New advances in jellyfish anatomy: the benefits of endocasts and X-ray microtomography in the investigation of the gastrovascular system of Cotylorhiza tuberculata (Scyphozoa; Rhizostomeae; Cepheidae).

Historically, research on jellyfish anatomy has been viewed as secondary in importance and has not benefited from technical advances that could improve the quality of the results when compared to other disciplines. The most notable example is the anatomical research on jellyfish, which has been done using conventional methods for many years. Thus far, recent studies have shown that X-ray microtomography (µCT) and resin endocasts can yield outputs with remarkably high detail quality. The application of a similar protocol to Cotylorhiza tuberculata has allowed us to redescribe the anatomy of this species' gastrovascular system, providing numerous additional details, among them the double constricted canal structure present in the oral arms, which was absent in previous descriptions. Additionally, functional anatomy experiments have revealed a double circulation system within these canals, featuring specialized oral arms' openings for intake and outflow, as previously observed in Rhizostoma pulmo. These findings challenge the theory of a simple digestive system in scyphozoans featuring openings that acts both as mouths and anuses. Given the genetic distance between Cotylorhiza tuberculata and Rhizostoma pulmo, which belong to different suborders (Kolpophorae and Dactyliophorae, respectively), we propose that this complex gastrovascular circulation pattern may be more widespread among the Rhizostomeae.