Mucus Secretion as a Defensive Mechanism in the Freshwater Flatworm Stenostomum sphagnetorum Against the Ciliate Predator Coleps hirtus

This study investigates the defensive mechanisms employed by the freshwater flatworm <i>Stenostomum sphagnetorum</i> against the predatory ciliate, <i>Coleps hirtus</i>. Focusing on the role of the glandular secretions produced by <i>S. sphagnetorum</i>, the research demonstrates that the flatworm secretes mucus that acts as a barrier, disrupting predator attack. In particular, we show that: (1) <i>S. sphagnetorum</i> specimens artificially deprived of glandular secretions are significantly more susceptible to predation by <i>C. hirtus</i> than untreated specimens; (2) the secretion-deprived organisms consistently exhibit a significantly greater sensitivity to the main toxins employed by <i>C. hirtus</i> for predation, relative to untreated counterparts; (3) the characterization of the glandular secretion indicates that the mucus contains both neutral and acidic glycosaminoglycans, along with protein components, suggesting a complex chemical composition that may contribute to its protective function.