Nemopilema nomurai polyps can capture only small ang slow-swimming prey such as ciliates, their own planulae, rotifers, copepods, planktonic larvae, and Artemia nauplii in the laboratory. It is worth nooting that N. nomurai planulae were suitable food for young polyps with 4-8 tèntaclès and also that excess feeding of Artemia nauplii resulted in high polyp mortality.
On the other hand, since the diameter of medusae's mouthlets remains unchanged throughout the medusa stage, their food is confined to micro and mesozooplankton that can pass through these openings. Examination of the gastric pouch content of wild medusae revealed that copepods were usually the dominant food items, and occasionally many fish eggs were also eaten.
Polyp and medusa, names for the two body forms, one nonmotile and one typically free swimming, found in the aquatic invertebrate phylum Cnidaria (the coelenterates). Some animals of this group are always polyps, some are always medusae, and some exhibit both a polyp and a medusa stage in their life cycle.
The polyp is a sessile, or nonmotile, organism; well-known solitary polyps are the sea anemone and the freshwater hydra. The medusa, when free swimming, is popularly known as a "jellyfish".