Anoigmaichnus

Trace fossil

Anoigmaichnus is an ichnogenus of bioclaustrations. Anoigmaichnus includes shafts perpendicular to their hosts' growth surfaces or tilted (up to 45°); conical to cylindrical; circular to oval cross-sections; lacking separate wall. Their apertures are elevated above their hosts' growth surfaces, forming short chimney-like structures. Anoigmaichnus is the world's earliest known macroscopic endobiotic symbiont and it may have been a parasite. It occurs in the Middle Ordovician bryozoans of Osmussaar Island, Estonia.

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