Cnidocyte
A cnidocyte (also known as a cnidoblast) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida (pl.
This discharge takes a few microseconds, and is able to reach accelerations of about 40,000 g.[1][2] Research from 2006 suggests the process occurs in as little as 700 nanoseconds, thus reaching an acceleration of up to 5,410,000 g.[3] After penetration, the toxic content of the nematocyst is injected into the target organism, allowing the sessile cnidarian to capture the immobilized prey.
Recently, in two sea anemone species (Nematostella vectensis and Anthopleura elegantissima), the type I neurotoxin protein Nv1 was shown to be localized in ectodermal gland cells in the tentacles, next to but not in nematocysts.
[5] Trimers of mini collagen proteins assemble through their terminal cysteine-rich domain, forming highly organized and rigid supra-structures.
Observational studies typically used a tentacle solution assay with a chemical stimulant to create discharge and cameras to record them.
[10] This is possibly the case for other jelly species and hence one cannot generally infer nematocyst static traits to prey size.
By contrast, the two penetrant types of cnidocytes present in this species display a much broader localization, on the outer epithelial layer of the tentacles and body column, as well as on the pharynx epithelium and within mesenteries.
[13] In the sea anemone Nematostella vectensis, some minicollagens display a differential expression pattern in different cnidocytes subtypes.
Developing nematocysts first undergo multiple rounds of mitosis without cytokinesis, giving rise to nematoblast nests with 8, 16, 32 or 64 cells.
[15] In the Anthozoan sea anemone Nematostella vectensis, nematocytes are thought to develop throughout the animal from epithelial progenitors.
Then, an early maturation phase enables the formation of long arrays of barbed spines onto the invaginated tubule through the condensation of spinalin proteins.
Other cnidarians, such as the jellyfish Cyanea capillata (the "Lion's Mane" made famous by Sherlock Holmes) or the siphonophore Physalia physalis (Portuguese man o' war, "Bluebottle") can cause extremely painful and sometimes fatal stings.
On the other hand, aggregating sea anemones may have the lowest sting intensity, perhaps due to the inability of the nematocysts to penetrate the skin, creating a feeling similar to touching sticky candies.
Besides feeding and defense, sea anemone and coral colonies use cnidocytes to sting one another in order to defend or win space.
Animals in the phylum Ctenophora ("sea-gooseberries" or "comb jellies") are transparent and jelly-like but have no nematocysts, and are harmless to humans.
Certain types of sea slugs, such as the nudibranch aeolids, are known to undergo kleptocnidy (in addition to kleptoplasty), whereby the organisms store nematocysts of digested prey at the tips of their cerata.
