New cecidospecies of Anoigmaichnus in the cystoporate bryozoan Fistulipora przhidolensis from the upper Pridoli (Silurian) of Saaremaa Island, Estonia

The ichnogenus Anoigmaichnus is redefined as a cecidogenus. A new bioclaustration Anoigmaichnus soervensis Vinn & Ernst csp. nov. has been identified within the cystoporate bryozoan Fistulipora przhidolensis from the upper Pridoli of Saarema Island, Estonia. The bioclaustration associated with this species features cavities with a smooth sheath made of host bryozoan’s skeletal material. Directly below the bioclaustration there is a Trypanites boring. The apertures of this bioclaustration shaft rise above the host’s growth surface, forming a well-developed apertural rim. Ordovician trepostomes typically exhibited up to four Anoigmaichnus bioclaustrations per colony, whereas Silurian cystoporates showed a prevalence up to ten times higher. It is conceivable that host bryozoan exhibited greater tolerance towards A. soervensis csp. nov. compared to other species of Anoigmnaichnus due to its potentially lower virulence. The polychaetes could potentially have been responsible for creating Anoigmaichnus bioclaustrations in Fistulipora.