This jellyfish has two life phases, a polyp form and a medusa form, each giving “birth” to the other.
The polyp is tiny and sessile (attached to a surface; not free-floating), like a very simple sea anemone or hydroid with only a few branches. The polyps form buds on their sides that separate to become new individuals. In this way, the polyps can form in colonies.
Most of the year, this jellyfish species is usually present only in the polyp form (or in a dormant, tiny, seedlike resting form called a podocyst). These are little seen or noticed, but they tolerate a wide range of temperatures.
The free-swimming medusa phase has the typical jellyfish form: an umbrella-like body with a stomach (manubrium) extending downward from the center. At the bottom of the manubrium is the mouth opening, with 4 frilly lobes. A fringe of up to 400 tentacles lines the edge of the “umbrella.” This creature is transparent or translucent, sometimes faintly tinted tan, gray, white, green, or blue. Four white, opaque patches sometimes appear in the body; these are the gonads (organs that produce sperm and eggs).
Although in our state the medusa form only occurs during mid to late summer, when surface waters reach about 80F, it is nevertheless the most commonly seen phase of this animal, due to its size and location near the water surface.