Siphonophores are members of the order Hydrozoa, and include species such as the Portuguese Man ‘o War. Though they appear to be similar to jellyfish in form, they’re actually composed of many smaller organisms, grouped together in specialized colonies.
You can see the full colony of Physophora hydrostatica in the center of this illustration. At the top left and top right, the specialized gas bladders are isolated and viewed from above. On the bottom left and right, the “body” (center trunk) of the colony is shown without any polyps attached, viewed from top and from bottom.
Kunstformen der Natur [Plate 37]. Ernst Haeckel, 1904.