The region of a siphonophore colony that bears nectophores (medusae specialized for propulsion).

A nectosome is an order of Hydrozoa (various simple and compound polyps and jellyfish) consisting of various free-swimming or floating pelagic, mostly delicate and transparent, and often colored forms that are usually regarded as compound animals composed of zooids modified to perform various functions for the colony. Examples are feeding, defense, and locomotion which sometimes have two or more zooids in the form of a bell so that, by their contractions, they cause the colony to swim, and which often have a hollow float which keeps the colony afloat.