Parazit hayot tarziga o'tish jarayonida o'zining asl epidermisini yo'qotgan, uning o'rnida neodermis-tegument hosil bo'lgan barcha yassi parazit chuvalchanglarni o'z ichiga olgan guruh. Tana qoplag‘ichi tegument deb ataladigan kipriksiz epiteliydan iborat.