[Taxacom] Are slugs subgroup(s) of snails

[Kenneth Kinman]

Dear All,
      Francisco wrote that Tandonia are slugs, not snails.  I guess this
depends on how one defines a snail.  If it must have a shell to be a
snail, then I guess this is true.   However, the word snail seems to
originate from the German Schnecke, which can mean either snails sensu
stricto (shelled forms only) or sensu lato (snails and slugs), depending
on the user.
       The specific German word for a slug is Nacktschnecke, literally
meaning "naked snail".  Therefore, this indicates that at least some
Germans must have regarded naked snails (slugs) as a subset of snails.
Maybe this is a good thing, as it would clearly indicate their
relationship, especially to those who might think slugs are some kind of
worm.  
     That slugs are a polyphyletic grouping doesn't make me particularly
fond of the term either.  So in that sense it is a bit like the term
"worm" (formerly "Vermes"), and we are now more specific when we refer
to particular types of worms (annelids, platyhelminths, nemertines,
nematodes,  chaetognaths, etc.).  So is the term "slug" (another
polyphyletic group) useful enough to insist that it must be used in
place of the more specific phrase "naked snail" (German
"Nacktschnecke")?  Specifically, was Dan actually wrong in calling
Tandonia "snails".  Again, it seems to depend on the usage (sensu
stricto or sensu lato).    
         ---------Cheers,
                        Ken Kinman