Body form influences energy expenditure by swimming hydromedusae. The fineness ratio (the ratio of maximum body length to body width) is an index of this expenditure and may be related to medusan foraging strategy. A general scheme is proposed in which foraging modes are classified into ambush and cruising types. Ambush predators are characterized by streamlined bells with fineness ratios greater than 0.5. Cruising medusan predators are characterized by fineness ratios below 0.5. While energetically expensive for swimming, oblate body forms of cruising medusae enhance water movement past tentacles and capture surfaces and therefore contribute to prey capture. The two foraging strategies are predicted to result in: first, different patterns of swimming activity in the presence of prey and second, different physiological responses to periods of starvation.