Cephalopods
Cephalopods History
• appeared some time in the late Cambrian
several million years before the first
primitive fish began swimming in the
ocean
• Scientists believe that the ancestors of
modern cephalopods (Subclass
Coleoidea: octopus, squid, and cuttlefish)
diverged from the primitive externally
shelled Nautiloidea (Nautilus) very early perhaps in the Ordovician, some 438
million years ago.
• Cephalopods were once one of the
dominant life forms in the world's
oceans
• Today there are only 650 or so living
species of cephalopods (compare that
with 30,000 living species of bony fish).
However, in terms of productivity, some
scientists believe that cephalopods are
still giving fish a run for their money
• Cephalopods are fast swimming predatory
animals, extremely intelligent
• Cephalopods foot is divided into tentacles
– squid=10 tentacle
– octopus=8 tentacle
– cuttle fish=6 or more tentacle
Cephalopods distinctive
structures
• Cephalopods have large, well developed eyes that
form images
• Tentacles are covered with suckers for seizing and
holding prey
• Cephalopods have a rasp like structure in their
digestive tract called a radula for breaking down food
• Cephalopods mouth has two strong beaks for tearing
its prey apart.
• Cephalopod is fitted with a funnel like structure that
fills with water and ejects it acting like a jet propulsion
More distinctive characteristics:
• They are able to change multi colors
• Can expand and contract pigment cells in its
skin
• Chromatophores(color cells) give the
cephalopod the ability to change.
• Can eject ink when alarmed causing the
enemy to be temporarily blinded. The ink
also inactivates predators chemical
receptors used for detecting prey.
Cephalopods diet
• Feed on crabs, shrimp, fish, and other
cephalopods
Cephalopods Habitat
• Intertidal to abyss
• Polar to tropics
• In other words they are found everywhere
Most common Cephalopods
•
•
•
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Squid
Cuttlefish
Octopus
Nautilus
Who belongs to the group?
• A cephalopod is any member of the
molluscan class Cephalopoda :"headfeet".
• These exclusively marine animals
are characterized by bilateral body
symmetry, a prominent head, and a
set of arms or tentacles (muscular
hydrostats) modified from the
primitive molluscan foot.
• The class now contains two, only distantly
related, extant subclasses: Coleoidea,
which includes octopuses, squid, and
cuttlefish; and Nautiloidea, represented by
Nautilus and Allonautilus. In the Coleoidea
the molluscan shell has been internalized or
is absent, whereas in the Nautiloidea the
external shell remains. About 800 living
species of cephalopods have been
identified. Two important extinct taxa are the
Ammonoidea (ammonites) and
Belemnoidea (belemnites).
Distribution
• Cephalopods are found in all the oceans of Earth.
None of them can tolerate freshwater, but the brief
squid, Lolliguncula brevis, found in Chesapeake
Bay may be a notable exception in that it tolerates
brackish water which has a low salinity.[5]
• Cephalopods occupy most of the depth of the
ocean, from the abyssal plane to the sea surface.
Their diversity is greatest near the equator (~40
species retrieved in nets at 11°N by a diversity
study) and decreases towards the poles (~5
species captured at 60°N).
Nervous system and behavior
• Cephalopods are widely regarded as the most
intelligent of the invertebrates and have well
developed senses and large brains.
• The nervous system of cephalopods is the most
complex of the invertebrates.
• The giant nerve fibers of the cephalopod mantle
have frequently been used as an experimental
material of neurophysiologists for many years;
their large diameter (due to lack of myelination)
makes them easier to study.
• Cephalopods are social creatures; when
isolated from their own kind, they will take to
shoaling with fish.
• Some cephalopods are able to fly distances
up to 50 m. While the organisms are not
particularly aerodynamic, they achieve these
rather impressive ranges by use of jetpropulsion; water continues to be expelled
from the funnel while the organism is in
flight.
Senses
•
Cephalopods have advanced vision, can detect gravity with statocysts, and have a variety of
chemical sense organs. Octopuses use their tentacles to explore their environment and can use
them for depth perception.
Vision and hearing
• Most cephalopods rely on vision to detect predators
and prey, and to communicate with one another.
Consequently, cephalopod vision is acute.
• Surprisingly—given their ability to change color—all
octopuses and most cephalopods are color blind.
When camouflaging themselves, they use their
chromatophores to change brightness and pattern
according to the background they see, but their ability
to match the specific color of a background may
come from cells such as iridophores and leucophores
that reflect light from the environment. They also
produce visual pigments throughout their body, and
may sense light levels directly from their body.
Vision and hearing
• Unlike many other cephalopods, nautiluses
do not have good vision; their eye structure
is highly developed but lacks a solid lens.
They have a simple "pinhole" eye through
which water can pass. Instead of vision, the
animal is thought to use olfaction as the
primary sense for foraging, as well as
locating or identifying potential mates.
• Cephalopods can use their statocyst to
detect sound
Use of light
• Most cephalopods possess chromatophores - that is,
coloured pigments - which they can use in a startling
array of fashions.
• As well as providing camouflage with their background,
some cephalopods bioluminesce, shining light
downwards to disguise their shadows from any predators
that may lurk below. The bioluminescence is produced by
bacterial symbionts.
• Bioluminescence may also be used to entice prey, and
some species use colorful displays to impress mates,
startle predators, or even communicate with one
another.It is not certain whether bioluminescence is
actually of epithelial origin or if it is a bacterial production
Body color
• Coloration can be changed in
milliseconds as they adapt to their
environment, and the pigment cells are
expandable by muscular contraction.
• Coloration is typically more pronounced
in near-shore species than those living in
the open ocean, whose functions tend to
be restricted to camouflage by breaking
their outline.