Paul,

I have not really seen anything on Nerite opercs to the detail you require.
Most of them do have a proteinaceous strip around the outer rim.  This is
normally around what is thought of as the top if looking at the operc with
the apophysis pointed down.  This strip is often narrow in Nerita and quite
wide in Neritina and Clypeolum.  Others like Clithon, Vitta, and Vittina
fall somewhere in between.  This strip is often missing from the opercs in
collections as it is quickly dissolved in bleach and even if preserved, it
is thin and fragile.  Once dried it easily beaks away.  In life, this strip
acts like weather stripping and provides an air/water/collector's pointed
tools tight closure.  On some species (N. japonica) this strip encircles
just about the entire operc.

As for the layers, I have also noticed the layers, but there is no single
standard and I do not think there is a central conchiolin layer.  If you are
looking at the operc from the top, the thin proteinaceous strip (often worn
away flush with the edge of the operc) will look like your central horny
layer.  However, if you break the operc in half I do not believe you will
find the same layer.  Nerite opercs seem, for the most part, to be
calcareous, through and through.  There are layers and on many older
specimens, the outer granulated layer (on say a common N. undata) will flake
off leaving a smooth surface.  Come to think of it, I have never seen this
with N. undata, but I have with N. insculpta and some others.  Some species
(Clypeolum oweniana) have a periostracal covering over the face of the operc
(both sides).

My two cents,

Tom Eichhorst in New Mexico, USA (spending the day trying to figure out the
differences between Nerita insculpta, Nerita georgiana, and Nerita scripta
(a synonym I think)


Hello folks,

I just discovered something I never knew before (at least I think I did) and
I am wondering if anyone can confirm this.  I was photographing some
opercula for a presentation I am doing next week at the local shell club
meeting.  I wanted to make the point that all opercs have a conchiolin base,
even though some of them subsequently add a calcareous layer.  So I was
looking through my shells to find some good examples of calcareous opercs
with the inner conchiolin layer still present.  Turbinidae - no problem.
Naticidae - no problem.  But after looking at a hundred or so Neritidae
opercs, I could not find a single one with the inner surface covered with
conchiolin.  However, some of them did seem to show a bit of corneous fringe
at the margins.  I then started looking at them on edge, under the
microscope, and many of them have the appearance of a sandwich - calcareous
on both sides, with a (presumably) conchiolin layer in the middle??  I
theorize then, that moon snails and turbans calcify only the outer side of
their opercs, while nerites deposit calcium on both the inner and outer
surfaces.  However, I don't remember ever seeing this in print.  Can anyone
confirm this?  Or am I misinterpreting things here?

On another subject, [log in to unmask] no longer exists.  Well, PaulCyp does,
but home.com does not.  I am now [log in to unmask]

Regards,
Paul M.