invasive species gastropods physa acuta in a lake on a leaf of the invader pistia

pistia southern ukraine gastropods invasive invader alga algae aquatic plant plants araceae common duckweeds duckweed floating flora green background growth species lake leaf leaves lemna turionifera lemnaceae natural nature nile cabbage physa acuta stratiotes pistieae pond pool rootless seaweed shellflower spotless watermeal surface swamp tiny water lettuce wolffia animal