Colloblasts

Colloblasts are specialized epidermal secretory cells unique to the phylum Ctenophora (comb jellies). They occur on the surface of the tentacles, and in some species on smaller projections called tentilla, where they form an adhesive region used to capture prey. Each colloblast cell contains granules that release a sticky substance by exocytosis when stimulated by contact with prey. The adhesive is a protein- and polysaccharide-rich mucus; its exact chemical composition is not fully known, but proteinaceous components and glycopolymers are implicated. The discharge is generally thought to be mechanically triggered by prey contact, and colloblasts do not inject toxins as cnidarians do.

In feeding, small zooplankton brush against the adhesive tentacles; upon activation, the prey adheres to the tentacle surface. The ctenophore then uses muscular action and tentillar movement to bring the prey toward its mouth. Adhesive strength and duration vary with species and environmental conditions, and adhesion can be temporary, allowing prey to be released if necessary.

Ecological and research notes: Colloblasts enable efficient capture of small, mobile prey in marine environments and represent a distinct form of biological adhesion. Because they rely on attachment rather than venom, colloblasts are of interest in studies of bioadhesion, cell–substrate interactions, and the evolution of feeding mechanisms in early-diverging animal lineages.