Aurelia labiata Chamisso& Eysenhardt, 1821, top 2 photos; Aurelia aurita (Linnaeus, 1758), third : Moon Jellies  
Phylum Cnidaria / Class Scyphozoa / Order Semaeostomeae / Family Ulmaridae
Moon jelly, Aurelia labiata, Carmel Bay CA, Pacific Ocean
Moon jellies, Aurelia labiata, Class Scyphozoa, Carmel Bay CA, Pacific Ocean

Moon jellies differ from other large West Coast scyphomedusae in that they lack the long, potent stinging tentacles that people generally associate with jellyfish. Instead, the moon jelly may capture food on the surface of the bell using mucus to ensnare zooplankton prey. Cilia transport the food to the bell margin and tentacles, where it is passed to the frilly, conical manubrium. With its high surface area, the manubrium also probably functions directly in the capture of prey. The 4 horseshoe-shaped stomach pouches are readily visible at the top center of the bell, as are the purplish gonads immediately beneath. When a moon jelly has had a hefty meal, it’s easy to see food packed in the stomach pouches. Hundreds of fine, relatively short tentacles line the bell margin. The sting of this jelly is mild and most people have only a minimal reaction to it, if at all. The bell is a striking translucent white, diameter up to 40 cm, and may be tinged with pink or lavender. It is marked by 8 lobes, each with a notch so that there appears to be 16 lobes, and 8 rhopalia. Sexes are readily distinguished since females hold the fertilized eggs, which appear as whitish-gray clumps on the manubrium (last photo). Males may sometimes be seen with long sperm filaments trailing from the oral arms.

In Monterey Bay large surface aggregations may be seen during fall and winter months when they can be quite abundant (photo 4). During other periods moon jellies may not be seen for many months. Aurelia labiata inhabits nearshore surface waters from southern California to southeast Alaska. A similar species (A. aurita; 3rd photo) has been introduced to San Francisco Bay and perhaps other West Coast areas. It has 8 bell lobes that lack the notch characteristic of A. labiata, a distinctly smaller manubrium, and oral arms that extend beyond the bell margin (the oral arms in A. labiata do not typically extend beyond the bell margin). This is a common jelly in Europe where it probably originated, and may also now be found off Japan and the U.S. East Coast, and in the Gulf of Mexico.

It is relatively easy to establish polyps and culture Aurelia in captivity. The medusae can successfully be maintained in a variety of aquarium systems. A. aurita is probably the most commonly displayed jelly at public aquariums, and is the species that most neophyte jellyfish aquarists start with.

Aurelia labiata, video courtesy of Patrick Anders Webster, Pt. Lobos CA, January 2014

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