Penniform cone descending

Each aquarium tank had a glass lid, which was kept wet by the spray from aeration. Occasionally a mollusk would climb the tank wall, out of the water, and cross (upside down) along the glass lid. When this small penniform cone had gone about halfway across the lid, it decided to descend again. It did this by using its mucus trail as a spider would use a silk strand. In this photograph, the cone was suspended in mid-water on its mucus trail, which in turn was attached to the tank lid. Over the first few centimeters of its descent, the cone was dangling in the air between the lid and the water surface. In addition to an interesting application of a mucus trail, this demonstrates the trail's toughness. Back in Berkeley, we kept three mature cat cones in a covered twenty-gallon tank. I observed one of them performing the same maneuver.