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Today on Animal Fact Files we’re discussing parasitic barnacles. I'm sure many of you have seen the parasites that take control of another animal's body, like liver flukes in ants or flatworms in snails, but did you know there are barnacles that do this, too? I didn't until learning about the goose barnacles we discussed in a previous episode, and I felt the need to share this information with you all!

Like all barnacles, parasitic barnacles are crustaceans, but you wouldn’t gather that by looking at one in its adult stage. Adult parasitic barnacles don’t shed their exoskeleton, don’t have segmented appendages, and almost completely lack internal organs. In fact, unless you saw a parasitic barnacle in its larval stage, you may not even think they could be crustaceans. The adults are ooey, gooey, and fully taking over another animal’s body. Fascinatingly, parasitic barnacles almost exclusively parasitize other crustaceans, including other barnacles!

These arthropods begin life as an egg and hatch into pelagic larvae. They drift through the water column looking like any other barnacle larvae, that’s how scientists know they’re related! The larvae don’t eat as they don’t have a mouth, and they pass through several stages, shedding their exoskeleton as they grow. Eventually, sometimes weeks later, sometimes months later, a female larva settles onto an unsuspecting host. Like other barnacles, she uses a cement-like paste to hold her in place. She jabs needle-like appendage through the host’s body, often into the gills, and squishes herself inside. This stage is known as the 'vermigon'. She grows a root system which winds its way through the host and absorbs nutrients. Outside, a sac-like structure takes over the host’s lower abdomen and connects to the roots via a stalk. Supposedly, this pulsates frequently. Once fully in place, the parasitic barnacle is now an adult. Since parasitic barnacles have a preference for crabs and other decapods, and they don’t kill their host, they can live there for quite some time.

All right now back to the male. When the female is fully formed with her mushroom-like sac hanging off the host’s abdomen and her mycelium-like roots running through its body, the male larvae is attracted to her via pheromones. Like a deep sea anglerfish male, the male parasitic barnacle makes his way to the female and through a process of more jabbing things in places and burrowing into her body, he becomes a parasite to her giving her access to sperm in order to fertilize her eggs. A parasite in a parasite! Who knew?! The number of males a female can host depends on the type of parasitic barnacle.

Fascinatingly, most parasitic barnacles can make their host completely stop shedding, or be unable to reproduce at all. If a female settles on a male crustacean, she can make the male host behave like a female brooding her eggs, though instead he’s brooding his own personal parasite. There are currently over 250 described parasitic barnacle species and they range from the depths of the ocean to freshwater environments. Some are even semi-terrestrial. They live just about anywhere they can find a suitable host!

For more facts on parasitic barnacles, check out the links below. Give a thumbs up if you learned something new today. Thank you to our Patrons SpikeSpiegel93, Dad, and everyone else for their support of this channel! And thank you for watching Animal Fact Files!