The potential role of the sphaeractinomyxon collective group (Cnidaria, Myxozoa) in the life cycle of mugiliform-infecting myxobolids, with the morphological and molecular description of three new types from the oligochaete Tubificoides insularis.

Three new types of sphaeractinomyxon (Cnidaria, Myxozoa) are described from the coelomic cavity of the marine oligochaete Tubificoides insularis, collected from the Alvor estuary, Algarve, Portugal. Another known type is also registered from this location and host: Sphaeractinomyxon type 10 of Rangel et al. (2016), which was originally described from the marine oligochaete Tubificoides pseudogaster in the Aveiro estuary, Portugal. Phylogenetic analysis revealed the case isolates and all other available SSU rRNA sequences of sphaeractinomyxon clustering within a clade containing Myxobolus spp. that infect mullets, thus suggesting that this collective group plays a role in the life cycle of mugiliform-infecting myxobolids. Also clustering within this clade were all types of tetraspora and endocapsa, calling into question the distinctiveness of these collective groups. Acknowledging a previous work showing that the pansporocysts of sphaeractinomyxon produce a variable number of actinospores, we suggest that the tetraspora collective group be deemed invalid and its types transferred to sphaeractinomyxon. In turn, endocapsa requires validation through the description of new types truly differentiating them from sphaeractinomyxon.