Dual-phase adhesive secretion in the stalked barnacle Capitulum mitella

Barnacles are a highly diverse group that includes sessile, stalked, and parasitic forms, all capable of adhering strongly to wet surfaces. While acorn barnacle adhesion has been well studied, the mechanisms in stalked barnacles remain poorly understood. Herein, the adhesive of Capitulum mitella is investigated, revealing a two-phase secretion: a fluid-phase mixture extruded through glandular structures and a solidified adhesive with distinct lamellar architecture. The outer layers of adhesive can resist environmental stress, while the inner fibrous network contributes to cohesion and viscoelasticity. These components differ markedly in morphology and chemical composition. Raman spectroscopy, FTIR, and thioflavin T staining confirm the absence of amyloid-like β-sheet structures, in contrast to previously reported amyloid-based architectures in acorn barnacle adhesives. The results highlight species-specific adhesive strategies in stalked barnacles and offer insights relevant to the development of bioinspired adhesives and antifouling technologies.