.