An enigmatic filiform organism in the epicardium cavity of a new polycitorid ascidian

In several samples of the ascidian Eudistoma hospitale n.sp. collected in the western Pacific Ocean and in South Africa, a filiform organism was found implanted on the heart tissue. It is rolled in balls, occupies a large part of the ascidian abdominal cavity, and reaches such a length that it bursts through the branchial sac and finally comes out at the colony surface with a free tip. Present in all zooids and in larvae, always single, this filament remains of an unknown nature, despite all cytochemical and microanalytical methods used to characterize it. This kind of organism has never been recorded in any other ascidian.