Thanks to all for the information.

Using David's description, I would say that the few, old, elongate valves that I
have encountered in this stream may have been Unionids. The valves were broken
and little more than an inch across. Also, they seemed rather thin and fargile.

The live specimen that I mentioned initially plus a second, smaller one of the
same variety are the ONLY live bivalves that I have seen here. These were no
more than an inch or two down in the clean gravel bed near the center of the
stream. The current was easily two to three knots.

Considering the Zebra mussel problem coming down from the Great Lakes, I wonder
if one is allowed to "disturb or molest" introduced species such as this one.

Aloha,

Bob Dayle

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>
> --- "Dr. David Campbell" <[log in to unmask]> escreveu:
>
> > > I was wading in the local creek (central Indiana) when I
> > noted a
> > > single valve in
> > > the foot-deep water. Hoping to stir up its mate, I came up,
> > instead,
> > > with a
> > > live clam. At a mere 3/4-inch across, it was rather
> > small,... to
> > > someone who
> > > has seen three foot wide Tridacna gigas in situ.
> > >
> > > Since it is illegal in this state to disturb or molest ANY
> > mollusk, I
> > > tossed it
> > > back after noting that the valves were dark brown at the
> > hinge but
> > > quickly gave
> > > way to an algae-green color other the rest of the shell. I
> > estimated
> > > about 15
> > > "growth rings" on it.
> > >
> >
> > Sounds too big for a sphaeriid (fingernail clam).  If the
> > "growth
> > rings" were regular concentric sculpture, then you had
> > Corbicula.
> > Despite most of the literature, the main species of Corbicula
> > invading
> > the U.S. is probably C. leana.  A second species is known only
> > from
> > the southwest (also invading Europe and South America), which
> > may be
> > true fluminea (of which manilensis is a synonym).
> >
> > Unionids may show bands of color or weak irregular growth
> > lines, but
> > no regular concentric sculpture in our species.
> >
> > As sculpture rather than growth rings, they form fairly
> > quickly and
> > without direct connection to environmental factors.  Tiny
> > juveniles
> > already have several concentric ribs.
> >
> > Corbicula range from oval (not very elongate) to nearly
> > triangular in
> > some large old individuals in lakes.  Most unionids are more
> > elongate.
> >
> > --
> > Dr. David Campbell
> > 425 Scientific Collections Building
> > Department of Biological Sciences
> > Biodiversity and Systematics
> > University of Alabama, Box 870345
> > Tuscaloosa AL 35487-0345  USA
> >
> >
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