Why do they call it an Oyster Card?

From Wikipedia:

Oyster was conceived and subsequently promoted because of the metaphorical implications of security and value in the component meanings of the hard bivalve shell and the concealed pearl. Its associations with London through Thames estuary oyster beds and the popular idiom 'the world is your oyster' were also significant factors in its selection as was the uniqueness of the word Oyster.

Well as I understand it the name was selected because an oyster is protected with a hard shell (technical security) and has a pearl inside (transit mobility). Also the oyster beds of the Thames were famous from antiquity so it's very "London". On the other hand it could have been thought up after to many pints!

I thought it had to do with the curious oysters from Alice in Wonderland.

Thanks.

When my Grandmother asked, I told her maybe it was a take off on the phrase, i.e. With the card, London is your Oyster, but that seemed so cliche. I tried to explain that you have to touch the card to a reader, and maybe someone decided that was shaped like an Oyster, but really it was conjecture and I had no idea. I guess if nothing else, the name has at least generated conversations about transit that just don't seem to occur when discussing bus tickets or subway passes.

As for the after 11 crowd, of which I am often a member here on the West Coast. Here is the crazy thought from last night. Part of the reason the dollar has fallen so much is investors pulling their funds from dollars and putting it into oil, hence oils rise. Lets make a concerted effort to take some of the glory from oil, start an effort for people to go car free for Memorial Day weekend. If oil goes down and the dollar goes up, we will make our European trips cheaper over a three day weekend.

And here I thought it was so named because you have to have a lot of "clams" to be able to afford to visit London these days.

Is the exchange rate for clams any better than that of the dollar? If so, I will stock up on clams in my carry on and trade when I get there.

I went to the website for the Oyster Card: www.tfl.gov.uk; there was no hint as to why it is called "Oyster." I've used the card; it's convenient and saves time and money. I was able to use it on the bus near Heathrow, so apparently its usefulness extends beyonds the bounds of London. What makes it so easy to use is that you leave the plastic hard card within its bright blue cover and pass the whole thing over the yellow reader when entering and leaving the Tube. On buses you pass it over the reader only on entering the bus. On exiting Tube stations a monitor gives you the amount left on the card so you know when to "top it up."