This plant-like organism is really an animal, although it does have plants (algae) living inside of it. The green color of this animal comes from a symbiotic algae, called zooxanthellae, living inside its gut.
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.
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.