Morphology and development of the Portuguese man of war, Physalia physalis

Abstract

The Portuguese man of war, Physalia physalis, is a siphonophore that uses a gas-filled float as a sail to catch the wind. It is one of the most conspicuous, but poorly understood members of the pleuston, a community of organisms that occupy a habitat at the sea-air interface. The development, morphology, and colony organization of P. physalis is very different from all other siphonophores. Here, we propose a framework for homologizing the axes with other siphonophores, and also suggest that the tentacle bearing zooids should be called tentacular palpons. We also look at live and fixed larval and non-reproductively mature juvenile specimens, and use optical projection tomography to build on existing knowledge about the morphology and development of this species. Previous descriptions of P. physalis larvae, especially descriptions of budding order, were often framed with the mature colony in mind. However, we use the simpler organization of larvae and the juvenile specimens to inform our understanding of the morphology, budding order, and colony organization in the mature specimen. Finally, we review what is known about the ecology and lifecyle of P. physalis.