Symbiotic worms in biostromal stromatoporoids from the Ludfordian (Late Silurian) of Saaremaa, Estonia

Numerous tiny curved to slightly sinuous subvertical tubicolous bioclaustrations occur in stromatoporoids from the Katri cliff biostrome. About 77.8% (N¼18) of Katri biostrome stromatoporoids contained worm endobionts. Chaetosalpinx sibiriensis occurs in Plectostroma scaniense, Petridiostroma convictum and “Stromatopora” bekkeri/Parallelostroma typicum. Helicosalpinx concoenatus occurs in P. scaniense. The distribution of C. sibiriensis is thus not restricted to tabulate corals because it also occurs in stromatoporoids. H. concoenatus was not endemic to North America as it also occurs in the Late Silurian of Baltica.