"We used to have a chancre for supper of a Saturday night..."

...when we came home from Town.  It was cooked on the Friday in the copper in the wash-house.  It gave a scream when it was dropped in the hot water..."

To anyone with a medical background or a general familiarity with infectious diseases, the first phrase of that sentence would give a shudder.  I found it in Chapter 3 of G. B. Edwards' The Book of Ebenezer Le Page.  My dictionaries - including the O.E.D. - offer nothing but venereal disease definitions for "chancre."

The book is set on the island of Guernsey, off the French coast, and the narrative is peppered with French terms.  When I type "chancre" into Google translate, however, all it offers is canker/chancroid/plague.

From the context, the "chancre" should be a shellfish, and I'm betting that the etymology is related to the Latin "cancer" for "crab" and that the chancre is a crab of some type.  But why can't I find the connection?  Is it perhaps a local dialect of the Guernsey region?

Perhaps one of my Francophile readers can help out on this one.

Update - Once again, no question on this blog goes unsolved.  First someone found this - "The edible crab is also sometimes referred to as the Cromer crab, because it is commonly caught around the Norfolk coastal town of Cromer. In the Channel Islands languages of Dgèrnésiais and Jerriais, it is called a chancre."

And then Dominique found -
Crabe chancre - Callinectes bocourti at this link, and
Crabe verruqueux - Eriphia verrucosa at this link, which provided the photo above, and offered the photo below re etymology (from the DMF, Dictionnaire du Moyen Français)

Now I won't be afraid to order a chancre if I ever get to Guernsey.  Merci.