What does nematocyst mean?
A nematocyst is the specialized stinging structure inside a cnidocyte, a cell found in jellyfish, sea anemones, corals, hydras, and other cnidarians. Each nematocyst contains a tightly coiled, threadlike apparatus within a capsule. When triggered, the thread everts rapidly and may discharge with enough force to pierce prey, deliver substances, or deter predators. Collections of these structures can cover parts of an animal's tentacles and create what are commonly called stinging cells, although the precise biological terms distinguish the cell from the capsule within it. The term is chiefly used in zoology, marine biology, and discussions of venomous or stinging cnidarians. Understanding nematocysts explains how animals that appear soft and delicate can capture prey and defend themselves effectively.
nounA microscopic, capsule-like stinging structure found in cnidocytes, the specialized cells of jellyfish, sea anemones, corals, and related animals. It contains a coiled, threadlike structure that can discharge rapidly to capture prey or defend the animal.
- A specialized, capsule-like stinging organelle within a cnidocyte that functions in prey capture and defense.
"The jellyfish's nematocysts released stinging threads that adhered to the swimmer's skin."
"Cnidarian tentacles are densely equipped with nematocysts."
"Microscopic examination revealed that each discharged nematocyst had left its thread extending through the tissue."
The standard plural is nematocysts; the singular is nematocyst.
"The species uses thousands of nematocysts along its tentacles to capture prey."
A nematocyst essentially fires a microscopic harpoon: pressure inside the capsule triggers an everting thread that can pierce prey or a predator.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does nematocyst come from?
The word combines the Greek roots nēma, meaning “thread,” and kystis, meaning “bladder” or “sac,” referring to the capsule and its threadlike contents. It was coined in the early 19th century as a zoological term for the stinging capsule of cnidarians. The related term cnidocyte combines the same suffix meaning “cell” with cnid-, a root associated with stinging organisms.
Related word forms
How nematocyst is actually used
This is a technical zoological term. It is usually used in biological and medical contexts, especially discussions of cnidarians, jellyfish stings, and cnidocyte function. In modern biological usage, nematocyst specifically denotes the organelle, while cnidocyte denotes the cell containing it.
Easily confused with nematocyst
A nematocyst is the stinging capsule within a cnidocyte, whereas a cnidocyte is the entire specialized cell containing it.
A nematode is a roundworm, while a nematocyst is the thread-bearing stinging structure of cnidarians.