Symbiotic barnacles for underwater respiration

My world has two races of mammalian mermen, one of which are somewhat monstrous and I'll call them "Abyssals" in this thread. I really want the Abyssals to 'breathe' underwater, as well as being able to walk on land, so as a rule they have to have recognizable human anatomy like two strong legs rather than a fish tail. Also, I want this to be the result of evolution rather than mystical creation or genetic engineering, so I'm not so hot about radical changes like giving them gills.

I had an idea that they should be covered in barnacles and similar parasites, and building on that, maybe some of these parasites have become symbiotic. One species (doesn't have to be barnacles) has developed a sort of intravenous connection with the host mammal, so that it transmits oxygen into the Abyssal's blood, that way the Abyssal can remain underwater for longer, which allows the IV-barnacles more access to food, assuming they don't just feed on the Abyssal's blood.

How plausible is this symbiosis? If one Abyssal is covered in about a hundred barnacles, would it allow the Abyssals to remain underwater indefinitely, or only extend the amount of time before they need to surface for air?

posted over 5 years ago

Maddock Emerson‭

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