A bait ball, or baitball, occurs when small fish swarm in a tightly packed spherical formation about a common centre. It is a last-ditch defensive measure adopted by small schooling fish when they are threatened by predators.
This animal, the Leafy Seadragon, is a Threatened species. They are threatened by collecting for use in Chinese medicine (and by habitat loss). Just one more example of the beautiful natural world exploited by idiotic traditional Chinese cruelty.
Jelly fish are strange, with of their body water, they don't have a brain. All jelly fish have a squishy hemisphere for a head and deadly stingers that are directly below the head. The stingers kill fish, and some jelly fish can kill or wound a human.
Yes, this is an animal. The Spanish dancer (Hexabranchus sanguineus - meaning "blood-colored six-gills") is a dorid nudibranch (sea slug). I think it's great color and design inspiration for a crocheted afghan.