Syn vivo encrustation of Porambonites Pander, 1830 (Brachiopoda) by craniid brachiopods in the Late Ordovician of Estonia

Two new brachiopod–brachiopod symbiotic overgrowths have been discovered from the Kukruse Regional Stage (Sandbian, Ordovician) of Estonia. Both the Philhedra rivulosa–Porambonites sp. and the Petrocrania sp.–Porambonites sp. overgrowths were beneficial to the encrusting craniid and might have been slightly harmful to the host brachiopod. The craniids could have been facultative kleptoparasites. Our data show that craniids significantly preferred the smooth shells of Porambonites sp. over the coarsely ribbed shells of Platystrophia sp. and the moderately ribbed shells of Cyrtonotella sp. and Glossorthis sp. This suggests that, at least against craniids, having strong ribs could have been a successful antifouling strategy.