Paul
I am extremely impressed if Talia understood your joke, I am not trying it on my 8 year old grandson! I'm sure he's never heard of HMS Nautilus (his great grandfather worked for a company that built nuclear subs!) but he just might be aware of the mollusc.
But, ho ho, If you believe Santa can get down chimneys when he is somewhat overweight, why not underwater?
Best wishes for the New Year