Periphylla periphylla Peron and Lesueur, 1809, equatorial Atlantic Ocean.
OTHER COMMON NAMES None known.
These medusae have a conical swimming bell that is up to 8 in (20 cm) tall and 6.5 in (17 cm) in diameter, but specimens from oceanic waters usually are less than 2 in (5 cm) in size. The bell of small specimens is transparent and reveals the reddish brown stomach. In large specimens, the bell is opaque and maroon in color. The bell has a pronounced groove with 16 deeply notched lappets beneath it. Twelve thick tentacles emerge from the bell surface above the clefts, in a repeating pattern of three tentacles and one rhopalium. The stomach is baglike. Oral arms and the polyp stage are lacking.
This species is found at mesopelagic depths in all oceans worldwide. Populations that are several orders of magnitude greater than they are in the open ocean have been found in Norwegian fjords, especially Lurefjorden.
The crown jellyfish generally is found at depths below 3,000 ft (900 m), where water temperatures remain a cool 45°F (7°C) or less all year. At high latitudes they inhabit shallower depths, 650-1,300 ft (200-400 m) in the daytime and from the surface to 650 ft (200 m) at night.
These medusae undergo vertical migration from deepwater in the daytime to shallower depths at night, presumably following their prey. Exposure to white light causes rapid downward swimming. As with other deep-dwelling coronate medusae, when they are disturbed, the bell and ovaries are brilliantly bioluminescent. They also produce copious amounts of luminescent mucus that contains stinging cells.
The natural behavior of medusae was observed with red light and video cameras on a Remotely Operated Vehicle (ROV) in Lurefjorden, Norway. The medusae hold their tentacles up alongside the bell or at right angles to the bell. They swim downward for about 30 ft (10 m) and then drift upward. The tentacles sometimes quickly arch toward the mouth, coil, and enter the stomach. Few prey (copepods, ostracods, and chaetognaths) were found in ROV-collected specimens. These
I Cassiopea xamachana I Periphylla periphylla medusae have low metabolic rates and apparently survive on few (less than 35) prey items daily.
Fertilized eggs are released in deepwater, where they drift, not feeding for several months. Eggs and larvae are present all year in Lurefjorden, suggesting lack of seasonality in the relatively constant environment of the deep ocean. The larvae develop directly into medusae without polyp or ephyra stages.
CONSERVATION STATUS Not listed by the IUCN.
In Lurefjorden the crown jellyfish may have nearly excluded small fish, which are common in other fjords. There are possible medical applications for the bioluminescent proteins. Deep oceanic populations have no apparent significance for humans. ♦
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