What is this stuff? A pigment? A protein?
How widespread is this stuff in snails?
Is it found in all of them?
What is it stored in? Specialized cells?
If so, what are they called?
I know that I am looking for details about the epidermis of the mantle.
Does anyone have any Fate Maps for these creatures?
I know that the skin is innervated
http://webs.lander.edu/rsfox/invertebrates/pomacea.html
The many nerves of the cerebral ganglia serve the sensory structures of the head including the skin, labial tentacles, cephalic tentacles, statocysts, and eyes...
The general body surface is also sensitive to chemical and mechanical stimuli...
It also seems that carotenoids might be the pigments, but that seems like a shot in the dark to me at this point.
The most sensitive parts of the snail, as well as the thinnest parts have the largest visible amounts of the pigment, but perhaps it is also found under the shell? I don't know and don't want to take apart a snail to see.
http://en.wikipedia.org/wiki/Carotenoid
Their colour, ranging from pale yellow through bright orange to deep red, is directly linked to their structure. Xanthophylls are often yellow, hence their class name. The double carbon-carbon bonds interact with each other in a process called conjugation, which allows electrons in the molecule to move freely across these areas of the molecule. As the number of double bonds increases, electrons associated with conjugated systems have more room to move, and require less energy to change states. This causes the range of energies of light absorbed by the molecule to decrease. As more frequencies of light are absorbed from the short end of the visible spectrum, the compounds acquire an increasingly red appearance.
And that would explain the color. This type of molecule is often bioactive in many creatures in regards to light, notably it occurs in these snails, and the eggs of the snails are known to have a bad flavor, however what if photo-activity also plays a role in the presence of these pigments in the eggs? They could protect the eggs from harmful solar radiation, for example, and if coupled with a photosynthetic organism, a symbiont, they could provide food for the eggs via photosynthesis, although this seems far fetched. Tridachnid clams however are known to house photosynthetic symbionts in the mantle, but these are obtained by the young clams, which are produced by spawning zygotes into the open ocean, rather than obtaining sperm and producing eggs.
http://www.scielo.org.ar/scielo.php?scr ... 6000200014
In our previous review (Castro-Vazquez et al., 2002) we suggested the existence of a symbiotic association of P. canaliculata to a large prokariont bearing chlorophyll-like pigment/s. The putative symbiotic corpuscles were found in midgut gland and feces of all P. canaliculata individuals from various places, which would indicate an obligate symbiotic association. Similar pigmented corpuscles were also found in the midgut gland and feces of P. insularum and P. scalaris, as well as in Asolene pulchella . Although the search for the presence of putative symbiotic elements in the latter species was not as thorough as that in P. canaliculata , both at the individual and population levels, it was also suggested that they would be obligate symbioses.
So there is a report of at least three Pomacea species having an snail dependent symbiotic organism that has chlorophyll like pigments, while the adult snails are not transparent, the eggs tend to allow some light to pass through and coupled with a carotenoid, a potential for a photosynthetic energy source is plausible, though in need of demonstration. But as far as indications, if this is true, one would expect that light itself as a factor should affect snail development in a positive way, although the snails should not be dependent upon it. In the care section of this website is found the following information:
Light dependent growth has been observed by Pomacea glauca. If the snails were kept in a completely dark environment, their growth decreased, compared with animals that were kept in a 12 hour/day light environment.
This also indicates that more research is needed in regard to these animals pigments and symbiotes.
If I am not mistaken, small snails also tend to be more transparent, allowing the potential for light to penetrate to the gut.
more from the last site
Strong evidence for the bacterial nature of these corpuscles has come from the amplification of a 1500 bp DNA fragment corresponding to the bacterial 16S rRNA gene, using DNA extracted from glandular C and K corpuscles as template (Vega et al., 2005). However, DNA sequence identification of the symbiont, as those recently obtained for the cyanobacterial endocytobionts associated to the diatoms Climacodium frauenfeldianum (Carpenter and Jason, 2000) and Rhopalodia gibba (Prechtl et al., 2004) is still wanting. Nevertheless, both the size and the chlorophyll-like pigment/s of this bacterium strongly suggest that it should be a cyanobacterium in the order Chroococcales or Pleurocapsales.
