MadSci Network: Zoology
Query:

Re: why do barnacles cling to the side of a rock?

Date: Mon Nov 13 21:40:41 2000
Posted By: Alastair Lyon, Science Information Officer
Area of science: Zoology
ID: 974088205.Zo
Message:

They're actually called limpets. The small, almost star shaped animals 
stuck VERY tightly to rocks at low tide.

Limpets are molluscs (ie. sea snails) that have a small shell "hat", 
rather than the traditional coiled shell like the common garden snail has.
Limpets move around at high tide and slowly graze on the algae on their 
rocks. At low tide, they have proven homing instincts and always return to 
their "home scar", where their shell fits into the rock EXACTLY.

Barnacles are similar in description, but they have a cemented carapace 
(ie. house) that a small filter feeding arm pokes out of in the middle. 
Barnacles are modified crustaceans (same family as crabs, lobsters etc.) 
and the little arm that sticks out is called a "cirri". Barnalces are 
immobile - they feed on planktonic life drifting past. They settle from 
the plankton onto rocks using specialised homing cues and actively seek 
out adult barncles while they are in the free swimming planktonic stage. 
Once they're happy, they settle on a chosen piece of rock and begin to 
change into an adult barnacle. Sometimes even whales are considered a good 
home for a colony of barnacles!
You can easily see barnacles on the pier pilings on a wharf - lean over 
and have a good look at low tide.

Hope this helps!

-Alastair


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