Limicolaria epiphragm

[brunni]

A friend of mine recently visited Gabon and collected a few Limicolaria shells. Two of them were albinos ( making species identification difficult) and although the specimens were dead collected one of them still had a callous plug in situ.
During dry periods many snails seek refuge under detrius or bury themselves in the ground. To prevent moisture loss the Limicolaria produce a thickened plug to seal their aperture. This is known as an epiphragm ( see : en.wikipedia.org/wiki/Epiphragm )
Here is the shell 37.4mm long. It was collected under detrius and sand in a coconut plantation at Ombouè, near Lac Feràn Vaz in Gabon. The plug is clearly visible ( though slightly "ajar" ) !

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[brunni]

Here's a bit more detail on the epiphragm, seen from internal and external point-of-view. It is extremely fragile and cracked when I just looked at it ! Size approx. 14.5mm x 9.5mm

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[coyote]

Very interesting. My Cantareus apertus also produced a calcareous epiphragm. It was quite startling to see it the first time, since none of the other species I'd ever kept formed such epiphragms. I was used to seeing the papery, mucus seals instead.

[brunni]

It is indeed interesting how nature finds a solution to propegate species, in this case prevention of moisture loss.

[coyote]

I am surprised that some species use a calcareous epiphragm in the first place, since calcium is so vital to its own shell health and to egg formation. I wonder if species with this kind of epiphragm have evolved in areas with sufficient extra calcium in their environment that some could be successfully diverted to forming the epiphragm.

[brunni]

I have been googling up some info to try and find a sensible answer when I stumbled on this :

"Under dry conditions, land snails withdraw into their shells closing the entrance with a calcified mucous membrane called an epiphragm and become dormant (aestivate). In this state, the partial pressure of oxygen gradually falls to low levels whereas the partial pressure of carbon dioxide rises."
( source : www.ajol.info/index.php/br/article/view/28549 )

So achatinid aestivation not only preserves moisture, the epiphragm deters predators ( e.g. ants and beetles ) and assists the animal to enter a state of entire quiescent during which it hardly breathes ( don't forget the pulmonates have gills and breathe air ). ;D

[brunni]

Coyote ! your Cantareus apertus and my Limicolaria, are (like most of the land snails ) pulmonates and as such do not have a permanent trapdoor to close their aperture. During times of hibernation ( too hot, too cold, too dry ) some of them are able to produce from their mucus a seal which hardens as it dries to close their aperture. I mentioned some of the reasons for the seal in my last post. It is a temporary structure and as it is brittle; I also suspect it may easily disolve in water. It may contain some kind of calcium though I'm not yet sure on this. It is called an epiphragm.

This is in contrast to the bulk of the marine and fresh water mollusks, and some of the landsnails, that produce a permanent trapdoor and belong to another subclass, the prosobranchs. Their door is called an operculum ( one operculum, two operculae ) and it is fixed on top of the rear part of the snail's foot. When the animal retracts into the shell the door is closed ( maybe sleeping, or times of stress or defense ), and when its hungry it opens the door. The operculum may be thin, slightly flexible and horny or hard, rigid and calcareous. By calcerous I mean hard as bone china. Examples of these hard operculae, some of which are used in jewelry or as ornaments, can be found in the marine families Naticidae, Trochidae and Turbinidae. Some land snails with operculae include the families Helicinidae, Cyclophoridae, Pomatiasidae and Chondropomatidae.

References
en.wikipedia.org/wiki/Epiphragm
en.wikipedia.org/wiki/Operculum
Note : These comments are generalizations, there are some exceptions ! I covered a lot of unknown ground in preparing this post and would welcome any suggestions and/or amendments

[brunni]

I've searched the forum for comments on aestivation and there are none, apart from Kevin's note on P. H. Nesbet's observations of 1974. An Achatina or Limi ( for example ) would normally be dormant for 4 – 8 weeks a year in it's natural habitat. I would have thought that GAL owners would have posted a host of comments about their pets going in to ( or coming out of ) hibernation.

I conclude that GALS in captivity have such a perfect life ( food, moisture and heat ) that they no longer get triggered to aestivate. Is this assumption correct ?

Do snails need to burrow not only to escape from their conditions but also to develop properly? Should we leave them undisturbed for longer times there ?

[coyote]

I too have wondered about how much the different conditions of pet snails change some of their usual dormancy patterns. I'm sure the tank conditions influence those patterns to one degree or another, but I'm not sure how crucial it is to allow a dormant period now and then for the overall well-being of the snail.

Some say that a snail that doesn't estivate will live a shorter life and they are programmed to do it anyway, others say their snails never go dormant and live long, happy lives, so it is hard to say.

[brunni]

The report of R.H. Nisbet suggests aestivation promotes shell growth.

"One A. (Achatina) achatina received in July 1955, spent only 6 weeks of the following 20 months above ground. Yet, during this period it had increased its shell length by 8.2 mm (120.5-128.7mm) and its breadth by 5.0 mm (65.0-70.0 mm). The addition of new shell to the body whorl at its greatest width was 28.5mm. Most of this additional shell growth occurred while the snail was below ground."

petsnails.proboards.com/index.cgi?board=behavior&action=display&thread=1493

But I guess there's not much fun in having a pet snail thats always sleeping underground.

[ness]

Oooh now that's interesting. I've heard several people call their Tigers lazy, though I suspect that does not apply to all. I would say that mine were fairly average in activity. It makes sense though to grow while resting as all of the energy can go into growth instead of producing slime to move around.

[coyote]

Oct 25, 2011 9:36:33 GMT brunni said:

But I guess there's not much fun in having a pet snail thats always sleeping underground.

True! When I got my Cantareus apertus, I hardly ever saw her because she buried herself in the substrate so much I began to fear I'd forget what she looked like.

[brunni]

R. H. Nisbet was able to observe an A. panthera forming its epiphragm.

„The animal retracts within its shell, leaving about 2-5 mm of the internal surface of the lip exposed. The collar is extended to enclose the retracted foot and secretes a yellowish mucous layer. The latter slowly whitens, finally becoming a thin, tough, shiny and slightly flexible structure with a fine slit that follows the line of the pneumostome.“

He made a drawing which is reproduced below. Note the slit-like opening ( lower left of center ) to admit air. It is positioned directly above the respiratory opening ( called the pneumostome ).

This is in contrast to a Limicolaria`s epiphragm which is rigid, thickened and without any opening.

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[shustrik]

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[shustrik]

brunni,
Can you show a photo of your new limas?[/quote]

[brunni]

shustrik : I'm still trying to work out what species the limis are before posting a pic. Also note I only got shells, not live animals.

Meantime working earlier on the thread "Species Pictures for Website" I noticed on 20 Feb 2006 Kevin Davies posted images his Archachatina ventricosa. One of his images showed a snail in aestivation with the membrane-like epiphragm sealing the aperture, exactly as illustrated in my earlier post. Thanks to Kevin for his image which is posted here.



Anybody else got pictures of GALS in hibernation ?