siphonophores

Siphonophores are an order of hydrozoan cnidarians within the class Hydrozoa. They are colonial animals rather than a single individual, consisting of many specialized zooids that are genetically identical and physically integrated to function as a single organism. Siphonophores develop from a single fertilized egg, budding repeatedly to form an elongated colony with distinct, interdependent parts.

Colonies are organized into two main regions: the nectosome, which bears swimming zooids called nectophores that provide propulsion, and the siphosome, which carries feeding, defensive, sensory, and reproductive zooids. Feeding zooids (gastrozooids) capture prey with nematocysts, while dactylozooids defend the colony. Palpons assist digestion and may carry nematocysts, and gonophores give rise to offspring. Many species also possess a pneumatophore, a gas-filled float that enables surface drifting.

Ecology and distribution: Siphonophores are predominantly pelagic and occur in oceans worldwide, from the surface to great depths. They are efficient predators of small plankton such as copepods and sometimes small fish larvae. Some species have extremely long tentacles that extend far beyond the main body, contributing to their overall size. The Portuguese man o’ war (Physalia physalis) is a well-known siphonophore, notable for its float and venomous tentacles.

Interactions with humans: Stings from siphonophores can irritate the skin or cause more serious reactions, depending on species and exposure. They are typically not aggressive toward humans but can be hazardous if touched. Siphonophores are of interest to scientists for their complex colonial organization, biomechanics of movement, and bioluminescence in many species.