Glaucus atlanticus

Glaucus atlanticus is a small pelagic sea slug that floats upside down at the ocean surface and feeds on venomous siphonophores. It can sequester their stinging cells for its own defense.

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Surface tension: The tendency of a liquid surface to resist deformation because of cohesive molecular forces. Glaucus hangs beneath the surface film, which helps support its inverted floating posture.
Nudibranch: A diverse group of marine gastropod mollusks, usually lacking an external shell as adults. Glaucus is a nudibranch with a highly specialized pelagic lifestyle.
Portuguese man o’ war: A colonial siphonophore with long venomous tentacles and a gas-filled float. It is a well-known prey item whose stinging cells Glaucus can appropriate.
Glaucus marginatus: A small pelagic sea slug closely related to Glaucus atlanticus and found in warm ocean waters. It is a similar surface-dwelling Glaucus species, distinguished from the Atlantic species by taxonomy and range.
Pneumatophore: A gas-filled float found in certain siphonophores, including the Portuguese man o’ war. This sail-like float keeps one of Glaucus’s principal prey at the surface.
Gastropoda: A large class of mollusks that includes snails, slugs, limpets, and their relatives. Glaucus belongs to this mollusk class despite its drifting, slug-like form.
By-the-wind sailor: A colonial hydrozoan that floats at the ocean surface on a small sail-like structure. It shares the surface-drifting habitat and can also be consumed by Glaucus.
Glaucus bennettae: A species of pelagic sea slug in the genus Glaucus, described from the Indo-Pacific region. Its recognition as a separate species illustrates diversity within the genus.
Kleptocnidy: The sequestration and reuse of stinging cells taken from another organism. Glaucus stores prey-derived nematocysts in specialized tissues and uses them defensively.
Cerata: Finger-like projections on the backs of many nudibranchs that can aid respiration, defense, or digestion. Glaucus’s branching cerata contain tissues where stolen stinging cells are concentrated.