When Himasthla species B meets the California horn snail, things get ugly. The body snatching flatworm invades the snail's gonads, starts breeding, and eventually takes over the mollusk's entire body, foraging, eating, and growing along with it. Now researchers have found an even more impressive Himasthla trait: a surprisingly complex social structure. Reporting online tomorrow in the Proceedings of the Royal Society B, a team finds that Himasthla colonies are divided between a class of reproducers that are large and sluglike, and a soldier class that have skinny bodies, huge mouths, and never reproduce. The soldiers viciously defend the colony from other flatworm groups or species that would take over their host, swallowing enemies whole (as seen above). This caste system puts flatworms in the company of animals renown for their complex societies, such as termites and bees. Not bad for a creature with just a couple of ganglia for a brain.
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