Early symbiotic rugosan endobionts in stromatoporoids from the Rhuddanian of Estonia (Baltica)

Abstract

The earliest known symbiotic rugosan endobionts occur in stromatoporoids from the early Rhuddanian of Estonia. The stromatoporoid Ecclimadictyon nikitini from the Tamsalu Formation contains the rugosan Donacophyllum middendorffii endobiont. A stromatoporoid Clathrodictyon boreale from the Varbola Formation contains Streptelasma estonica and Bodophyllum sp. endobionts. There are up to three endobiotic rugosans per stromatoporoid host. Stromatoporoid hosts were beneficial for symbiotic rugosans as elevated substrates on a seafloor that offered a higher tier for feeding; they also offered enhanced substrate stability. Stromatoporoids of the end‐Ordovician mass‐extinction recovery fauna hosted a diverse fauna of symbiotic endobionts. There were few if any negative effects of this mass extinction on the symbiotic endobionts.

Sclerobiosis: A Term for Colonization of Marine Hard Substrates

“…They are overgrowth and intergrowth interactions between sclerobiont-sclerobiont and sclerobiont-hard living substrate (e.g., encrusting organisms with hard skeletons or borers colonizing a skeletonized host substrate) (Taylor & Wilson, 2003). Colonizers often intergrow with their living substrates, such as in case of rugosans in corals (Vinn et al, 2017a), bryozoans (Vinn et al, 2016(Vinn et al, , 2017b and stromatoporoids (Vinn et al, 2015;Vinn, 2016;Vinn & Toom, 2017). Bioclaustrations are common in corals (Tapanila, 2005;Mõtus & Vinn, 2009;Wilson et al, 2014), bryozoans (Vinn et al, 2014 and stromatoporoids (Vinn et al, 2013).…”