Whelk is the common name given to various varieties of sea snails.
In Britain, it usually refers to an edible species known as Buccinum undatum, also known as the northern whelk or the common whelk.
Whelks have been, and sometimes still are sold from stalls at the seaside alongside other seafood such as cockles, mussels and prawns.
The phrase 'not fit to run a whelk stall' is sometimes used as a derogatory description of someone perceived as useless.
Follow this link to see a London whelk stall (c.1910).