Pelagic Barnacles on Egg-yolk Jelly

Pelagic barnacles (Family Lepadidae) will attach to just about anything floating in the open ocean.  One species, Alepas pacifica, has taken things a step further and sets up shop on the bells of large jellies, such as egg-yolk jellies (seen here in the photo), purple-stripe jellies, and at least 5 other scyphozoan species.  Typically the barnacles, which may occur singly or in clumps of up to 8 to 10 individuals, are attached at the top of the bell in the center.  To lighten the load on their gelatinous host, the hard shell component characteristic of other barnacles is very thin and reduced.  It's hard to say whether the jelly is harmed by it's crustacean hitchhikers, but once attached, there's not much it can do.  With certain scyphozoan species, it appears that the barnacles are parasitic, feeding on gonadal tissue of the jellyfish.  Most large jellies however do seem to avoid the extra load - it's relatively uncommon to see an egg-yolk jelly wearing a pelagic barnacle cap.      

 All photographs in the JelliesZone © David Wrobel and may not be used or copied without permission!