learn only 3 things about them ...
They are NOT clams or even snails! They are more similar
to crabs and shrimps!
A living barnacle has a door over the opening in its shell.
A dead one has a gaping hole. Other animals may shelter
in the empty shell.
affect urban living. They grow on ships and thus affect
shipping. Cities rely on ships for supplies and transportation!
seen? Barnacles are often ignored as our attention is drawn
to more colourful and attractive shore animals. But barnacles are
fascinating in their own right! Barnacles will grow on any hard surface
immersed in seawater, so they are found literally everywhere in the
intertidal zone. Barnacles are found on rocks, mangrove trees, pillars,
boats. Barnacles are even found on other animals such as whales
and sea snakes. There are often even barnacles on top of other barnacles!
What are barnacles? Barnacles
are crustaceans like crabs and shrimps.
But they belong to a different group, their own Class Cirripedia.
There are about 900 species of barnacles.
Features: Barnacles are often
mistaken for snails because of their hard 'shells'. However, barnacles
as actually crustaceans. The larvae of barnacles are shrimp-like and
swim freely. As it develops, the larvae eventually glues itself head
down onto a hard surface and develops a conical outer shell-like structure
made up of several plates (wall plates). There is an opening at the
centre of this 'shell'. At low tide, the opening is sealed by a door
(operculum) made up of a pair of plates. A barnacle without these
plates is a dead barnacle! Some barnacles species can be identified
by the shape of the operculum plates and number of wall plates.
Sometimes confused with limpets
which are snails. Here's more on how to tell apart shelled
animals found on rocks.
What do they eat? When the tide
comes in, barnacles open up their plates and extend their feathery,
segmented legs to gather plankton from the water. The legs form a
basket that scoops inwards where mouthparts scrape the edible particles
off the legs and transfer these particles to the mouth. 'Cirripedia'
means 'hairy foot'
Barnacle babies: Barnacles are
usually hermaphrodites, each barnacle having both male and female
reproductive organs. However, they don't self-fertilise. They also
don't release eggs and sperm into the water at the same time, like
many other marine creatures. Instead, they practice internal fertilisation.
As these animals cannot move, this is achieved by having tremendously
long male organs! Some have an organ that can reach another barnacle
7 shells away! A study, however, has found that longer
isn't always better, for a 'male' barnacle.
In some species, a miniature male-only individual settles into the
'shell' of a larger member of its species. Reduced to little more
than a sack of sperm, the male relies on its 'host' for protection
and sometimes even food, in exchange for fertilisation services.
Many barnacles brood their eggs, releasing the free-swimming larvae
that look nothing like the adults. The first form is a nauplius which
looks shrimp-like with antennae, an eye spot, jointed appendages and
a shield-shaped body. The larva spend some time drifting with plankton,
moulting several times.
Eventually, it changes form into a cyprid larva which has a hinged
hardened body with large antennae and more appendages. At this stage,
it does not feed and uses its chemical and touch detectors to detect
adults of its own species and suitable areas for it to settle down.
When it finds the right place, it secretes a glue from special glands
in its antennae to attach itself permanently. Barnacles tend to settle
where others of their own species have already settled. For animated
diagrams of the larval stages of a barnacle, see Keith
Davey's site. Here are fascinating photos
of a barnacle larva on Image
Quest 3-D Marine Library
Barnacle zonation: An ideal spot
for a barnacle is lower down the rock where it gets wet more often.
The further up a rock a barnacle settles, the hardier the barnacle
must be to withstand longer periods out of water and the heat of the
sun. There is competition among barnacle larvae for the best spots
on a rock to settle down on. Each species of barnacle survives best
in a spot where it does better than its competitors. As a result,
different species of barnacles are found in distinct
zones on a rock.
barnacles: Stalked or Goose barnacles are sometimes seen
on our shores. These barnacles have a distinct stalk that connects
the body to the hard surface. Lepas sp.
has white plates and clumps of this species often attached to floating
objections like boats or snail shells. Some barnacles burrow
into living corals, others may be found in
Some barnacles have become parasites that live inside other animals.
Parasitic barnacles such as Thompsonia
sp. grow through the body of the host crab like a root system.
The parasite does not kill the crab but it does affect the crab's
reproductive system such that the crab becomes infertile. The parasitic
barnacle eventually produces egg sacs that emerge through the crab's
Role in the habitat: Despite their
protective plates that are strongly glued down, barnacles are eaten
by crabs, snails such as drills
and the Spiral
melongena snail and other predators. Dead barnacle shells provide
hiding places for many small creatures. Sometimes you might see tiny
mussels, small periwinkles and other animals hiding in the hollow
shell of a dead barnacle.
Human uses: Barnacles are considered a menace to the shipping
industry. An encrustation of barnacles soon develops over every ship
hull. This reduces the speed of the ship and increases fuel consumption.
