Friday, May 4, 2007

Limpets: Snails with Hats

Three NAKED Facts

Interactive activity: I see (insert number) animals on this rock. Can you find them?

Thoughtful question: What do you think these animals are? Crabs? Snails? Bugs?

NF#1: A limpet is a snail with a hat! Like other snails, it has a very broad foot. Instead of a coiling snail shell, it has a hat-shaped shell. To protect itself (from water loss and animals that try to eat it), a limpet uses its broad foot to clamp its hat-shaped shell firmly to the rock. It clings so tightly that you will hurt it if you try to pry it off the rock. So please don't do that.

If they want to see what the limpet looks like under its hat, there's a large photo of this in the Chek Jawa guidebook, pg. 55.

Corny joke: A limpet has a permanent umbrella!

NF#2: Limpets can move. At high tide, they munch on tiny plants that grow on the rocks (algae). The rock surface around a bunch of limpets is usually clear of algae and other animals (like barnacles and oysters).

NF#3: Home on the Rock. When the tide falls and things get dry, some kinds of limpets go back to the same spot, called the 'home scar'. The limpet rubs its shell against the rock on this same spot, wearing away the shell and/or the rock so that a perfect fit is created! Even as the limpet grows bigger!

Sometimes, you might come across a spot on a rock in the shape of a limpet that is completely 'clean' and free of growths. This could be the home scar of a limpet that has recently come to an unhappy end. In the photo above, you can see the feeding trails leading from the home scar.

Some limpets are believed to follow their mucus trails back to the home scar. In some of these homing limpets, their mucus also stimulates the growth of algae!

Too Much Information
Too much limpet info can make ordinary people go limp. Beware!

Two major groups of snails have umbrella-shaped shell. They come from separate groups and are not closely related.

True Limpets
One group of snails with hats called True limpets breathe through gills. Some have holes at the top of their shells, others don't.

Star limpet (Patelloida sacchroides) Family Lottidae
This is a True limpet that breathes through feathery gills. About 4cm, common, usually found on large boulders.

Smooth limpet (Cellana sp.) Family Nacellidae
A True limpet, it breathes through a ring of gill leaflets. 2-3cm, uncommon, usually in shady places near the mid-water mark.

Keyhole limpet (Diodora sp.?) Family Fissurellidae
This is a True limpet that has a hole at the top of the shell. About 1cm, usually found under stones near the low water mark. Water is sucked in from under the shell, passes over the two feathery gills, and is then expelled out of the hole in the shell. Because of this hole, these limpets must live in wetter places.

False limpets

Another group of snails with hats have lungs and breathe air. False limpets (Family Siphonariidae) belong to this group and are closely related to land snails and to onch slugs (Family Onchididae). Because they can breathe air, false limpets are often found higher up on the rocks than limpets that breathe through gills.

Guam false limpets (Siphonaria guamensis) Family Siphonariidae
About 1-2cm, common and usually found on hard surfaces near the high water mark.

Javan false limpet (Siphonaria javanica) Family Siphonariidae
About 1-2cm, common and usually found near the high water mark.

Large false limpets (Siphonaria atra) Family Siphonariidae
About 2-3cm, usually found on large boulders near the mid-water mark. Not commonly encountered.

No comments: