The spectacular diversity of siphonophores

July 12, 2013

A group of collaborators from Brown University are on board this expedition. Casey Dunn’s lab investigates how evolution produced the diversity of life. On this expedition, they are focused on siphonophores, which are colonial cnidarians. Most of the siphonophore species are found in the deep-sea and they are poorly known due to the difficulty in sampling these delicate animals from the deep sea. Casey’s group is most interested in the evolution of their colonial-level organization and development, but because so many siphonophores are still as yet unknown to science, the group also works with the Haddock lab on systematics, morphology, and natural history.

The morphological diversity of siphonophores found in the deep sea is spectacular. They range from the longest animal in the world (Praya), to rocket-shaped (Kephyes), long and frilly (Bargmannia), and small and round, among many other forms.

A diverse collection of siphonophores. Clockwise from upper left: Praya dubia, Kephyes ovata, a benthic siphonophore, and Bargmannia elongata.

A diverse collection of siphonophores. Clockwise from upper left: Praya dubia, Kephyes ovata, a benthic siphonophore, and Bargmannia elongata.

Casey’s group is collecting a variety of siphonophores on this cruise. They will isolate the RNA and sequence thousands of genes to develop a phylogeny (the evolutionary development and history of a species and higher taxonomic grouping of organisms). They are also interested in the genes expressed by the different bodies within a siphonophore colony. For example, there are feeding, reproductive, and swimming parts that make up each colony.

Stefan Siebert is working on the species description of this siphonophore in the genus Apolemia. At the top is the nectosome (head), which includes the swimming bells. At the bottom, the shaggy part, is the tail, made up of feeding, reproductive, and protective bodies. Photo by Stefan Siebert.

Stefan Siebert is working on the species description of this siphonophore in the genus Apolemia. At the top is the nectosome (head), which includes the swimming bells. At the bottom, the shaggy part, is the tail, made up of feeding, reproductive, and protective bodies. Photo by Stefan Siebert.

Steve Haddock, Casey Dunn, Stefan, and another collaborator, Phil Pugh (National Oceanographic Centre in the United Kingdom) have a publication recently accepted describing two of the most common species of Apolemia that we see here in the Monterey Bay region.

Studying the genes expressed in each body of the colony will give clues to the functional evolution within the siphonophores but also has implications for the understanding of functional specialization on a cellular level in all organisms and therefore, evolution throughout the tree of life.

Steve and Casey work together to carefully remove a delicate siphonophore from a detritus sampler.

Steve and Casey work together to carefully remove a delicate siphonophore from a detritus sampler.


Freya sorts the different bodies of the colony from a collected siphonophore.

Freya sorts the different bodies of the colony from a collected siphonophore.


Stefan explains the morphology of this undescribed siphonophore. He spent a lot of time in the lab taking detailed photo-montages of the specimens he works on to better understand each part, as well to use in figures for publication.

Stefan explains the morphology of this undescribed siphonophore. He spent a lot of time in the lab taking detailed photo-montages of the specimens he works on to better understand each part, as well to use in figures for publication.

—Susan von Thun