C. nemoralis also secretes two different kinds of protective mucus when disturbed. One is a sticky yellow mucus similar to that produced by certain mollusks that is highly resistant to breakage or tearing. The other is a bubbly substance scientists believe is secreted to smother small predators and/or wash them out of the shell.

The researchers analyzed all five types of mucus using various techniques, including proteomics, X-ray fluorescence, X-ray diffraction, cryoscanning electron microscopy, and liquid chromatography.  They found that all five kinds of mucus share a similar protein composition and that collagen IV is the main structural component. It’s the different quantities of protein and the addition of amorphous calcium carbonate (ACC) that determine a given mucus’s distinct mechanical properties. The two defensive kinds of mucus had the highest number of proteins.

Those results “indicate that these proteins are used to tune the degree of cross-linking and therefore their network density, which has an immediate effect on their mechanical properties,” the authors concluded. “Each mucus type shows a distinct and complex hierarchical structure that is influenced by the processing of the mucus material.”

Furthermore, calcium “is actively secreted together with the mucus, serving as an ion source for cross-linking or a mineral precursor for reinforcement.”

Science, 2026. DOI: 10.1126/science.adx7367 (About DOIs).