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.
|