noun, plural: nectosomes
Siphonophores are marine invertebrates that are seen as colonies. A single specimen is actually a colony comprised of zooids. Each zooid in a colony is a single organism; however, it is interdependent to the other zooids comprising the colony and it would not be able to survive independently. The siphonophores may be classified into three groups based on the composition of their colony: (1) cystonects, (2) physonects, and (3) calycophorans. The cystonects form a colony comprised of pneumatophore and siphosome zooids. The physonects' colony is comprised of pneumatophore, siphosome, and nectosome zooids. The calycophoran colony lacks the pneumatophore and comprised of nectosome and siphosome zooids.1
The nectosome is the region in the colony that is comprised of the nectophores. Nectophores are the swimming bells of siphonophores. As the name implies, they are zooids specialized for swimming. They are the medusae that move the colony through the water. These nectophore zooids contract in a coordinated fashion, propelling the colony forward, backward, or in turns.1
In physonects, the nectophores or the nectosome region is found below the pneumatophore. In calycophorans, the nectosome is just above the siphosome.1
1Siphonophores. Siphonophores.org. Retrieved from [].