Martin, R. and P. Walther. 2003. Protective mechanisms against the action of nematocysts in the epidermis of Cratena peregrine and Flabellina affinis (Gastropoda, Nudibranchia). Zoomorphology 122:25-35.
Aeolid nudibranchs not only eat cnidarians, but they also live among their nematocyst-armed tentacles. Flabellina have a highly differentiated skin that contains specialized vesicles in order to be able to live within the tentacles. How do epidermal vesicles work to protect Flabellina affinis' skin when being under constant attack?
The epithelium of the skin and the gut are lined with a monolayer of epidermal vesicles, mucus glands, and cilia. These vesicles contain filamentous spindles, which are excreted when attacked by nematocysts. When a nematocyst fires, the skin of F. affinis appears unharmed, the impact being somehow absorbed or interrupted.
F. affinis and C. peregrine "were brought into contact with hydroud cnidophores or tentacles" and then placed in fixatives. The resulting microscopy photos showed that the surface of the epidermis on the skin and in the gut was a complex of discharged nematocysts, mucus and free spindles. Cnidophore nematocysts entered the epidermis and began cell lysis, but the slug was able to shake off the nematocysts after 10-25 minutes.
Martin and Walter found that through a merocrine secretion, spindles are excreted at different concentrations depending on the severity of nematocyst attack. Spindles are also excreted in the lumen of th gut to protect the gut while eating. The contents of the vesicles are excreted upon impact with nematocysts, and the spindles tangle with the nematocyst threads.
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