NEMERTEAN PREDATION ON THE TROPICAL FIDDLER-CRAB UCA MUSICA

We saw 79 predatory interactions between a new species of monostilifer ous, suctorial hoplonemertean and the fiddler crabs Uca musica (77 cas es) and U. stenodactylus (2 cases). At an intertidal sand bar in the P acific entrance of the Panama Canal, worms ate about 0.1% of the adult crab population per day. The mode of attack and the spatial and tempo ral distributions of interactions suggest the worm is an ambush predat or. When struck by a worm's sticky, mucous-covered proboscis, crabs pr oduced copious foam from their buccal area. Mucous-laden crabs that es caped, again foamed indicating that the foam may counteract the mucus. If the attack led to a kill, the struggling crab soon became quiescen t, as is typical in other nemertean-prey interactions. The worm invert ed its proboscis, found ingress to the crab's body and fed. Crabs esca ped by autotomizing appendages entwined by the proboscis, by forcefull y pulling away and by remaining quiescent, then moving away when the w orm inverted its proboscis and before it entered the crab. Immobility, a response to visual predators, may falsely indicate paralysis to the worm and cause it to invert its proboscis, thereby providing the crab with an opportunity to escape. This predator-prey interaction seems t o incorporate generalized predator tactics and fortuitous prey defense s that give worms and crabs about an even chance of success.