Larval Leaf Scorpionfish (photograph by Chris Newbert, Minden Pictures). Lacking any other defense, many larval fish have adapted transparency as a method of camouflage—such as this tiny, see-through larval leaf scorpionfish in Hawaii.
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.
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.