> Class Anthozoa > Subclass Zoantharia/Hexacorallia
> Order Actiniaria
learn only 3 things about them ...
| An anemone is an animal and not a plant. Don't step
Some anemones can sting. Don't touch them.
Anemones can be found in all kinds of places. Look for
seen? A wide variety of anemones can be seen on all
our shores. Tiny anemones often wedge in crevices on rocky shores.
Sandy shores teem with anemones; some small and well camouflaged
or hidden in the sand. Seagrass meadows often have carpet anemones
that may be bigger than your face! Large colourful anemones are
also common in coral rubble areas. Anemones may also settle on
shells occupied by hermit crabs or even living snails.
What are sea anemones? Sea anemones
are to Phylum Cnidaria, which includes
jellyfishes and corals. Anemones belong to the Class
Anthozoa that includes cerianthids and hard corals. There
are about 1,350 known species of anemones. They are found from
deep to shallow waters, attached to hard surfaces or burrowing into
Features: Most anemones are small, from 1.5-10cm long and 1-5cm in diameter. But
some can be 50cm in diameter or more! Unlike hard corals which are
colonies of small polyps connected to one another that produce a hard
skeleton, anemones are larger solitary polyps that don't produce
a hard skeleton. Like jellyfish and other cnidarians, anemones
have tentacles with stingers. What we first notice of the anemone
is a broad, flat disk. This is called the oral disk because that is
where the mouth is, at the centre of disk. The mouth is usually a
slit. Anemones don't have teeth.
Stingers! The upper side of the oral disk is usually covered with lots of hollow
tentacles. The tentacles are armed with stingers that are used for
feeding and self-defence. Many anemones have
nematocysts or stingers that can inject toxins. They may also have
a kind of stinger that produces a long adhesive thread (called spirocysts).
These make the tentacles sticky and are used to entangle hard-bodied
prey such as crabs that may blunder into them. Stingers are concentrated
on the tentacles.
|Getting a grip: Most anemones don't move around a lot. Anemones also have a long smooth body column. The other end of
the body column may end in a flat muscular pedal disk that attaches
to a hard surface. Some anemones can move slowly by gliding
on the pedal disk. The Swimming anemone can indeed swim, but can also cling in place with its pedal disk.
Many anemones burrow in sand,
mud or crevices in rocks or coral rubble. These may have
a bulbous tip at the end of the body column that helps them dig down and stay anchored. Part or most of the body column may be buried or hidden. The body column may have
bumps or spots (called verrucae). In some, these are sticky, to
help the animal grip the surroundings where it is buried, or to keep
the oral disk spread out, flat against a hard surface.
In most anemones, the body column can retract towards the base
to hide from predators or minimise exposure at low tide. Most can
also tuck their tentacles and oral disk into the body column. When
small anemones do this, they look like beads of jelly. Others can
simply retract their entire bodies into a hole, crevice or into the
sand. This is usually done by expelling fluids so that the tentacles
and body deflate like balloons. To inflate again, anemones have
special body structures to pump in and retain water.
Long body column of a burrowing Snaky anemone.
Beting Bronok, Aug 05
The Swimming anemone really
Pulau Sekudu, Jun 06
Some anemones are tiny and lie
half buried in the sand. Don't step on them!
Chek Jawa, Oct 04
Carpet anemone eating a sand dollar
Chek Jawa, Feb 04
A tiger anemone attempting to swallow a sea pen!
Changi, Jul 04
|What do they eat? Anemones
may use their tentacles or mucus to trap small particles, detritus
and plankton from the water. Larger anemones can capture and swallow prey such as fishes
whole. Anemones have stingers like other
cnidarians. Prey is captured and immobilised with these stingers.
Tentacles may push larger prey into the central mouth. The edges of
the mouth may be inflated into 'lips' that pucker to hold prey as
it is swallowed. The mouth and body column can expand wide to accommodate
the prey whole. Or the anemone may fold its oral disk over the prey.
Like other cnidarians, the anemone lacks an anus. So it has to
spit out any indigestible bits through the mouth.
Farm in their arms: Many anemones
also harbour symbiotic single-celled algae (called zooxanthellae)
in their tentacles. The algae undergo photosynthesis to produce food
from sunlight. The food produced is shared with the anemone, which
in return provides the algae with shelter and minerals. The zooxanthellae
are believed to give anemone tentacles their brown or greenish
Anemone friends: Some anemones
may live with other animals such as hermit
crabs and living snails. Other animals
have adapted to live among the tentacles of anemones. The Anemonefish (Amphiprion sp.) is coated with mucus that does not trigger
off the host anemone's stingers. Other creatures that also make
their homes in anemones include anemone
shrimps (Periclimenes sp.).
Should I 'save' animals trapped in an anemone? Please don't. If you do, you will be depriving the anemone of a meal.
It might not get so lucky again for a while. The animal that you 'saved'
might also not survive if it was badly stung by the anemone.
Should I feed the anemones? Please
don't. Anemones know how to feed themselves. You might hurt the anemone
if you put the wrong thing on it, for example a toxic animal. If you
put another living animal on an anemone you will be hurting two animals.
Please don't put objects such as litter or dead crabs on an anemone
Babies: Most anemones are hermaphrodites,
but act as one gender at any one time. That is, they produce either
sperm or eggs during one reproductive period. Fertilisation may be
external, or the eggs may be fertilised inside the anemone. The eggs
develop into free-swimming larvae that eventually settle to the bottom
and develop tentacles.
Some anemones can reproduce asexually by detaching a portion of
their body, such as the pedal disk, or even by dividing into two.
The detached portion eventually grows into new anemones. The Swimming anemone can regenerate a new anemone from a dropped tentacle.
But not all anemones do this, so please don't mutilate anemones.
Human Uses: Unfortunately, these
beautiful creatures are popular in the live aquarium trade and many
are harvested from the wild for this trade. Studies of their fascinating
structures have medical applications, such as the use of their stingers
substances through human skin.
Status and threats: None of our
anemones are listed among the endangered animals of Singapore.
However, like other animals harvested for the live aquarium trade,
most die before they can reach the retailers. Without professional
care, most die soon after they are sold. Those that do survive are
unlikely to breed successfully. Like other creatures of the intertidal
zone, they are affected by human activities such as reclamation and
pollution. Trampling by careless visitors, and over-collection also
have an impact on local populations.
Actiniaria recorded for Singapore
text index and photo
index of sea anemones seen on Singapore shores
- D. G. Fautin, R. Tan, N. W. L. Yap, Tan S. H., A. Crowther, R. Goodwill, K. Sanpanich & Tay Y. C. Sea anemones (Cnidaria: Actiniaria) of Singapore: shallow water species known also from the Indian subcontinent. 10 July 2015 The Comprehensive Marine Biodiversity Survey: Johor Straits International Workshop (2012) The Raffles Bulletin of Zoology 2015 Supplement No. 31, Pp. 44-59.
- Daphne Gail Fautin, S. H. Tan and Ria Tan. Dec 2009. Sea anemones
(Cnidaria: Actiniaria) of Singapore: abundant and well-known shallow-water
species. The Raffles Bulletin of Zoology. Pp. 121-143.
- 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.
- Wee Y.C.
and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
National Council on the Environment. 163pp.
- Ng, P. K.
L. & Y. C. Wee, 1994. The
Singapore Red Data Book: Threatened Plants and Animals of Singapore.
The Nature Society (Singapore), Singapore. 343 pp.