Each species in Shedd’s Jellies special exhibit has some stunning attribute that sets it apart from the others and makes you stop and look. The purple-striped sea nettle is a study in contrasts. The silver-white bell has 16 deep red rays that will darken to purple as the jelly matures. Between the rays are fine speckles in a similar hue. From the inside center of the large bell, four ruffled white oral arms can trail a foot or more while eight maroon tentacles hang down like ribbons from the bell’s edge.
The stripes on the bell make it easier to picture the inner workings of jellies. Small planktonic prey are zapped by the stinging cells on the tentacles and then carried along the tentacles and oral arms into the jelly’s stomach. Digested nutrients course through the body in tubular canals associated with those colorful rays on the bell. What isn’t digested goes back out the way it came in, through the mouth.
But there’s more going on under that bell. Some juvenile fishes like to swim under the protective canopy of a large purple-striped sea nettle, where they’re safe from predators. And despite its venomous stings, this species attracts hitchhikers. Larval and juvenile cancer crabs live on the bell and oral arms of this jelly, impervious to its stinging cells. Scientists aren’t sure whether the crabs feed on parasites that could damage the jelly’s tissues or if they actually eat the jelly.
Other animals also appear to be unfazed by the nettle’s toxic stings: Blue rockfish, ocean sunfish and harbor seals have no problem making meals of purple-striped sea nettles.
Posted by Karen Furnweger, web editor