YECH!  I didn't know humans anywhere ate brachipods!  No surprise I guess,
they eat just about everything else that comes out of the ocean.  The amount
of edible material inside a brachipod shell is small though, compared to a
clam of the same size.  Your apt description (look like fingernails, with a
worm coming out of them) suggests the branch of Brachiopoda called
Inarticulata.  They have a semi-flexible, translucent shell, with a thick,
worm-like stalk protruding.  Collectors are more familiar with the other
branch, Articulata, which have a rigid shell, more closely resembling that
of a bivalve mollusk, and a thinner, shorter stalk.  The specimen Thomas
Clenche posted is of this type.  In the Inarticulata, there is no hinge, and
the valves are held together only by the soft tissues of the animal.  But in
the Articulata there is an interlocking type of hinge (sort of like that of
Spondylidae), which only allows the valves to gape about 10 to 15 degrees.
To open the shell wider than that, you have to force and break the hinge.
However, it's pretty easy to pull the soft parts out through the narrow gap
with a pair of thin forceps because, as I indicated above, there isn't much
to the soft parts.  On the other hand, many articulate brachiopods have a
thin, loop-like extension of the shell interiorly (which supports the
lopohophore, the large feeding organ), and it is very difficult to remove
the soft parts without breaking that structure.

Paul M.