Cyamis boopis is one of the cyamidae better known as a whale louse.
This particular species is from Scandinavia, as illustrated in the book An account of the Crustacea of Norway, with short descriptions and figures of all the species by G.O. Sars – specifically the second section of Vol. 1, which is where the illustrations started.
You can tell this guy is designed for clinging onto a streamlined surface as it travels at speed. They’re only around 8 to 10 millimeters long, and hang out with barnacles near the genitals of whales. Fun fact from Wikipedia: “Whale lice will promptly try to attach themselves to people when handling whales during processing.” Hard to say whether it’s the attempted attaching or the “processing” that’s the more horrifying image.
They’re not especially harmful to whales, though, living mostly on algae that grows on the whale’s skin and flakes of dead skin itself. Little dandruff-eaters.
The book is from the Biodiversity Heritage Library collection, which if you haven’t heard, could use some help keeping the lights on what with the rapid, um, “reallocation” of federal funding for educational pursuits.