Pronunciation: [sˈiːnˈiːdə] (IPA) 
Cnida is a term used to describe specialized stinging cells found in cnidarians, such as jellyfish and coral. The spelling of this word may seem unusual, but it is derived from the Greek word 'knidē' meaning nettle or sea anemone. The 'c' in Cnida is pronounced as /k/ while the 'n' is pronounced as /n/ and the 'i' as /aɪ/ or long 'i'. The 'd' is silent, thus making the pronunciation of this word as /ˈnaɪdə/ or 'nye-dah'.
Cnida, also known as cnidocyte, is a specialized stinging cell found in cnidarians, which are a group of animals that includes jellyfish, sea anemones, and corals. The term cnida is derived from the Greek word knide, meaning "nettle" or "stinging nettle." Cnidae are unique to this phylum and are responsible for the characteristic stinging ability possessed by many cnidarians.
Cnidae are microscopic capsules that contain a complex, coiled tubule and are housed within special cells called cnidocytes. They are primarily used by cnidarians as a means of defense, prey capture, and immobilization. When triggered by physical contact, chemical signals, or changes in temperature, cnidocytes rapidly discharge their toxic contents. This discharge occurs through an extremely rapid process, which is usually accompanied by the extension of a barbed, harpoon-like structure called a nematocyst.
The contents of cnidocytes can vary among different species but often include venomous substances, such as neurotoxins, that are potent enough to paralyze or kill small prey organisms. The power and effect of these stinging cells can range from mild discomfort to extreme pain and may be potentially dangerous to humans.
In addition to their defensive and prey-capturing roles, cnidae are also essential for the movement of some cnidarians. By discharging these stinging cells in patterns, certain species can produce jets of water that function as a propulsion mechanism, allowing them to swim or crawl within their aquatic environments.
Overall, cnidae are an important adaptation found in cnidarians that contribute to their survival, feeding, and locomotion strategies.
The word "Cnida" comes from the Greek word "knidē" (κνίδη). In Greek, "knidē" means a nettle or a small stinging insect. The term was later adopted into scientific terminology to refer to specialized stinging cells found in certain organisms, particularly in the phylum Cnidaria, which includes jellyfish, sea anemones, and coral. These cells, called cnidocytes, contain nematocysts that can inject venom into prey or potential threats. Thus, the word "cnida" ultimately stems from the Greek word for nettle, reflecting the stinging and venomous nature of the organisms associated with it.
