Some time ago, someone asked whether Cypraea secreted acid.  James comes
to mind as the person.  I said I would ask E. Alison Kay, which I did.
The answer from Alison follows.  Perhaps someone has something to add to
this to round out the subject.

"I finally tracked down the article on acid secretion in cowries. There
was an argument in the early 60's as to whether acid was secreted by
some cowries. I was at the meeting when it was proposed and saw the guy
who presented the data be demolished by a very well known specialist in
molluscan anatomy. However, in 1969 Tom Thompson did publish a paper on
acid secretion in Pacific Ocean Gastropods. Australian Journal of
Zoology 1969 17: 755-764. In summary:

Kniffen, 1968 showed that in laboratory tests Cypraea cervus and C.
zebra secrete acid more or less continuously.  In his 1969 paper
Thompson found acid secretion in Cypraea macula, erosa, annulus,
errones, caurica, vitellus, subviridis, caputserpentis, oryza,
clandestina, moneta, tigris and spadicea. He concluded that the acid
secreted is predominantly sulphuric acid, it is not secreted
continuously as Kniffen said, and the secretion is probably defensive.
I don't know of any later work offhand, but one could have a look
throuigh Zoological Records to see if anything has since been looked at.
                Sorry this took a bit of time. Alison






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