spirocyst

A spirocyst is a type of cnidocyte, a specialized stinging cell found in cnidarians such as sea anemones and jellyfish. Spirocysts are primarily found in the tentacles and oral arms of these animals. Unlike cnidocytes that contain nematocysts, spirocysts do not possess a coiled, barbed thread. Instead, they discharge a sticky, non-barbed filament.

When a spirocyst is triggered, usually by physical or chemical stimuli, the filament rapidly everts and adheres to the surface of a potential prey item or a predator. This sticky secretion helps to immobilize small prey, allowing the cnidarian to manipulate it towards its mouth for ingestion. The filament also plays a role in defense, deterring predators by adhering to them.

The function of spirocysts is distinct from nematocysts, which inject venom. Spirocysts are involved in adhesion rather than envenomation. While both are types of stinging cells, their mechanisms and primary roles differ. The exact composition and adhesive properties of the spirocyst filament are still areas of research. Spirocysts are a key component of the feeding and defense apparatus of many cnidarian species.