It should be noted that the Cyanobacteria have been particularly successful in developing symbiotic associations during evolution, involving protists, fungi, plants and animals; however, known cyanobacterial endocytobioses are comparatively rare
So the symbiote is likely a cyanobacteria!
Nothing is known of the functional significance of this mollusk/bacteria endocytobiosis. Even though C corpuscles have chlorophyll-like pigment/s, it should be stressed that they would not be able to perform photosynthesis in the dark environment of the ampullariid midgut gland. Instead, chloroplasts occupying the cells of the many terminal midgut gland tubules located below the slug´s transparent dorsal mantle, are able to photosynthetically reduce carbon, and to transfer photosynthate to their host (Rumpho et al., 2000).
Transmission of the bacterial endocytobiont of P. canaliculata seems to occur vertically, i.e. it is directly transferred from mother to offspring, since pigmented corpuscles appeared in juveniles that were hatched aseptically and that were afterwards cultured in sterile media (Koch et al., 2003)
So when light can reach them, then they may have the potential to reduce carbon?
This may relate to eggs and infant snails ecology.
A single obligate symbiosis (an endocytobiosis) of P. canaliculata with a prokariont has been described (Castro-Vazquez et al., 2002; Koch et al., 2005; Vega et al., 2005). The question of the presumptive cyanobacterial nature of this prokaryotic endocytobiont is interesting, because known cyanobacterial endocytobioses are just a few and, so far, no one has been described in a mollusk (Vega and Castro-Vazquez, in preparation). Also, though several symbioses of mollusks with intracellular chemoautotrophic bacteria have been described (Cavanaugh, 1994; Felbeck, 1987; Shively et al., 1998; Windoffer and Giere, 1997), no symbiosis is known involving the cells of the midgut gland, except for the one presented here and for the already mentioned case of "kleptoplasty".
This just blows me away.
Now what if the pigment I am asking about is a carotenoid?
well according to the wiki on it:
Humans and animals are incapable of synthesizing carotenoids, and must obtain them through their diet, yet they are common and often in ornamental feature
This means that the snail should not code for the carotenoid, but perhaps the endocytobiont does?
The position of the orange pigments on the thinnest parts of the snail is curious.
They are concentrated around the edge of the foot, and when my snails rest they tend to stick this edge or rim outside of their shell, leaving their operculum slightly open, and they sit there and breathe with their gills. I have seem them draw in the mantle and still breathe the same way, but only when frightened.
Even my dark form bridgesii snail has this habit of hanging the edge of it's foot out, and like the other snails it wrinkles the edge, increasing the surface area, and tends to hold it facing light.
I have noticed that when in the shade, the snails tend to rest more closed unless eating, and in the light they tend to rest more open. Perhaps I am mistaken in seeing this, but it also seems that my bridgesii snails are a bit less active when the light is on, and forage more when the light is out.
The more I think about it, the more I want to formulate it as a theory; that photosynthetic symbiosis plays a role in these amazing creatures. The cana is considered a pest in agricultural regions with aquatic conditions, these type of environments are high light areas, hence they are agricultural regions.
In the home aquarium, many keepers of the snails use lights and frequently the eggs are laid in fairly close proximity to the lights. In nature the eggs are typically placed in areas where light reaches them, from what I have seen in numerous photographs.
I am going to predict that sooner or later someone will make the "discovery" that these snails are photosynthetic in one way or another and that supplementing their food with light results in better growth because of this.
I am going to begin designing experiments to see if this can be proven true or false in an obvious and clear manner.
Also I would love the thoughts of other snail lovers here about this topic and or anecdotes of how their snails behave in regard to light.
Thanks!
