Mytilus trossulus Gould,  is an interesting species: although it is
generally more elongate and thinner-shelled than edulis, it is nearly
impossible to reliably differentiate the two on conchological features
alone, since they overlap in form: edulis is an extremely variable
species.  They CAN be told apart via an enzymatic test, but this is not
a practical method for most collectors!!  In the Maritime Provinces of
Canada, this species was not recognized until the late 1980s, when it
was noticed by mussel farmers that some of their crop was thin-shelled
and more susceptible to breaking during washing with powerful hoses.
So, a BYM with the Dept of fisheries was put on the case, and he figured
out that most of the thin-shelled critters were in fact a separate
species (trossulus), which could only be reliably separated from edulis
by the prescence of a certain enzyme - the details of which i have
forgotten.
        Anyway, i have not heard about anybody reporting either trossulus or
galloprovincialis (which has not been found on the east coast) from
western Canada, although since none of the local universities has seen
fit to subscribe to the Zoological index since 1995, most of the
malacological goings-on with the local fauna have eluded me, since i
can't afford on-line searches.  if only there was a place to borrow this
pricey - but-fabulously-useful reference book from via mail...... but
that's about as likely to happen as the world becoming nuke-free anytime
before the next major war!!

From the land that the rest of Canada would like to forget about sometimes,
Ross Mayhew.

Peter Egerton <[log in to unmask]> wrote:

Hello all,

I just finished collecting a batch of mussels here in Vancouver
and have been reading up on our species here in British
Columbia. I'm getting a little discouraged re identifying what
I have here. Can anyone shed some light for me on the most
recent views about west coast mussel identification. Do we
have Mytilus trossulus, M. edulis, or M. galloprovincialis or
a combination of the three. Is there a way to distinguish which
species one is looking at?

Thanks for any help,
Peter