They are Fasciola hepatica (common liver fluke or sheep liver fluke) ... These eggs develop in freshwater, using snails as an immediate host to undergo several developmental stages.

M. Adela Valero, Miroslava Panova, Ana M. Comes, Roger Fons, Santiago Mas-Coma, Patterns in Size and Shedding of Fasciola hepatica Eggs by Naturally and Experimentally Infected Murid Rodents, The ...