Not sure what this guy is. Pic at night with flashlight. Not a mithrax, emerald or gorilla. Has a huge wingspan of almost 3 inches. Dark brown in color with large claws. Seems to be interested in algae but want to make sure. Thanks.
Keep an eye on the crab in question. If it truly is a porcelain, you should see it extend its feeding rakers from time to time to catch particles in the water column.