The chorionic surface ofBelostoma lutariumcan be divided into three distinct morphological regions. The basal area contains the hydropyle which has a filamentous central core and long excrescences surrounding the core. The medial area is composed of polygons that have indistinct ridges which makes demarcation not as well defined as on the apical cap area. Each medial polygon has twelve to twenty‐one areopyles. The apical cap area has polygons with distinct ridges and is covered with a plastron network. There are six to eight micropyles in a semi‐circle on a raised portion of the apical end. The aeropyles in this region are situated at the junction of several polygons and they contain an inner meshwork. The internal structure of the chorion consists of porous layers and spaces.