I could not find the original source. The website cited as source in most places (http://www.handlerphoto.com/) is redirected to a new site (http://www.aquaterrafilms.com/). Here it is Mauricio Handler’s Instagram, I was not able to search because it forces you to log in.

Article with more info: Diver photographs ‘Cookie Monster of the Sea’ - Men’s Journal:

(…) the reefs of Curacao in the Caribbean.

(…) a purple sea sponge that strongly resembled the famous Cookie Monster Muppet of “Sesame Street” fame.

(…) the Cookie Monster was actually three tube sponges that had fused together over time. (Sea sponges, while they may appear to be plant-like, are actually multi-cellular animals that attach to the sea floor, or to reefs, and feed by filtering particles from currents.)

HD version from Animal Eel HD Wallpaper