Are these deep-sea predators a single animal or a complex, living colony?

Nature · Published 3 October 2026 Swipe more like this →

In short: Siphonophores blur the line between individual and colony. These gelatinous predators are actually aggregates of specialized, genetically identical units called zooids. Each zooid performs a specific role—from propulsion and digestion to reproduction—creating a functional, rope-like organism that can grow longer than a blue whale in the deep ocean.

Siphonophores are cnidarians belonging to the order Siphonophorae, a group that challenges our standard definition of an individual. Unlike typical animals, a siphonophore begins as a single fertilized egg that undergoes budding to produce a colony of zooids. These zooids are multicellular units that, while genetically identical, differentiate into specialized roles. Some, known as gastrozooids, are dedicated to feeding, while others, like nectophores, provide jet propulsion for the colony. Because these units are physically and functionally integrated, the entire structure acts as a single, coordinated organism.

The diversity of these colonies is vast, with approximately 175 to 194 species currently described. They are categorized into three primary body plans: Cystonectae, Physonectae, and Calycophorae. These classifications are largely based on the presence of gas-filled floats called pneumatophores or swimming bells called nectophores. Some species, such as the giant Apolemia discovered in 2020, can reach massive proportions, with one specimen measured at 47 meters in length. Their survival in the deep sea is aided by remarkable adaptations, including bioluminescence used for defense or as a lure to attract prey, and a modular design that allows the colony to survive even if individual parts are damaged.

Studying these creatures is notoriously difficult due to their extreme fragility and deep-sea habitats. Most specimens are destroyed during collection, forcing researchers to rely on in situ observations from submersibles and molecular phylogenetics. Recent genomic analyses have helped clarify their evolutionary history, suggesting they evolved from simpler colonial hydrozoans. As we continue to explore the ocean, siphonophores remain a primary subject for understanding how complex, multi-part organisms can emerge from simple, clonal beginnings to dominate the pelagic zone.

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