Abundance,feeding behaviour and nematocysts of scyphopolyps (Cnidaria) and nematocysts in their predator,the nudibranch Coryphella verrucosa (Mollusca)

The abundance of Aurelia and Cyanea scyphopolyps on Laminaria saccharinawas higher in sheltered, shallow areas compared with more exposed or deepones. Liberated planulae probably were not transported far away fromstranded and trapped jellyfish and settled nearby, preferably in patches onthe downward side of the Laminaria thallus. The principal prey for thescyphopolyps seems to be small copepods and the cladocerans Podon sp. andEvadne sp., which are abundant in surface waters during the summer.Temporarily abundant planktonic organisms, e.g., Sagitta setosa,Pleurobrachia pileus and hydromedusae might, also be important prey.Harpacticids, halacarideans and Corophium sp., whose natural habitat is onL. saccharina, were not captured by the scyphopolyps. Scyphopolyps culturedin running sea water rich in detritus and phytoplankton fill their enteronwith organic substrates, particularly diatoms. A new category ofheterotrichous microbasic rhopaloid nematocysts was identified in thescyphopolyps. These rhopaloids were earlier included within the eurytelesand were not considered to be separate nematocysts. They are distinctivefrom the euryteles due to the two swellings on their discharged shaft. Theabsence or presence of the nudibranch Coryphella verrucosa on laminarianthalli possibly has an effect on the number of scyphopolyps, as thisnudibranch consumes numerous scyphopolyps. Isorhizas and the new category ofrhopaloid nematocysts, identical to those present in the Aurelia polyps,occurred in the cnidosacs of examined C. verrucosa. The proportion ofrhopaloid nematocysts compared with a-isorhizas was noticeably higher in C.verrucosa than in scyphopolyps. The nudibranch may selectively storerhopaloids.