updated Oct 12
learn only 3 things about them ...
Octopuses are common on many of our shores. They are just
hard to spot.
They are among the most intelligent of invertebrates.
can bite. Don't touch them!
seen? Most people are surprised to hear that octopuses
are quite commonly encountered on many of our shores. Even the most
'beat up' looking shore eventually turns up a resident. They are generally
more common in areas with coral rubble, but may also be seen in seagrass
areas. You need patience and some experience, however, to spot an
octopus. These marvellous masters of camouflage are shy and generally
only active at night. During the day, they are often well hidden in
some cosy den. Some octopuses seen are as large as 1m across with
their arms outstretched. Others are tiny, less than 10cm across.
What are octopuses? Octopuses
are molluscs (Phylum Mollusca) like
snails, slugs and clams; and cephalopods
(Class Cephalopoda) which include squids and cuttlefish.
The correct plural term for octopus is octopuses and not octopi (Dr
James B Wood shares an
explanation why this is so).
Awesome Octopus: The octopus is
a hunter with many tricks. Among its formidable weapons is its brain!
The octopus is in fact considered the smartest known invertebrate.
It has a well-developed brain and excellent eyesight. Studies show
that the octopus can learn, not only by itself but also from one another!
Armed and Dangerous: An octopus
searches for prey mostly at night, spreading out its eight long arms
to feel into crevices for crabs, prawns, snails, clams and other such
morsels. The highly flexible arms have strong suckers to grip objects
so that the octopus can slowly 'creep' over the surface as it stealthily
investigates all hiding places (octopuses use jet propulsion when
they are in a bigger hurry, see below). The arms also have numerous
receptors sensitive to taste and touch.
The arms are joined together near the head with webbing. An octopus
uses this webbing like a net. For example, to envelope a little mound
of rubble where some small titbit might be hiding. When the prey attempts
to escape, it is literally surrounded by octopus! Prey is killed with
a bite of its sharp, hard beak. It is often then hauled back to the
octopus' den for a leisurely meal.
Octopuses bite! Although octopuses
have a hard beak and a radula (ribbon of teeth), they don't chew their
food. Digestive juices are injected into the prey which soften the
tissues. Some octopuses can drill a hole through a snailís shell to
get at it. Others crush shells and crack crabs with their hard beaks.
have a sharp, hard beak. Some can inject a toxin with
their beaks. The tiny Blue-ringed octopus (Hapalochaena
maculosa) is recorded for Singapore, but not
commonly seen. Still, it is best to avoid touching any
kind of octopus.
How to stay safe:
Wear covered footwear. Don't touch octopuses.
The octopus has three hearts. Besides the usual heart, it has two
additional hearts, each pumping extra blood through the gills. Its
blood is blue due to concentrations of copper-based pigments that
Shell-less but not helpless: Unlike
most other molluscs, the octopus does not have a shell at all. This
is actually an advantage as the octopus can then squeeze into all
kinds of impossibly tight hiding places. The octopus, however, has
many other ways to deal with danger.
In the first place, an octopus is generally very difficult to spot.
It can change its colours and even the texture of its skin to blend
with its surroundings. And change these rapidly as it moves to a new
When spotted, some octopuses make sudden drastic colour changes to
confuse the predator. They then zoom off using jet-propulsion; squirting
a jet of water out of a funnel to zoom off in the opposite direction.
When particularly alarmed, an octopus may release a cloud of ink to
disorient predators. The ink may contain substances that affect the
senses of other sea creatures. In the clouded water, the octopus makes
babies: Octopuses have separate genders. To mate, the male
uses a special arm called a hectocotylus to insert a sperm packet
into the female's body. While doing so, he usually keeps as far away
from the female as possible, and he is usually pale, a sign of stress.
The female uses the sperm to fertilise her eggs as she lays them.
