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Post by muddydragon on Sept 25, 2010 17:02:49 GMT
actually... i've just been looking at my albino snails and photos of previous albino snails i owned i.e. not the leucistic margies. and i can't spot eyespots just everso slightly darker cream areas on the overall darker cream 'eyeball' i think i was confusing them with axoltls because thinking about it snails dont have red blood! they use haemocyanin (well most do) so i would immagine the eyes are there just without any dark pigment, if snails were red blooded the eyespots would be pink, but in this case they should be a pale blue/green which combined with the depth and creamy surrondings probably renders them invisable. it's interesting well spotted ladyescargoth! anyone got any albino fulica with eyespots? (albino and leucistic margies can be easily confused, the main way to tell them apart usually is ones with dark eye spots are leucistic so wouldn't make good examples, to my knowledge there are no leucistic fulica but i could be wrong). alternitavely it is possible that all albino snails are blind due to the visual pigments also being affected.
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Post by ness on Sept 26, 2010 10:31:31 GMT
As I understand it though snails eyesight is so poor that they don't see any colour or detail, but can only detect that there's some light or dark, i.e. the general light level of the area. Does pigmentation (or lack of) actually have any affect on the amount of light an eye can process?
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Post by muddydragon on Sept 26, 2010 12:21:56 GMT
well visual pigments are used in vision, and they do various breaking down when exposed to light it can get complicated fast (in mammals, i assume similarity in molluscs but eyes have evolved many times over) however these visual pigments are not a type of melenin (the one that if missing causes albinoism) in mammals the pupil appears black because it is essentially a 'hole' (filled with transparent goop) light isn't reflected back out so it appears black. some animals have a tapetum lucidum which reflect light back out of the eye, such as when you shine a torch in a cats eyes (not on purpose obviously!). if you disect a cows eye, pop out the lens and anything else you can flip it inside out over your thumb, then it's a really pretty green/blue irridescent colour (due to having a tapetum lucidum) however if you just look at the eye in daylight it apears black. however that's not going on with snails you can see the black spot move when they extend their eyestalks so its not a physical 'its dark in there' black but presumably actual pigment of some sort, it's role however i am unsure of. it's fascinating really i'm sure there must be some papers on it somewhere
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Post by ness on Sept 26, 2010 13:18:08 GMT
Interestingly it's been reported that in albino humans their eyes reflect in a superficially similar way to those of cats, which to quote one albino girl's account "is pretty cool in discos", though we don't have a tapetum lucidum, so the mechanism of that reflective quality must be different... So something else must be going on there in albino humans, and possibly other albino mammals, though I'm not sure what it is. Perhaps albino humans lack certain cone receptors that absorb different coloured light and so some light is relected back? I don't know what it is. I'm making a wild guess. Yes like you say a snail's black eye dot doesn't appear to be caused by a hole. Hmmm (rubs chin and ponders)
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Post by Lady Escargoth on Sept 27, 2010 12:43:12 GMT
Nope, I'm not sure at all about melanin being present in their shells, I thought it was the only pigment responsible for colours in the body.
It might very well not be melanin that colours their shells ! Whet I meant was that I thought them capable of producing some sort of colour since their shells where not yellowish..
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