I remember being confused about the taxonomic placement of sea horses. For a while, I wasn't sure if they were even vertabrates before I finally learned that sea horses, along with pipefishes and sea dragons, were in fact fishes in the family Syngnathidae.
This weekend we are in Atlanta, Georgia and yesterday spent several hours at Georgia Aquarium. The tank of sea dragons provided a brief glimpse into the intriguing behavior of these intriguing creatures.
While watching this particular species, whose name I neglected to note, I noticed that its sole method of propulsion seemed to have been by the use of the feathery fin around its neck (arrow in the photo).
Despite the rather feeble appearance of the fin, however, the sea dragon was able to maneuver itself gracefully. To escape from their predators, I don't think the sea dragons use speed, which they probably don't have, but must instead rely on camouflage supplied by their peculiar body shapes and the numerous appendages. During the sea dragons' evolution presumably from ancestors that were more fish-like in appearance, only the pectoral fins seem to have survived in a modified form to supply the necessary maneuvering ability among the protective cover of sea weeds and the like.
These are all speculations, of course, that I jotted out during a moment of creativity. Correct me if I am wrong.