Chondrophore

The chondrophores or porpitids are a small and unusual group of hydrozoans. They are the family Porpitidae.Schuchert, Peter 2012. The hydrozoa directory. Muséum Geneve

They all live at the surface of the open ocean, and are  colonies of carnivorous, free-floating hydroids. Their life-style in the plankton is similar to that of pelagic jellyfish.

The chondrophores look like a single organism but are  cooperatives of polyps.

The most familiar members of the family Porpitidae are the blue button (Porpita porpita) and the by-the-wind sailor (Velella velella).

 Structure 
Chondrophores may look like a jellyfish, but they really are not. Like the siphonophores they are not a single animal. They are a colony of clones, genetically identical zooids. These zooids are small, highly modified individual polyps. Though structurally similar to other cnidarians, the zooids do not live by themselves: they are attached to each other. Each type of zooid depends for survival on the others doing what it cannot do by itself.

This kind of set-up is also found in the siphonophores: the Portuguese man o' war. They evolved independently, and are classified in different orders.

 Fossil record 
A rare soft-bodied fossil was got from  Mississippian strata in northeastern Kentucky. It was interpreted as a chondrophorine float.Yochelson, Ellis L.  and Mason, Charles E. 1986. A chondrophorine coelenterate from the Borden Formation (Lower Mississippian) of Kentucky, Journal of Paleontology. 60, 5, 1025-1028.  The origin of the group was probably in the Neoproterozoic era, some 650540 million years ago.

 References 

Category:Cnidarians