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 Stenostomum sphagnetorum against the predatory ciliate, Coleps hirtus. Focusing on the role of the glandular secretions produced by S. sphagnetorum, the research demonstrates that the flatworm secretes mucus that acts as a barrier, disrupting predator attack. In particular, we show that: (1) S. sphagnetorum specimens artificially deprived of glandular secretions are significantly more susceptible to predation by C. hirtus than untreated specimens; (2) the secretion-deprived organisms consistently exhibit a significantly greater sensitivity to the main toxins employed by C. hirtus 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.