Ok well the more I read the more confused I'm getting. There doesn't seem to be any definitive descriptions that I can find to help me know the difference, and in photos of things that are opaline/opalino/alabastro, the terms seem to be interchanged, sometimes referring to identical items.
Like this one which is listed as both alabastro and opalino: http://www.rubylane.com/shops/murano-glass/item/107
But it looks like it irridesces to me, and then when I tried to find a defnition of opalino I found stuff that said it had flecks of crystaline stuff in it that made it react to light like an opal. They also have this one: http://www.rubylane.com/shops/eyesnglas/item/2265
but again the colour seems to change on different angles and my snail stays the same colour no matter what angle you're looking at the glass. That was why I thought maybe it's not opalino.
So then I stumbled across alabastro in my searches, and it seems to fit a bit better (to my completely novice eye): http://antiquehelper.rfcsystems.com/Full/224/56224.jpghttp://www.20thcenturyglass.com/images/items/murano_glass/archimedeseguso_glass/segusoglass_mexicans01.jpg
(these are labeled 'mexicans' for some reason. they don't look Mexican to me..)
On this chart though, the alabastro ones (pale white, light rose, and medium rose) seem more like my snail than the opalino examples:http://www.beadfx.com/catalogue/glasschart.html
On my snail you can see the light passing through it, as if you were looking at it through slightly watered down milk, or really smooth fine wax. The thin edges of the snail's body and it's little 'horns' are a bit more seethrough but still cloudy.
Anyway, thanks for your help everyone - I guess I'll never know unless I find an expert here in New Zealand who can look at it in real life, and it's not that big of a deal Moderator: Linked images changed from display to links