On his famed trip around the world on the H.M.S. Beagle, Darwin collected many crustaceans. When he returned, the collection was scattered and partly lost. But here is just one crab collected by Darwin himself, one of many from Oxford collection of Darwin’s crustaceans:
Darwin’s crab collection recently went on tour to Australia.
Crustaceans are mentioned in the Origin:
(E)ven the illustrious Cuvier did not perceive that a barnacle was, as it certainly is, a crustacean; but a glance at the larva shows this to be the case in an unmistakeable manner.
It is no accident to find reference to barnacles, since Darwin had some years earlier published major monographs on barnacles, a plate from which is the second Tuesday Crustie, which shows some of the larvae that showed that barnacles were crustaceans:
Description of the plate is here. For comparison, here’s a live one, taken from here:
Darwin spent years trying to sort out the barnacles. Jonathan Weiner argues in The Beak of The Finch barnacles forced Darwin to confront the problem of variation, and the difficulties of determining what is a species and what is merely a “variety.” And it was not an easy task, as indicated in the title of this post, which was taken from a letter Darwin wrote to W.D. Fox.