> Class Anthozoa > Subclass Zoantharia/Hexacorallia
> Order Actiniaria
learn only 3 things about them ...
| A sea anemone is an animal and not a plant. Don't step
Some sea anemones can sting. Don't touch them.
anemones can be found in all kinds of places. Look for
seen? A wide variety of sea anemones can be seen on all
our shores. Tiny sea anemones often wedge in crevices on rocky shores.
Sandy shores teem with sea 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 sea anemones are
also common in coral rubble areas. Sea 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. Sea anemones belong to the Class
Anthozoa that includes Peacock anemones and hard corals. There
are about 1,350 known species of sea anemones. They are found from
deep to shallow waters, attached to hard surfaces or burrowing into
Features: Most 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, sea anemones are larger solitary polyps that don't produce
a hard skeleton. Like jellyfish and other cnidarians, sea anemones
have tentacles with stingers. What we first notice of the sea 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. Sea 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 sea 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 sea anemones don't move around a lot. Sea 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 sea 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.
Sea anemones that burrow into the ground may have
a bulbous tip at the end of the body column instead. This helps them burrow and stay anchored. Part or most of the body column may be buried or hidden. In sand,
mud or crevices in rocks or coral rubble. The body column may have
bumps or spots (called verrucae). In some, these are sticky. These
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 sea 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, sea 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 sea anemone attempting to swallow a sea pen!
Changi, Jul 04
|What do they eat? Sea anemones
may also use their tentacles or mucus to trap small particles, detritus
and plankton from the water.
But large ones especially, can capture and swallow prey such as fishes
whole. Sea 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 sea anemone lacks an anus. So it has to
spit out any indigestible bits through the mouth.
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
Farm in their arms: Many sea 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 sea anemone, which
in return provides the algae with shelter and minerals. The zooxanthellae
are believed to give sea 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 sea anemones. The Anemonefish (Amphiprion sp.) is coated with mucus that does not trigger
off the host sea anemone's stingers. Other creatures that also make
their homes in sea anemones include anemone
shrimps (Periclimenes sp.).
Babies: Most sea 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 sea 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 sea anemones. The Swimming anemone can regenerate a new anemone from a dropped tentacle.
But not all sea anemones do this, so please don't mutilate sea 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
sea 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.