Description of new types of sphaeractinomyxon actinospores (Myxozoa: Myxosporea) from marine tubificid oligochaetes, with a discussion on the validity of the tetraspora and the endocapsa as actinospore collective group names.

Ten new types of sphaeractinomyxon actinospores are morphologically and molecularly described from the coelomic cavity of two marine oligochaete hosts, Limnodriloides agnes (Hrabě, 1967) and Tubificoides pseudogaster (Dahl, 1960), from Aveiro estuary, Portugal. The smallest sphaeractinomyxon type measured 17 μm (length) × 19 μm (width) × 19 μm (apical diameter), whereas the largest type measured 61 μm × 76 μm × 80 μm. While considering the 10 types of sphaeractinomyxon, it was found that the number of spores developing inside pansporocysts varied between 1, 2, 4, and 8. The total prevalence of infection was of 19 % for the two host species, with a maximum recorded for spring and summer (25-26 %). While considering each type of sphaeractinomyxon individually, it was found that the prevalence values ranged between 0.3 and 1.7 %. All described sphaeractinomyxons were most similar to Myxobolus species. The validity of the tetraspora and endocapsa collective group names is discussed.