Tentilla

Tentilla are small lateral branches along the tentacles of certain hydrozoans, especially siphonophores. These structures increase the effective surface area for prey capture and contain one or more nematocyst-bearing units.

Each tentillum is a short, stalked projection on a tentacle, bearing a battery of cnidocytes (nematocysts) that can discharge onto prey. Contact is detected by specialized sensory hairs (cnidocils) on the tentillum. The internal arrangement and morphology vary by species.

In feeding, tentilla cooperate to immobilize and enmesh prey. When triggered, the nematocysts discharge, injecting toxins and sometimes entangling the prey, which is then transported to the gastrozooids for digestion.

Tentilla are characteristic of siphonophores and some colonial hydrozoans. The number, size, and arrangement of tentilla on a tentacle are used in species descriptions and classification.