Aquatic antagonists: indirect nematocyst envenomation and acute allergic contact dermatitis due to nudibranchs.

It is well-known to swimmers, divers, and beachgoers that coelenterates such as the Portuguese man-of-war (Physalia physalis), true jellyfish such as the box jellyfish, sea anemone, true coral, and fire coral can inflict painful and sometimes fatal stings. As a result, these organisms are avoided by humans and most sea creatures; however, indirect contact with the skin may occur. For example, coelenterates may release toxic substances into the marine environment, leading to sensitization in swimmers even without contact with stinging tentacles.1 Subsequent contact with the same or crossreacting substance may lead to a severe episode of acute allergic contact dermatitis. The Portuguese man-of-war, true jellyfish, sea anemone, true coral, and fire coral (a hydroid) all contain nematocysts within their tentacles. Portuguese men-of-war may have tentacles up to 27-m long with as many as 1 million nematocysts.2 During severe storms, tentacles may break away from the primary organism and envenomate unsuspecting individuals. These reactions may be just as severe as attacks with live jellyfish, especially in sensitized individuals. Interestingly, the stinging nematocysts of coelenterates are not feared by all. In fact, there are several organisms that utilize these stinging cells for defense. In particular, Tremoctopus violaceus,3 a member of the blanket octopuses, tears off tentacles of P physalis for offensive and defensive purposes. Nudibranchs, also called sea slugs, take advantage of stinging nematocysts in a different and fascinating way. They actually incorporate the nematocysts as outgrowths on the body after eating portions of the Portuguese man-of-war tentacles. This review focuses on this nudibranch method of defense and how it pertains to human envenomation.