Symbiosis plays a key role in the functioning of ecosystems and in the evolution of organisms; however, direct evidence of such relationships in the fossil record is rare. The Jurassic seas of the Polish Basin nearly 170 million years ago concealed complex and exceptionally close symbiotic interactions. Six years after the publication of the first studies on the symbiosis between sessile polychaetes (serpulids) and hydroids using micro–computed tomography, detailed analyses have enabled a far more in-depth interpretation of the mechanisms underlying this interaction.
Dr Jakub Słowiński and his collaborators analyzed exceptionally well-preserved fossils of Jurassic colonies of the hydroid Protulophila gestroi living within the carbonate skeleton of the serpulid Propomatoceros lumbricalis, dating to approximately 165–170 million years ago. The high resolution of microtomographic scans made it possible to reconstruct the internal structure of the colonies in three dimensions. The study included specimens derived from several different palaeoenvironments of the Jurassic Polish Basin.
The analyses showed that the interaction between host and symbiont was far more complex than previously assumed. The development of the hydroid colonies was clearly controlled by the biomineralization process of the serpulids. The manner and rate of formation of the calcareous tube directly influenced the morphology and depth of incorporation of the colonies within the host’s skeleton. At the same time, some colonies exhibited considerable morphological variability even within the same serpulid specimen and environment, suggesting a strong influence of local environmental conditions such as hydrodynamics or food availability.
The research provides an exceptionally detailed insight into interactions between symbiotic organisms in the Mesozoic Era and suggests a strong influence of physiological dependence. It also demonstrates that modern imaging techniques open up new possibilities for studying ecological relationships preserved in fossils, allowing non-invasive and highly precise reconstructions of interactions that occurred between organisms many millions of years ago.
The research was carried out as part of the PRELUDIUM-21 research project led by Dr Jakub Słowiński, entitled “Phylogenetic and palaeoecological reconstruction of symbiotic relationships between serpulids and hydroids using micro–computed tomography imaging methods,” funded by the National Science Centre (Narodowe Centrum Nauki). The results were published in the British journal Palaeontology.
Słowiński, J., Duda, P., Nawrot, R. & Zatoń, M. 2026. Micro‐CT reveals host‐controlled symbiosis of the Jurassic serpulid–hydroid association. Palaeontology, 69 (3), e70070; doi: doi.org/10.1111/pala.70070.
