Tetractinomyxon stages genetically consistent with Sphaerospora dicentrarchi (Myxozoa: Sphaerosporidae) found in Capitella sp (Polychaeta: Capitellidae) suggest potential role of marine polychaetes in parasite's life cycle

Known life cycles of myxosporean parasites have two hosts, but very few life cycles have been disclosed, especially in the marine environment. Sphaerospora dicentrarchi Sitja-Bobadilla and alvarez-Pellitero, 1992 is a systemic parasite from the European seabass, Dicentrarchus labrax (Linnaeus, 1758), a highly valuable commercial fish. It affects its health, leading to aquaculture production losses. During 2013 and 2014, an actinospore survey was conducted in a total of 5942 annelids collected from a fish farm in Algarve and from the Aveiro Estuary, in Portugal. A new tetractinomyxon actinospore was found in a capitellid polychaete, belonging to the genera Capitella collected at the fish farm. The tetractinomyxons were pyriform measuring 111 +/- 07 mu m in length and 72 +/- 04 mu m in width, and presented three rounded polar capsules measuring 24 +/- 03 mu m in diameter. The molecular analysis of the 18S rRNA gene sequences from the tetractinomyxons revealed a similarity of 100% with the DNA sequences deposited in the GenBank from S. dicentrarchi myxospores collected from the European seabass and the spotted seabass in the same fish farm and 999% similarity with the DNA sequence obtained from the myxospores found infecting the European seabass in the Aveiro Estuary. Therefore, the new tetractinomyxons are inferred to represent the actinospore phase of the S. dicentrarchi life cycle.