you learn only 3 things about them ...
are molluscs but (except the Natilus) lack external shells.
move by jet-propulsion and have many arms.
Most can rapidly change their colours and even skin texture.
Cephalopods can be commonly seen on many of our shores. Octopuses,
in particular, are far more common than most people would imagine.
They are usually well hidden or camouflaged. Cuttlefishes too are
common, especially small ones. Squids and large cuttlefishes, however,
appear to be only seasonally common.
What are cephalopods? Cephalopods
are molluscs (Phylum Mollusca) like snails,
slugs and clams. The Class Cephalopoda include octopuses,
squids and cuttlefishes. Another
member of this group are the nautilus shells.
Cephalopods are generally fast moving, many-armed hunters. Quite different
from the more typical snails, slugs
and clams that we think of as molluscs.
There are nearly 800 species of cephalopods.
No Shells: Aside from
the nautilus, other cephalopods have no external shells. Octopuses
have no shells at all. Squids and cuttlefishes retain a small internal
shell which helps to stiffen their bodies and in cuttlefishes, to
Cunning Cephalopods: All cephalopods
are carnivorous hunters. As predators, most cephalopods have a well-developed
brain and keen eyesight. Most have eyes similar in structure to vertebrates
Armed and Dangerous: 'Cephalopoda'
means 'head foot'. Indeed, instead of a single broad foot like other
molluscs, the foot of the cephalopod has become adapted into many
long and flexible arms, lined with rows of suckers. A nautilus may
have 90 such arms, while octopus, squids and cuttlefishes have 8.
The mouth lies in the middle of the arms; thus their arms can be considered
'super-lips'. Most cephalopods retain a radula, and all have a sharp
two-part beak, like a bird's. These are used to tear their prey into
smaller pieces. Some squids and octopuses can inject a toxin with
their bites. Their digestive systems are adapted for rapid digestion.
They also have a well-developed blood circulatory system to support
their more active life-style.
Arms vs tentacles: All cephalopods
have 8 arms. In addition to these arms, squids and cuttlefish have
a pair of tentacles. Tentacles have suckers only at the tips (arms
have suckers throughout the length) and the tentacles are used in
a special way. More details on the page about squids
Jet-powered Molluscs: Cephalopods
can zoom about quickly with jet-propulsion. They forcefully squeeze
water out of their mantle cavity (a cavity in their body) through
a flexible funnel and shoot off in the opposite direction. The funnel
can be pointed in different directions to control their movement.
Squids and cuttlefishes also have fins along their bodies to control
Disappearing Ink: Many octopuses,
squid and cuttlefish can squirt ink that distracts predators and clouds
up the water. The ink might be combined with mucus to form an ink-blot
that holds its shape for a while in the water. This ink-blot decoy
distracts the predator while the cephalopod makes its escape. The
ink may also contain substances that affect the senses of other sea
creatures. The ink contains melanin, the same pigment that colours
our skin. It is produced in a special gland embedded in the liver.
Another organ produces the mucus to mix with the pigment. Jets of
water from the funnel direct and shape the pigment and mucus into
a shape that suits the cephalopod's purposes.
Colourful Cephalopods: Octopuses,
squids and cuttlefishes have complex skin that can instantly change
colour. Octopuses and cuttlefishes can also change the texture of
their skin, creating bumps, flaps, fingers and other projections to
match their surroundings. Many squids are also bioluminescent.
The rapid colour and pattern changes are achieved by controlling chromatophores,
groups of cells that contain pigments which the animal can rapidly
change in size and shape. Beneath the chromatophores are iridophores,
layers of platelets made of chitin or proteins which produce the metallic
green, blue, gold and silver colours by reflecting light. Iridophores
are found in cuttlefish, some squids and some octopuses.
Social Cephalopods: Cephalopods
have relatively well-developed behaviour for interacting with each
other. This involves colours changes and postures during courtship,
mating and territorial disputes.
Cephalopod Babies: Cephalopods
have separate genders and practice internal fertilisation. The male
usually has some sort of modified arm to insert his sperm packet into
the female. She later uses the sperm to fertlise her eggs which are
usually laid in capsules or cases.
These do not hatch into free-swimming larvae but into miniatures of
the adults. However, some of these tiny juveniles might drift with
the plankton for a while. Most cephalopods don't live long; about
1-2 years, dying soon after they reproduce.
Human uses: People everywhere
enjoy eating cephalopods. Cephalopods are also much studied for a
better understanding of human anatomy.
Status and threats: None of our
cephalopods are listed among the threatened animals of Singapore.
However, like other marine creatures, molluscs are vulnerable to habitat
loss due to reclamation or human activities along the coast that pollute
the water. They are also vulnerable to trampling by careless visitors
and over-collection for food can affect local populations.
Sisters Island, Jul 04
A pair of tentacles to grab prey
. Pulau Hantu, Aug 03
Chek Jawa, May 03
of black egg capsules
Changi, Jul 02
Baby cephalopods emerge from
their egg capsules as miniatures of the adults
Changi, Jul 03
Tan, Leo W. H. & Ng, Peter K. L., 1988. A
Guide to Seashore Life. The Singapore Science Centre,
Singapore. 160 pp.
- P. Jereb
and C.F.E. Roper (editors). Chepalopods of the World. FAO Species
Catalogue for Fishery Purposes No. 4, Vol.
1 and Vol.
Cephalopod Page by Dr James B Wood on the Dalhousie University
and the University of Texas Medical Branch website.
- From the
wild shores of singapore blog.
- M. D. Norman, J. Nabhitabhata & C. C. Lu. 29 June 2016. An updated checklist of the cephalopods of the South China Sea. The Raffles Bulletin of Zoology 2016 Supplement No. 34 (Part II of II) Pp. 566-592.
- 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.
- 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.
- Norman, Mark
and Helmut Debelius, 2000. Cephalopods:
A World Guide.
ConchBooks, Germany. 319 pp