Stinging mechanism used for defence and prey capture by Hydra and other members of the Cnidaria (Coelenterata). It is located within a specialised cell, the nematocyte and consists of a capsule containing a coiled tube. When the nematocyte is triggered, the wall of the capsule changes its water permeability and the inrush of water causes the tube to evert explosively ejecting the nematocyst from the cell. The tube is commonly armed with barbs and may also contain toxin.
This entry appears with permission from the Dictionary of Cell and Molecular Biology
(11 Mar 2008)
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