[2] Despite appearing to be a single multicellular organism, they are actually a floating colony of polyps and medusoids, collectively known as zooids.

The genus Apolemia, named by Baltic-German physician and naturalist Johann Friedrich von Eschscholtz, was first documented in 1815 with the discovery and description of Apolemia uvaria (the "string jellyfish"), by French naturalist Charles Alexandre Lesueur off the coast of Europe.

Apolemia are carnivorous invertebrates, which have been documented to feed on small fish, crustaceans, copepods, other plankton, and even other siphonophores.

The orientation of these zooids differs to achieve optimal function within the colony, serving a role in locomotion, propulsion, feeding, and defense.

Most Physonectae are described as jellyfish-shaped, though Apolemia proves to be an exception in this instance, aligned more laterally than rounded, such as conventional jellyfish.

Predatory siphonophores such as Apolemia rely on nematocyst rows to inject toxins and incapacitate prey for the colony to feed.