Once the prey is fast and has ceased to struggle, it is brought to the mouth, which opens wide to receive it, by the contraction and the contortions of the tentacles, the column, and the peristome.
"Freshwater Sponges, Hydroids & Polyzoa"
Nelson Annandale
During each forward movement the column is arched downwards so that the peristome is in contact with the surface along which the animal is moving.
"Freshwater Sponges, Hydroids & Polyzoa"
Nelson Annandale