Stinging cells

A well-fed hydra (Fig. 1-13) appears immortal. Its body cells are sloughed off and replaced at a steady rate so that within a month or so its body has been completely renewed 35 The hydra contains only ten cell types. These include two kinds of stem cells that give rise to the ectodermal and endodermal cells of the body wall as well as small interstitial stem cells (Fig. 1-13) that differentiate nerve cells, germ cells, and the nematocytes or stinging cells. Of the 105 cells in a hydra about 3600 are interstitial stem cells. Each day they generate 400 nerve cells and 1800 nematocyte precursor cells as well as 3500 new interstitial cells. 

Cnidaria Jellyfish, corals, sea Two body layers, stinging cells,... 

Shallow-water inhabitants are subject to a variety of predators but protect themselves with an arsenal of defense mechanisms. Sea urchins are covered in sharp spines, and anemones are armed with stinging cells. Sponges wage chemical warfare on their foes by producing toxins, and mobile animals simply... 

Each tentacle will be covered with millions of these stinging cells, resulting in a large amount of venom being injected over a wide area... 

The Bluebottle is eaten by other animals, including the loggerhead turtle. The small Bluebottle Fish lives among the tentacles of the Bluebottle and feeds on the tentacles, which are constantly regenerated. Clown Anemone Fish and Yellow-Jack Fish reportedly have a similar relationship and all are nearly immune to the poison from the stinging cells. 

Symbiosis (or mutualism) is a relationship between dissimilar organisms in which both partners benefit (Hale et al, 1995). An example is the symbiosis between the hermit crab Pagarus and the sea anemone Adamsia palliata. The anemone attaches to the crab s shell and obtains food scraps from the crab. The crab is camouflaged by the anemone and defended by its stinging cells. 

You may have heard of this before, but it seems that it may just be an old wives tale. Washing the area of the sting with saltwater is recommended so as to deactivate any of the stinging cells from the jellyfish that may be present on your own skin. Fresh water may actually reactivate the cells that caused the sting, causing you further pain. 

The term Cnidaria derives from the Greek word fenide, nettle. The presence of stinging cells led to the division of the former phylum of Coelenterata into the Cnidaria, which are equipped with cnidocytes, and the Ctenaria (Ctenophores), which are not. 

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