I recently traveled to Philippines to go scuba diving and concentrate on macro underwater photography. In other words I was going critter hunting, looking for animals so small that they could not be seen without a close up diopter.
I selected a wet lens made by that flipped in front of the port and added a close up diopter infant of a 105 mm lens. This tool is very hard to use as you have to get close to subject and marine tends to swim away when something is put millimeters away. However with patience it is possible to get some incredible results.
this is an egg cluster of some Clownfish I encountered in Anilao, Philippines.