Flora & Fauna: Slugs

eggshaped · 327854. Wed Apr 30, 2008 9:19 am

Question: What do you call a slug with a shell?

Forfeit: A snail

Answer: A shelled slug

Notes:
Scientifically, the word snail is a common name for all members of the class of molluscs called “gastropoda”, but most commonly it is used for members of that class who live on land and have a hard shell. Slug, however, is used to describe gastropods who are taxonomically indistinct from snails, but have no shell. Between snails with shells and slugs without, there are numerous different grades of shell reduction including internal shells and comically tiny shells that have no longer any real purpose. These slugs with vestigial shells are known as half-slugs or shelled slugs, they belong to the family Testacella.

Testacellids are quite hard to find, they live underground and search for their favourite food, earthworms, with their acute sense of smell. They hold their prey with their dagger-like teeth and swallow it alive and whole.

The general evolution of shell reduction is known as Vitrinization, after the Vitrinidae family of glass snails, a group who occupy a more central space between snails and slugs and get their name for their smallish translucent shell.

Snails get along with slugs, even allowing the occasional piggy-back ride on their shells. Many slugs are hermaphroditic, they mate reciprocally, with both slugs inserting their penis into the partner at the same time. Before mating, slugs leave chemicals in their slime to tell others they are ready, slug foreplay consists of eating each others slime, after mating, slugs will sometimes chew the penis completely off of their partner. This is called apophallation.

Additional sources:
http://www.weichtiere.at/english/gastropoda/terrestrial/testacella.html
http://www.weichtiere.at/english/gastropoda/terrestrial/vitrinidae.html
Slug research from Animal Ig book

Picture Ideas:
As one of the worst questions we've ever had on the show, this will only work, I feel, if we have a picture of a slug with a ludicrously small shell.

Here's one:

here's another:

WB · 327920. Wed Apr 30, 2008 11:29 am

Could not another forfeit be A Bullet or something?

Is there a way of slanting the question a bit to open it up in this way? (desperately trying to help make it more interesting........)

Tim Barnes · 816921. Tue May 17, 2011 9:20 am

is there a name for the group of animals that have shells, or homes on their backs?

CB27 · 816947. Tue May 17, 2011 11:30 am

Any invertebrate with an exoskeleton is called an Arthropod.

I'm not sure if there's a collective term for reptiles, mammals and other groups which have an exoskeleton, it might be that their group is not big enough to warrant one.