The use of cnidarian nematocysts by the aeolidian nudibranch Cratena pilata
Nudibranchs feed on anemones and hydroid polyps. The ingested cnidarian nematocysts are stored in cerata, dorsal extensions of the gut, and used to defend against predatation. Specialized smooth muscle sacs in the cerata, the cnidosacs, contain modified epithelial cells, the cnidophages, that hold the nematocysts. Light microscopic and behavioral studies indicate that, upon adequate stimulation, the cnidosac and cerata contract, opening the ceras tip and releasing the stored nematocysts. Ultra-thin sections revealed that the smooth muscle cells of the ceras encompass a network of caveolae and that synaptic terminals containing dense-cored and clear vesicles impinge on the muscles of the cnidosac. Penetrant nematocysts from Ectopleura crocea, and spirocysts from Metridium senile were found within the cnidophages.^ Anti-α-tubulin immunoreactivity revealed nerve fibers running along the length of ceras muscle and throughout the cnidosac muscle. Nerves associated with the muscles of the ceras and cnidosac labeled with anti-serotonin antibody. Abundant FMRFamide immunoreactivity occurred within the somata of the nerves innervating the muscle of the ceras and cnidosac. No dopamine immunoreactivity was found.^ The head, rhinophores, ablated cerata, and tail of specimens of C. pilata responded to applications of force in a dose-dependent manner. The force required to eject nematocysts from half the animals (EC 50) was significantly lower for the rhinophores than for the head, and significantly lower for the left rhinophore than for the right.^ The rhinophores, head, individual cerata and tail responded to acidic solutions in a dose-dependent manner. Solutions above pH 3.5 evoked no responses. The EC50 concentrations for the rhinophores were significantly higher (i.e. less acidic) than those for the head and/or cerata. These observations suggest that a predator, such as a fish, would be stung by ejected nematocysts, if the head or rhinophores of a nudibranch were bitten with sufficient force, and that, if the nudibranch were swallowed into the stomach (pH of 2.0), the fish would continue to be stung, or poisoned, thus discouraging it from eating another nudibranch.^
Biology, Neuroscience|Biology, Physiology
"The use of cnidarian nematocysts by the aeolidian nudibranch Cratena pilata"
Dissertations and Master's Theses (Campus Access).