Why is the Portuguese man-of-war considered a colonial hydrozoan?

The Portuguese man-of-war (Physalia physalis) is classified as a colonial hydrozoan because it is not a single individual, but rather a complex colony composed of numerous specialized, interdependent organisms called zooids.12

Unlike many other cnidarians, such as jellyfish, which are individual organisms, the Portuguese man-of-war functions through a division of labor among four distinct types of polyps, each performing a specific biological role necessary for the survival of the entire colony:2

• Pneumatophore: An uppermost, gas-filled bladder that acts as a float and sail, allowing the colony to drift on the ocean surface.2
• Dactylozooids: Tentacles equipped with nematocysts used for defense and capturing prey.2
• Gastrozooids: Digestive polyps that attach to and consume prey.2
• Gonozooids: Reproductive polyps responsible for the colony's propagation.2

Because these specialized units are physically integrated and rely on one another to feed, move, and reproduce, the Portuguese man-of-war is defined as a colonial hydrozoan within the order Siphonophora.234