1. It is shown, by laboratory observations, that the marine hoplonemerteans Tetrastemma elegans (Girard, 1852), Zygonemertes virescens (Verrill, 1879), and Amphiporus ochraceus (Verrill, 1873), feed in a suctorial manner on small crustaceans.
2. Amphipods are the preferred crustacean prey, with an overwhelming preference being shown for Corophium acherusicum Costa, over several other species tested. Tetrastemma kills this amphipod at a greater rate than does Zygonemertes.
3. The prey is killed with a violent thrust of the proboscis, which in some manner punctures the exoskeleton and injects a toxin. The head is inserted into an opening produced on the ventral side, and the stomach is everted. A peristaltic action of the whole body is associated with a suction that removes nearly all of the internal contents of the prey.
4. The feeding behavior of the suctorial monostyliferans is compared with the macrophagous species. In at least one family, the Tetrastemmatidae, both feeding mechanisms are represented.
5. Laboratory studies on the food and food preferences of the suctorial species are essential in determining their particular ecological niches.
