cnida

Cnida is a term used in biology, specifically in the study of cnidarians, to refer to specialized stinging organelles found in the cells of these animals. Cnidarians include well-known groups like jellyfish, corals, sea anemones, and hydras. The cnida is housed within a specific type of cell called a cnidocyte, which is abundant in the tentacles and other external surfaces of these organisms.

The primary function of cnida is defense and prey capture. When triggered by mechanical or chemical stimuli, the cnidocyte explosively discharges the cnida. The most common type of cnida is the nematocyst, which contains a coiled, barbed thread. Upon discharge, this thread rapidly everts and penetrates the target, injecting venom or anchoring the cnidarian to its prey or predator. Different species of cnidarians have evolved a variety of cnida types, each adapted for specific functions such as envenomation, entanglement, or adhesion. The complexity and diversity of cnida are key adaptations that have contributed to the ecological success of cnidarians.