Andrew,
 
I think the answer depends on what you really mean by "recognizing a
species". Does the person have to know the name of a specimen or is it enough
that the person recognizes a specimen as a described species? A person who
works with molluscs (or any other taxon) may be able to recognize a large
number of different specimens as described species without necessarily
remembering their names. There may be different memory processes going on in
the brain. One is simply the recognition of a familiar object. The other
involves the linkage of a recognized object with its name.
 
A.