Hello Helmut,
 
I believe the name "dog" in reference to a shell is an Old English
expression meaning commonplace or ordinary.  In the case of Strombus
canarium of course, the scientific name specifically refers to dog
(canarium = canine), hence the common name "dog conch".  However,
there are other species where the common name "dog" is used, even
though the scientific name doesn't mean dog, such as Nucella lapillus
(dogwinkle) and Glycymeris glycymeris (dog cockle).  The scientific
name vulgaris (or vulgare) - "vulgar" is similar in meaning -
commonplace, ordinary, nothing special.
 
Paul M.