cnidocils

Cnidocils are slender, hair-like sensory projections found on cnidocytes, the stinging cells of cnidarians such as jellyfish, sea anemones, and corals. Each cnidocyte contains a capsule, the cnidocyst, which houses a coiled tubule. The cnidocil is typically described as a modified cilium or flagellum at the apex of the cnidocyte and acts as a mechanosensory trigger for discharge.

When the cnidocil is stimulated by mechanical contact or certain chemical cues, a rapid signal transduction cascade is initiated. This leads to the explosive discharge of the nematocyst: the capsule everts under high pressure, ejecting the tubule, which can penetrate tissue and deliver venom or toxins to prey or to deter predators. The discharge occurs very quickly, making it one of the fastest known cellular processes.

The cnidocil’s primary role is in feeding and defense. It helps cnidarians capture prey by delivering toxins and immobilizing targets, and it also serves to deter potential threats. The sensitivity and response of cnidocils can vary among species and developmental stages, and they may respond to both mechanical and chemical stimuli, often enhancing prey capture efficiency.

Overall, cnidocils are a key component of the cnidocyte apparatus, enabling rapid, targeted nematocyst discharge that underpins the feeding ecology and defensive strategies of cnidarians.