This view on the under side reveals the reason why I thought this beetle to be the species hyalinus (glass like): you can see the eggs through the abdomen. It seems minutus is very transparent also. When resting Laccophilus holds its hind legs completely under the body, because the thigh (femur) is hold in a straight forward position. It looks like this happens after each swimming stroke, making the forward movement a bit jerky, with a short sliding through after each stroke. The beetle is able to make remarkable high jumps with its hind legs when out of the water, this one suddenly jumped of the table, fortunately I could retrieve it.

The "slime", visible at the low border of the picture, is silicon kit on the glass.