[Class] Polycystinea Ehrenberg, 1838 - polycystines see Superclass Polycystinia Ehrenberg, 1838 Order Nassellaria Ehrenberg, 1875 see Class Nassellaria Ehrenberg, 1847 Family Plagiacanthidae Hertwig, 1879 Genus †Peridium Haeckel, 1881 1 †Peridium longispinum Jørgensen, 1900 2 †Peridium spinipes Haeckel, 1887