In order to study the early development of Planocera reticulata ,embryos without egg-shell and larva were obtained using in vitro fertilization, and examined by scanning electron microscopy (SEM). Typical spiral cleavage was observed since the third cleavage. Several micromeres at proximal end of animal pole tended to form an invagination during blastula and gastrula stages. Planktonic larva swam freely with the cilia, which were emanated from the epidermal plates. At the ventral surface of larva, a rank of long cells was situated on the ventral part of embryo along median line. Demersal larva sank to the bottom and opened the external mouth, while at that time the number of cilia decreased obviously. Our results allow a comparison between P.reticulate and other polyclad flatworms in cleavage pattern and larval development. The unexpected finding of a special apical invagination of the blastula and gastrula stage embryos in polyclad P.reticulata was discussed.