Hydroid-serpulid symbiosis in the Mesozoic and Tertiary

Several species of Mesozoic and Tertiary serpulids from Europe and the Middle East were infested by a colonial organism which is preserved as the mould of a stolonal network with polyp chambers buried in the peripheral zone of the calcareous tube. The polyp chambers open to the outer surface of the tube through small, usually semicircular apertures. The mould is the result of incorporation of the organism into the worm tube during calcification by the serpulid: it is not a boring. The organism is interpreted as a hydroid or group of related hydroids which lived commensally or possibly mutualistically with the serpulids. This hydroid-serpulid symbiosis is compared with the living symbiosis between the hydroids of Proboscidactyla and certain species of sabellid polychaetes. The name of the fossil symbiont is Protulophila gestroi Rovereto.