A histological approach to investigate the decay of gastropod internal organs

Molluscs are important components in both past and modern ecosystems. Understanding their evolutionary history relies on accurately interpreting their past morphologies as preserved in the fossil record. However, organisms typically undergo decay before geological processes intervene to stabilise parts of their anatomy as fossils. To assess the impact of decay on our understanding of ancient morphologies, decay experiments have been conducted in controlled laboratory settings. Such experiments have rarely been applied to gastropods, as their mineralised shell covers internal organs, making direct observation of decaying anatomies experimentally challenging. Here, we conducted decay experiments on 55 snails over 10 days, using histological sections to observe internal morphological changes over time. Our results show that most of the organs we monitored decay uniformly, except for the hepatopancreas, which decomposes more slowly than the rest. Importantly, decay proceeded faster on the outside than on the inside of the hepatopancreas, suggesting that digestive enzymes of microbiota in gastropods may not be as efficient at tissue degradation as those in the digestive systems of other bilaterians.