Efforts to deter barnacle infestation include coating ship hulls with
a toxic paint. However, this does not last and the toxic paint poisons
The barnacles' tendency to accumulate heavy metals in their plates,
however, makes them useful as bio-indicators to measure water pollution.
The strong glue that barnacles use to cement themselves to the rock
has been studied for use in dentistry for a similar protein cement
to fit dentures. The glue has amazing properties: it hardens quickly
under water and continues to work under pressure, in strong acids
or alkalis and temperatures up to 225° C (440° F). The glue is so
strong that even after the barnacle dies, its 'shell' stays stuck
to the rock.
It is a common misconception that barnacles are used to
make the popular local dish of oyster omelette or 'or luak'. The ingredient
in that dish is indeed oysters and NOT barnacles.
Status and threats: Our barnacles are not listed as endangered.
However, like other creatures of the intertidal zone, they are affected
by human activities such as reclamation and pollution. Trampling by
careless visitors also have an impact on local populations.
A variety of barnacles.
Tuas, May 05
Feathery feet of a barnacle.
Woodlands, Jul 08
The large Volcano barnacle has
a honey-combed internal structure
Chek Jawa, Apr 02
A pair of plates form the operculum
that seals the shell opening.
Tuas, May 05
Barnacles on a living snail.
Changi, Jun 05
Like other crustaceans, barnacles also moult!
Is the long structure its penis?!
Seletar, Feb 12
barnacles on Singapore shores
Cirripedia recorded for Singapore
Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity
*from Tan, Leo W. H. & Ng, Peter K. L., 1988. A Guide to Seashore
**from Ng, Peter K. L. & N. Sivasothi, 1999. A Guide to the Mangroves
of Singapore II (Animal Diversity).
***from Lim, S., P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the
Sea: The Life and Times of Labrador Beach.
sp. (Acorn barnacle)
Balanus amaryllis=^Striatobalanus amaryllis
Balanus amphitrite=^Amphibalanus amphitrite
Balanus variegatus=^Amphibalanus variegatus
sp. (Star barnacle)
Chthamalus withersi=^Microeuraphia withersi
Iblidae (Stalked barnacle)
Ibla sibboge=^Ibla cumingi
Lepas sp. (Goose barnacle)
Lepas fascicularis=**Dosima fascicularis
Poecilasmatidae (Tiny stalked barnacle)
sp. (Coral barnacle)
Pyrgoma anglicum=**Megatrema anglicum
sp. (Parasitic barnacle)
***Thompsonia dofleini=^Diplothylacus sinensis
***Thompsonia pilodiae=^Thylacoplethus pilodiae
sp. (Parasitic barnacles)
on crabs (Balanus, Octolasmis), Parasitic
barnacles (Thompsonia, Sacculina) Tan, Leo W. H. &
Ng, Peter K. L., 1988. A
Guide to Seashore Life. The Singapore Science Centre,
Singapore. 160 pp.
Ng, Peter K. L. & N. Sivasothi, 1999. A
Guide to the Mangroves of Singapore II (Animal Diversity).
Singapore Science Centre. 168 pp.
on Australian Seashores by Keith Davey on the Marine Education
Society of Australia website: Fact sheet on barnacles with lots
of animated diagrams of barnacles at all stages of their development
and details on various species of barnacles found in Australia.
On the Rocks by Stephanie Greenman on the Wild California
website: lots of easy-to-read details on the barnacles life cycle
and strange mating habits, including the 'dwarf male'.
Living on the Edge by Wim van Egmond on the Microscopy UK
website: brief introduction with lovely large photos of a feeding
barnacle and the various stages of its life cycle.
Secret Life of Barnacles by Phil Rainbow on the Fathom website:
more detailed but still easy introduction with lots of photos,
including how barnacles can be used as bio-indicators.
penis: longer isn't always better on the wild shores of singapore
of barnacle glue revealed on the wild shores of singapore
- Edward E.
Ruppert, Richard S. Fox, Robert D. Barnes. 2004.Invertebrate
Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963.
Jan A., 2005. Biology
of the Invertebrates.
5th edition. McGraw-Hill Book Co., Singapore. 578 pp.
- Lim, S.,
P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life
and Times of Labrador Beach. Division of Biology, School of
Science, Nanyang Technological University & Department of Zoology,
the National University of Singapore. 160 pp.
Helmut, 2001. Crustacea
Guide of the World: Atlantic Ocean, Indian Ocean, Pacific Ocean
IKAN-Unterwasserachiv, Frankfurt. 321 pp.
- Jones Diana
S. and Gary J. Morgan, 2002. A Field Guide to Crustaceans of
Australian Waters. Reed New Holland. 224 pp.