Seahorses have prehensile tails, which they use to cling to seagrass like little underwater monkeys. That's just one of the tricks that help make up for the fact that seahorses are some of the slowest swimmers in the animal kingdom. Their eating strategy is based on stealth, not speed.
Image: Longsnout Seahorse (Hippocampus reidi), a Creative Commons Attribution (2.0) image from nostri-imago's photostream