Marine Pea crabs (Dissodactylus primitivus) are mobile little creatures that can parasitize two different urchin host species. Although their developmental life cycle takes place on the red heart urchin (Meoma ventricosa), adult pea crabs can move around to their other host species, Plagiobrissus grandis urchins. Adult pea crabs switch between hosts quite often due to factors such as competition, disease, or mate searching but they are found more frequently on their original hosts. Scientists have demonstrated that pea crabs can find their red heart urchin hosts by smell. What’s more, pea crabs found on read heart urchins show a preference for this host when given the choice, but pea crabs found on P. grandis urchins show no preference in choosing between host smells in an experimental y-maze. These preferences (or lack their of) may explain why adult pea crabs are unevenly distributed among their two hosts.
Sketch contributed by Melissa Jones. Fact contributed by Adrian Perez.
Source: De Bruyn, C., De Ridder, C., Rigaud, T. and David, B., 2011. Chemical host detection and differential attraction in a parasitic pea crab infecting two echinoids. Journal of experimental marine biology and ecology, 397(2), pp.173-178.