Leslie Harris le 21/05/19
Pardon me for the correction but it is not a Myxicola. Members of that genus create gelatinous tubes, very soft, translucent, and shapeless. They look like dirty jelly and it seems that nothing will grow on them. This tube looks round and is overgrown. I don't think the identification can go past family Sabellidae.
Guillaume TOURNEMOULI le 15/05/19
Merci beaucoup François...cela semble correspondre.
Bonne soirée :-)