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There were two schools‐of‐thought regarding the evolution of the siphonophores themselves. One supported the idea that siphonophores were highly modified medusoid organisms, giving rise by budding from the sub‐umbrella to secondary medusae and polyps (Haeckel 1866; Hatschek 1888). The other school‐of‐thought regarded siphonophores as floating colonies of hydroid polyps, showing division and specialization of labor, and budding off medusae (Leuckart 1848; Vogt 1854; Agassiz 1883).

Chondrophora were recognized as a special case by LeLoup (1929) and Garstang (1946), who believed them to be polypoid organisms showing affinities to Tubularia‐type hydroids, as they are classified today. Thus, the new scheme, which may seem to be off‐base from the morphological perspective, not only has more substance than was initially obvious but has a long history of argument behind it.

Like other Anthomedusae, Tubularia is an athecate hydroid. It does not release free medusae and its hydranth bears numerous gonophores whose eggs develop first into planulae then into actinulae before release (Figure 3.39). In contrast, both Vellela and Porpita have a free medusa stage, and these are presumably dioecious. Either the fertilized egg develops into planula‐conaria larva, or planula larvae are released from medusae to become conaria.