The utilization of cnidarian nematocysts by aeolid nudibranchs: nematocyst maintenance and release in Spurilla.

Some nudibranchs that feed on cnidarians are known to store nematocysts within cnidophage cells and use them for their own defense. Most of the nematocysts are in direct contact with the cytoplasm of the cnidophage. Nematocysts are not subjected to lysosomal enzymes because any phagocytic membrane that surrounded the nematocyst after engulfment does not persist. Cnidophage organelles are restricted to regions surrounding the nematocysts and may aid in the maintenance and development of the nematocysts. The release of cnidophages is initiated by a contraction of a dense muscle complex surrounding the cnidosac. Nematocysts do not discharge if the cnidophage membrane does not rupture upon release. A comparison of nematocysts maintenance in Spurilla neapolitana and nematocyst retention in other organisms is presented.