The flower is as open as it is going to get. The white parts are the three stigmas, the female parts that receive the pollen. This flower has rudimentary petals and green sepals. This is a very nice closeup of the Vallisneria
flower by asukawashere.
What you are calling the pod is the three fused ovaries of the flower. If fertilized, this part will enlarge and become a fruit with a large number of seeds inside.
The Blyxa flower, in contrast has three prominent petals and a rather small ovary. The stem of the flower is not spiraled. The flower pokes straight up out of the water. It has both sexes: carpels (female) and stamens (male). Vallisneria
has male plants that produce male flowers and female plants that produce female flowers.