Slender Filefish 

Monacanthus tuckeri

The Slender Filefish likes hiding in and around sea plumes and sea rods. You will occasionally find them trying to blend in with the branches. They are only  2-3 inches long, which makes them even harder to spot. They can change colors rapidly from the very lime green as in the lower pictures, to almost a chocolate brown. (the bottom 9 set of pictures is the same fish). Generally not found in real shallow water, but in the 3-8 foot depths as these were (they can be found in depths of 60 feet, but I'm speaking of snorkel depths). Like their cousins, the Orangespotted Filefish, they have a front dorsal spine that they will raise and lower and also a dewlap (extendable belly flap) that they extend and retract.