Great idea Andrew.   I wonder if (after boiling)
while pliable one coated at least one side of the
operc with glycerine, might it remain flexible?

Congrats on your new acquisition, by the way!  ;)



Nancy Smith




|]      -----Original Message-----
|]      From: Andrew Grebneff
|]
[mailto:[log in to unmask]]
|]      Sent: 28 January, 2004 2:06
|]      To: [log in to unmask]
|]      Subject: Oversized opercula... and how to
fit them
|]
|]
|]      If anyone has pondered a shell with an
operculum which
|]      just CAN NOT
|]      fit into the aperture, the answer is this.
|]
|]      The dealer probably has not supplied the
wrong operc.
|]      Most gastropods
|]      have opercs which fit reasonably well in
the aperture; in some
|]      species it more-or-less blocks most of the
aperture,
|]      possibly leaving
|]      the canal unsealed. In others (Turbinidae)
it
|]      hermetically seals the
|]      shell. In some it is far too small to
seal.
|]
|]      Well, in some Calliostoma (eg NZ's C.
selectum, C.
|]      waikanae and other
|]      members of this superspecies) and
Entemnotrochus the
|]      operc, if dried
|]      flat, is far too big to fit. For instance,
in the 194mm
|]      Entemnotrochus rumphii I just bankrupted
myself on, the
|]      aperture is
|]      56mm high... the operc is about 66mm high.
The operc
|]      was supplied
|]      out-of-shell, dried loose, so that it
curled somewhat.
|]      No way would
|]      it fit, even warped.
|]
|]      These opercs act as a diaphragm. When
living the operc
|]      is saturated
|]      with water and is soft and flexible. When
the animal retracts it
|]      drags the operc right in with it, and the
operc bends,
|]      thoroughly
|]      sealing the shell. I have observed this
with plenty of the
|]      Calliostoma named above.
|]
|]      The trick with these is to boil the operc
until it is nice and
|]      pliable, fill the aperture with cotton,
then align the
|]      operc (with
|]      leading growth edge at the outer top of
the aperture)
|]      and push it in
|]      so that it sinks in evenly. Then allow to
dry in place.
|]      Worked fairly
|]      well with the big pleurotomariid, though
the edges have
|]      curled a bit
|]      and it's now a bit loose.
|]
|]      Those pleurotomariids with
seemingly-too-small opercs,
|]      as well as
|]      turritellids, have evolved a tactic to
avoid
|]      crab-peeling predation.
|]      These animals retract far up into the
shell, past the
|]      point where any
|]      crab can break back the shell wall. The
operc probably
|]      seals fine at
|]      this point.