Quoting Tom Eichhorst <[log in to unmask]>:

> Spring is a good time to be in Calgary.  I spent two years just a bit
> north of there in Edmonton with lots of trips further north (all the way
to Alert if you happen to look for it).  Andrew, I would advise warmer
climes before October.

Indeed... I will be here until early midJuly. I lived in Edmonton 1961-67.

> Septaria seem designed to handle strong
> currents and are indeed often found in such, but like Andrew mentioned,
> can
> be found in turbid conditions.  There is some evidence of a difference
> in
> shell shape in different water types.  This certainly is the case
> concerning
> where they habitually rest with those on reeds and other plants along
> the
> water's edge are much more elongated (enough to garner a few
> synonymous names).

I found a size difference also... specimens on the river clam Batissa
violacea which I saw in markets had the occasional septaria attached.
These never reached more than 1cm in max dimension and tended to be ovate
rather than trapezoidal in outline.

One of the reasons I believe they are easier to lift from the
> substrate than a similarly sized limpet is the septa from which they
> get
> their name.  This is formed across the lower portion of their body
> (where
> the columella would be if they were a standard coiled snail).

I would consider the axial edge of the aperture to be a columella, though
in neritids the carbonate in the region of the columella seems to be
resorbed and redeposited as a shelf.

I believe the internally-located but large calcareous operculum of
Septaria is a muscular attachment allowing the animal to produce a greater
grip than would be the case if the operc was absent.

Regards
Andrew

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