This close up of whale skin shows a community of living creatures. Gray
Whales have two common hitchhikers on their bodies: barnacles and whale
LICE.
But whale lice aren’t lice at all; they’re a type of
amphipod crustacean called cyamids. And each species of cyamid is unique to a
species of whale! To survive, cyamids hitch a ride on a whale and munch
bits of its skin and flesh. If the whale is healthy these parasites
don’t harm it – a commensal relationship. If a whale is covered in them
it is often an indication of illness or injury.
Barnacles like these feed only on plankton, by reaching their fuzzy legs out through the opening on top! Whale barnacles sink down into the whale’s skin over time, but the skin is so thick the whale will never even notice, and interestingly enough, some whales seem to have rougher patches of skin that serve no immediately obvious purpose other than to make it even easier for barnacles and lice to attach.
In right whales, this is because the pale lice and barnacles contribute to the bright patches the whales may use to visually distinguish one another, and could have additional benefits we haven’t even considered!.
Harmfully parasitic barnacles do exist, but almost all of them are (AMAZING!) internal parasites of other invertebrates, with just one grisly exception:
Anelasma are a group of goose barnacles that have become parasites of tiny, bioluminescent deep-sea sharks. Goose barnacles are usually filter feeders, like the acorn barnacles, but distinguished by a long, fleshy stem.
In Anelasma, the legs are too reduced to gather plankton and the mouth no longer functions, if there’s any mouth at all. Instead, the stem has evolved into a “bulb” and “roots” that penetrate alarmingly far into the shark’s body. When a new larval Anelasma finds a shark, it follows the scent of any Anelasma already there, resulting in these disturbing clusters of them – there are three in this image.
This shark was lucky that its first barnacle didn’t decide to settle down somewhere worse, here’s a dead bastard who wound up with a pair of “horns:”
Sometimes a cluster is also found where a shark used to have an eyeball, or growing inside the mouth until it would have been unable to feed.
This is also the only parasite that intentionally castrates a vertebrate host in order to hog more nutrients for its own reproduction, something you more commonly see in the parasites of insects and mollusks,
ifesbob 