This is an illustration of a sea creature that, at the time, was (not exactly) new to science. It was new to British science when C. Spence Bate wrote about it in “On a new genus and several new species of British Crustacea” but nowadays, we call these critters Haustorius arenarius .. the name given to ’em in the 1700s by a Dutch fellow named M. Slabber.
They’re a kind of amphipod, a crustacean that crawls around on and under the sea floor.
I found the illustration, and Bate’s article, here, in the Biodiversity Heritage Library.