Stichocysts

Stichocysts are specialized extrusomes found in dinoflagellates, a group of single-celled protists. These organelles are typically rod-shaped and contain coiled threads that can be rapidly discharged from the cell. The primary function of stichocysts is defense against predation. When a dinoflagellate encounters a predator, it can expel its stichocysts, which unfurl into long, sticky filaments. These filaments can entangle and deter the predator, giving the dinoflagellate a chance to escape.

The structure of stichocysts is complex. They are membrane-bound organelles containing densely packed material. Upon stimulation, a pore in the dinoflagellate's pellicle opens, and the stichocyst is everted. The rapid extrusion is thought to be driven by osmotic pressure or a mechanical force. The discharged filaments can vary in length and thickness depending on the species of dinoflagellate.

In addition to defense, stichocysts may play a role in other cellular processes, although this is less understood. Some studies suggest they could be involved in anchoring or even in the capture of prey in certain species. The presence and morphology of stichocysts can be important taxonomic characteristics for identifying different dinoflagellate species. They are a fascinating example of sophisticated cellular defense mechanisms in the microscopic world.