> Class Anthozoa > Subclass
Zoantharia/Hexacorallia > Order Ceriantharia
learn only 3 things about them ...
They are animals and not plants!
Unlike other anemones, they have two types of tentacles:
long outer tentacles and short inner tentacles.
retract into their tubes at low tide. Don't step on the
seen? These elegant animals with long colourful tentacles
are commonly encountered on many of our shores. They are often seen
in soft, silty muddy areas, as well as in sandy areas near seagrasses.
At low tide during a cool morning or evening, cerianthids in a pool
of water might continue to extend their tentacles. Otherwise, they
are often overlooked because their long, colourful tentacles are retracted
completely into their sand-coloured tubes. Do watch your step to avoid
stepping on them.
What are cerianthids? Cerianthids
are Cnidarians that belong to the
same Class Anthozoa as sea anemones.
There are 50-75 known species of cerianthids in three families. They
come in a wide range of colours and patterns and are thus sometimes
called peacock anemones. However, they are not true anemones, which
belong to Order Actiniaria.
Features: Up to 30cm in diameter
with tentacles expanded, those seen from 5-15cm in diameter. The cerianthid
is a large, solitary polyp that burrows in soft ground and lives permanently
in a tube. So it is also sometimes called the tube anemone or the
The cerianthid has two types of tentacles. An outer ring of long graceful
tentacles called the proximal tentacles. Some species have only one
ring of proximal tentacles, others have several. These long tentacles
gather food from the water. There is an inner ring of shorter tentacles
that ring the central mouth, called the distal tentacles. These short
tentacles tuck food into the mouth.
Cerianthids come in many different colours and patterns, hence their
common name. The short tentacles may be a different colour from the
long tentacles. The long tentacles may be banded or variegated. Sometimes,
cerianthids are encountered with their long tentacles coiled in spirals.
A cerianthid has stingers like other
Cnidarians. A cerianthid makes its tube using specialised stingers
called ptychocysts. Only cerianthids have ptychocysts. These stingers
create adhesive strings that mat together with sand and slime and
hardens to form a tube that has been described as leathery, felt-like
The tube can be more than 1m length in some cerianthids! Only a short
part of the tube sticks out above the ground. The rest is buried in
the ground. Often, at low tide, all you will see of a cerianthid is
a short portion of its soft tube that sticks out of the ground. Please
don't try to dig up a cerianthid. You will hurt it and it may die
if it is not properly anchored and gets washed away with the incoming
The cerianthid doesn't have a 'door' to close the opening of its tube.
To seal the tube and reduce water loss at low tide, the top part of
the tube often flops over, with the animal hidden deeper in the ground.
The cerianthid's body column is long, narrow and smooth. It doesn't
have verrucae like sea anemones. The body column comes in many colours
from white to purple. Being adapted to live in soft sediments, its
body column doesn't end in a flattened pedal disk. Instead, it has
a smooth tip called the physa. This tip can be expanded into a bulbous
shape and is used to burrow with and to anchor itself in the soft
ground. Strong muscles along the length of the body column allows
it to retract completely into its tube in a blink of an eye.
The cerianthid cannot tuck its tentacles into its body column like
sea anemones do. Instead, it bundles its tentacles together and the
entire animal retracts down into the protective tube.
Sometimes confused with sea
anemones. Here's more on how
to tell apart animals with a ring of smooth tentacles.
What do they eat? Cerianthids
do not harbour symbiotic algae (zooxanthellae). They feed on plankton
and suspended food particles which they gather from the water. Cerianthids
have potent stingers that can even be released into the water. These
floating stingers can seriously affect creatures such as fishes and
corals. (more about stingers on the Cnidria
Peacock Babies: They reproduce
by releasing eggs and sperm into the water. The larvae are tiny and
drift with other plankton before settling down to become a new cerianthid.
Cerianthids are also known to reproduce
asexually. Some can also reproduce by budding.
Peacock friends: Various animals may live with
a cerianthid. Small black feathery fanworm-like creatures called Phoronid
worms may be found near cerianthids. Is it said some small crabs
(Lissocarcinus laevis) also live inside the tube with the anemone
and some shrimps (Periclimenes sp.) are associated with the
Human uses: Cerianthids are sometimes
taken for the live aquarium trade. However, they do not make good
tank mates as their floating stingers affect other creatures in the
tank. Their burrowing habit and long body columns means they require
deep tank beds. They also only take suspended food. This makes them
difficult to keep alive in a home aquarium.
Status and threats: Cerianthids
are not listed among the threatened 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.
An inner ring of shorter tentacles
identifies this as a cerianthid.
Pulau Semakau, Apr 08
Long body column that slips
into an even longer tube.
Changi, Jun 03
At low tide, bundles its tentacles together.
Pasir Ris Park, Jul 08
Chek Jawa, Apr 12
captured a shrimp!
Chek Jawa, Sep 11
black Phoronid worms are often
seen with cerianthids.
Changi, Jun 03
hiding next to cerianthid.
Changi, May 11
on a cerianthid tube: eggs?
Changi, May 11
of crabs on a cerianthid.
on Singapore shores
Ceriantharia recorded for Singapore
Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity
commonly seen awaiting identification
are difficult to positively identify without close examination.
On this website, they are grouped by external features for convenience
- 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.