Slimy!

I always know where my bubble shell snails are; all I have to do is look for the trail of slime bubbles and follow it.

Bubble shell, Haminoea japonica, and Nassa snail, at water surface.

Bubble shells wear their shells inside the body; not much use for protection. Instead, they produce a prodigious amount of mucus and often shelter inside a circle of the stuff. When they leave, it remains stuck to the surface, sometimes on the glass of the aquarium, sometimes rolled into a blob of sand.

The rest of the slug and snail tribes, from our garden slugs to nudibranchs and limpets, are slimy beasts, too, if not as productive.

In snails and sea slugs (nudibranchs), each species has a unique chemical composition to their slime, and within each species, individuals can even be identified. (Ucluelet Aquarium)

This slime is useful stuff. On land, or underwater on scratchy rocks and sand, it serves as a lubricant for the tender foot as it slides along. For going up vertical walls, and sleeping on the underside of a rock, it's a glue.

But that's not all it's good for.

• It's a road map. A snail can follow her own trail home at the end of the day's hunt. Or another may follow her trail, hoping to mate when he catches up with her. I see the Nassa snails doing this often, on the wall of the tank.

• Or a carnivorous snail (or a worm) can follow the slime trail of his prey.

• The slime coating keeps an intertidal critter moist at low tide, when he is exposed to the air.

• It serves as a defense. Some nudibranchs, some sea stars, and other critters exude a thick layer of slime, really sticky slime, when they are disturbed or threatened.

• It may protect the skin against bacteria and parasites.

• And don't forget reproduction! Remember the leopard slugs, that hang from branches on two threads of their own slime to mate in the air? (Video) Other snails transport sperm in a mucus environment, if not as dramatically. And then the moon snail uses her slime to glue sand grains together to build her big "sand collar" egg case.

Bubble shell slime trail on aquarium wall

And I've discovered another function of the slimy goop. When a bubble shell is knocked off his blade of eelgrass, or off his spot on my tank wall, he rappels down to the sand on his slime rope, landing gently at the bottom. Helpful, when your shell is so fragile.

And a couple of days ago, a hermit crab knocked a zebra leafslug off the top leaf of the seaweed. As I watched, the slug floated across to the far side of the tank on a thread of slime, rather like a ballooning spider on her silk.

Handy stuff, that slime!