In most octopus species, the eggs are laid in capsules attached to
hard surfaces. Here are some photos of cephalopod
In bottom-dwelling octopuses, the female looks after her eggs; keeping
them oxygenated, free of algae and bacteria, and defending them from
predators. Some even carry their eggs with them. The female does not
feed during this time and usually dies after the eggs hatch. Most
octopuses breed only once in their life, and many die after doing
The eggs do not hatch into free-swimming larvae. Instead, miniature
octopuses emerge. Some are rather well-developed and settle down soon
after hatching. Others may drift with the plankton before settling
down. Here's a photo
of a baby octopus on Image
Quest 3-D Marine Library.
Human uses: Octopuses are widely
eaten in Asia. They are caught in many ways, including by lines, in
pots or by trawling.
Status and threats: None of our
octopuses are listed among the endangered animals of Singapore. However,
like other creatures of the intertidal zone, they are affected by
human activities such as reclamation and pollution. Trampling by careless
visitors can also affect local populations.
web as a net to trap prey.
Pulau Hantu, Aug 04
The arms can stretch out to great length!
Sentosa, Jan 05
Underside is full of suckers.
Sisters Island, May 07
with its head above the ground.
Changi, May 09
Chek Jawa, Aug 05
Well camouflaged on hard coral.
Sisters Island, May 07
Sisters Island, Jul 04
These three photos are of the same animal ..
Sentosa, Jul 04
... taken minutes apart.
...with rapid colour and texture changes!
A pair of mating octopuses,
one pale and the other dark.
Sentosa, Jul 05
Tiny octopus among seaweeds.
Sisters Island, May 12
on Singapore shores
Octopodidae recorded for Singapore
Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist
of The Molluscs of Singapore.
Common names from Cephbase
seen awaiting identification
are almost impossible to positively identify without dissection
and examination of internal parts. On this website, they are
grouped by external features for convenience of display.
from Dr James B Wood about difficulties
in identifying octopuses
indicus (Old woman octopus)
Hapalochlaena maculosa (Blue-ringed octopus)
Octopus aegina (Marbled octopus)
Octopus australis (Hammer octopus)
Octopus vulgaris (Common octopus)
Tan, Leo W. H. & Ng, Peter K. L., 1988. A
Guide to Seashore Life. The Singapore Science Centre,
Singapore. 160 pp.
Cephalopod Page by Dr James B Wood on the Dalhousie University
and the University of Texas Medical Branch website: everything
you could possibly want to know about cephalopods. Lots of info,
photos, articles and links to cephalopods. Lots of fabulous photos,
a delightful and exhaustive FAQ, and lots of cool articles for
the laymen, as well as lesson plans.
by Dr James B Wood: a
database-driven website on all living cephalopods with species
search, image and video database, reference database and researcher
is this octopus thinking? by Garry Hamilton from New Scientist
7 Jun 97 on Lee Borrell's website: fascinating facts about the
learning ability of cephalopods
is the defense mechanism an octopus uses to spray its ink called?
on the Mad Scientist website:
Allison J. Gong explains more about this behaviour
do octopuses know what colour to be? on the Mad
Scientist website: Rochelle Ferris explains
do octopus die after mating? on the Mad
Scientist website: Trevor Cotton explains why this makes sense
does an octopus change its skin colour? on the Mad
Scientist website: Kimberley Sander explains how this can
be done quickly by an octopus, while other animals take longer
to do so.
- From the
wild shores of singapore blog
- Tan Siong
Kiat and Henrietta P. M. Woo, 2010 Preliminary
Checklist of The Molluscs of Singapore (pdf), Raffles
Museum of Biodiversity Research, National University of Singapore.
- Norman, Mark
and Helmut Debelius, 2000. Cephalopods:
A World Guide.
ConchBooks, Germany. 319 pp
Mark and Amanda Reid. 2000. A
Guide to Squid, Cuttlefish and Octopuses of Australasia
The Gould League of Australia. 96pp.
- 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.
- 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.
- 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.