Periphylla periphylla are deep-sea medusae with twelve stiff tentacles, which extend from a thick, bell shaped body. These animals have dark red and/or brown stomachs, and are bioluminescent. They can be up to 20 cm long, and their bodies, or central domes, have a diameter of up to 35 cm. The coronal groove, located on the lower portion of the bell, helps to contain prey, and also provides flexibility for movement. The coronal groove divides the aboral surface into the central dome and the peripheral zone, which contains radial thickenings called pedalia and marginal lappets that contain some sense organs. This zone also contains the tentacles, which are useful in moving prey to the mouth. The mouth is very simple and is located on the manubrium. Externally, males and females of this species are similar. No indication of geographical or seasonal variation was reported.

The pigment that gives P. periphylla their red-brown color is protoporphyrin (also known as porphyrin), which can lead to tissue damage as a result of photosynthesis. The pigment is not harmful to this species as they do not usually stay in shallow waters.

Periphylla periphylla contain relatively high levels of lactate dehydrogenase, an enzyme important to anaerobic metabolic functions. This is likely useful for movement in ocean layers with minimal amounts of oxygen.

The Q10 value of an organism is its temperature coefficient- the factor of change in respiration caused by an increase in temperature of 10 °C. The value for P. periphylla, calculated in the range of 5°C - 10°C, was found to be 2.6. This value indicates that temperature affects the biochemical reactions of the organism. A value of 1 would mean that the organism is insensitive to temperature.

The water content of P. periphylla is 95.7 - 96.6 percent of the total wet weight. The measured salinity of the surrounding water when this was measured was 33.1-33.3 percent.

Periphylla periphylla are one of the only five scyphozoan species that is bioluminescent. The bioluminescence, along with with its red-brown coloring and the direction of its tentacles, make it easy to distinguish. The blue or blue-green light emission occurs as a result of stimulation and is concentrated in specific parts of the organism, such as the marginal lappets and near the coronal groove. Members of these species exhibit bioluminescence as a response to a short pulse of alternating current with a series of flashes.

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-Animal Diversity Web