updated Oct 2016
learn only 3 things about them ...
Many anthozoans are small and easily overlooked. Don't
step on it.
Most anthozoans have stingers. Don't touch them!
are important to the habitat. Don't kill or remove them.
seen? Almost all cnidarians we commonly encounter on our
shores are Anthozoans. They are among the most obvious creatures in
coral reefs (hard corals being a member of this group), and come in
a wide range of colours, textures and shapes. Some may be small and
well camouflaged, or well hidden.
are Anthozoans? Anthozoans belong to Phylum
Cnidaria. There are about 6,000 known species of anthozoans, making
them the largest group of cnidarians. About two-thirds of all known
cnidarian species belong to this class.
What are NOT Anthozoans? Commonly
encountered animals that do NOT belong to this group include jellyfishes
Features: 'Anthozoa' means 'flower
animals' in Greek. Some of the more familiar Anthozoans do indeed
resemble flowers. In colonial Anthozoans, the tiny polyps are also
flower-like. For example, polyps of hard corals, soft corals and gorgonians.
Some Anthozoans are not quite flower-like: peacock anemones and sea
The Class Anthozoa is divided into two main groups by the number of
tentacles and internal body structures they have.
Subclass Zoantharia (Hexacorallia) have tentacles which are
generally unbranched and in multiples of six. There are about 4,000
known species of this subclass, the majority of which are hard corals.
Members of the subclass include
Subclass Alcyonaria (Octocorallia) have tentacles which are
branched and in multiples of eight. There are about 2,000 known species
of this subclass.
Flower Power: The flower-like
polyp is the basic structure of all anthozoans. The polyp comprises
a tube-like body column. One end of the tube has the mouth in the
centre (and is thus called the oral disk), usually ringed with tentacles.
In solitary (non-colonial) polyps, the other end of the tube may be
specialised into a flattened foot that sticks to a surface (called
the pedal disk), or is a bulb-like shape that helps to burrow (called
In most Anthozoans, the body column can retract towards the base to
hide from predators or exposure at low tide. At the same time, most
can also tuck their tentacles and oral disk into the body column.
This is usually done by expelling fluids so that the tentacles and
body deflate like balloons. To inflate again, Anthozoans have special
body structures to pump in and retain water.
Many Anthozoans are colonial. A colony is made up of tiny individual
polyps that are connected to one another by tiny canals.
What do they eat? Most Anthozoans
are carnivores. Prey is captured with mucus or stingers (more about
these stingers see cnidarians in general).
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.
Many Anthozoans also harbour symbiotic single-celled algae (called
zooxanthallae) in their tentacles. The algae undergo photosynthesis
to produce food from sunlight. The food produced is shared with the
Anthozoan, which in return provides the algae with shelter and minerals.
It is the zooxanthallae often adds colour to the Anthozoan.
Anthozoan babies: Unlike other
Cnidarian classes, Anthozoans do not undergo a medusa-stage in their
reproduction cycle. The polyp is involved in both sexual and asexual
reproduction. In asexual reproduction, the parent polyp may divide
into two; or portions of the parent polyp (e.g., the foot) may break
away and new polyps develop from the fragments; or the parent polyp
may bud off new polyps.
Status and threats: Many Anthozoans
are listed among the threatened animals of Singapore. For more details
see cnidarians in general.
Eight branched tentacles of a blue
Pulau Semakau, Mar 05
Eight branched tentacles of a sea
Beting Bronok, Aug 05
Eight branched tentacles of a sea
Changi, Jun 05
- 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.