Swimming molluscs : how about this -
 
Okutani, T. (1961) : 'Description of Solariella nektonica, sp. nov., with
special reference to its swimming behaviour'. Venus, vol. 21 (3) : 350-352,
figs. 1-8.
 
The article includes line drawings of the little darling floundering about.
 
(Utterly off-topic, I know, but can anyone tell me whether non-aquatic
birds suchs as sparrows, wrens and so on can swim and take off from water
if they have to? I can think of a simple experiment to confirm this, but
the budgie's owner won't allow it)
 
PC.