First record of aurantiactinomyxon and saccimyxon type actinosporean stages of fish ınfecting myxozoan parasites (cnidaria) through morphological and molecular ıdentifications in Türkiye

The present study investigates annelid hosts of the actinosporean stages of myxozoan parasites in freshwater and estuarine habitats within a stream system that flows into the Sea of Marmara, Türkiye.Following a comprehensive 12-month sampling period that included 1,781 specimens, Limnodrilus hoffmeisteri (Oligochaeta, n=1078) was the dominant species at freshwater stations, whereas Hediste astae (Polychaeta, n=703) dominated in downstream reaches.Specimens underwent parasitological examination, and three distinct myxozoan actinospore types were identified: one aurantiactinomyxon type in L. hoffmeisteri and two saccimyxon types (I and II) in H. astae.The overall prevalence was 0.09% for the aurantiactinomyxon type, 0.4% for saccimyxon type I, and 0.7% for saccimyxon type II.Physicochemical assessments showed that salinity was the primary factor driving population differentiation among annelid populations at the sampling localities.Furthermore, water temperature is the primary factor determining the seasonal occurrence of actinospores. Molecular analysis of the 18S rDNA region established robust evolutionary links between saccimyxon types I and Ellipsomyxa gobii, and between saccimyxon types II andEllipsomyxa mugilis, respectively.Thus, this study is the first record of the genus Ellipsomyxa along the Turkish coasts and in the eastern Mediterranean, including E. gobii and E. mugilis.Additionally, it constitutes the second record of E. gobii since its original description from Denmark.This study is the first report of actinosporean stages of fishinfecting myxozoan parasites in Türkiye and provides critical insights into how environmental parameters shape host-parasite specificity in estuarine ecosystems, thereby contributing to current knowledge of myxozoan life cycles.