All of the major phyla of
animals are represented
in the plankton.
Remember: In the sea,
microscopic plantlike
organisms form the base
of the food chain.
This means most of
the organisms that
feed on these plant
like organisms are also
small.
With such a wealth of
microscopic food,
organisms take
advantage of this rich
food supply either as a
larval form or as an
adult.
Some of these organisms
are herbivores feeding on
the microscopic plants.
Some are predaceous
carnivores which feed on
the herbivores or other
carnivores.
Those organisms that
spend their entire life
as plankton are called
holoplankton.
Those organisms that
spend part of their
life as plankton are
called meroplankton.
Copepods are the
most abundant of
the animal
plankton types.
They are
Crustaceans that
feed near the
base of the food
chain on diatoms.
Copepods posses a
single, small
compound eye
and two jointed
antennae.
Copepods also
have a larval
stage that can be
very common in
plankton samples.
In Fact, many of
the marine
crustaceans have
a planktonic
Nauplius stage.
Shrimp Like Plankton
Two shrimp like
organisms are
often found in
plankton
samples…
Mysids and
Euphausids.
Shrimp Like Plankton
Large swarms of
euphausids or Krill
are often found in
nutrient rich cold
waters. There,
they form an
important part of
the food chain.
Cladocera
This group of
planktonic
Crustaceans is
best known by
the Daphnia or
water flea.
Cladocera
Cladocera have a
large anterior,
compound eye
and an enlarged
carapace.
Cladocera
As can be seen
here, the female
carries the
fertilized eggs
within the
carapace.
Ostracods
These
Crustaceans have
a large, bivalve
carapace. They
are often nick
named “bean
clams” or “mussel
shrimp”.
Coelenterata (Cnidaria)
Many forms of
coelenterates
can be found in
the plankton.
In fact, all three
classes have
some
representation.
Coelenterata (Cnidaria)
Although large,
most consider
the
macroscopic
jellyfish to be
part of the
plankton.
Coelenterata (Cnidaria)
The Box jellyfish or
Sea Wasp is found
off the Northern
Coast of Australia.
It is the most
dangerous
jellyfish!
Coelenterata (Cnidaria)
There are many
microscopic
forms in the
plankton. These
are often
juveniles of
larger
organisms.
Coelenterata (Cnidaria)
You might also
find this Planula
which is the
larval form of
members in this
phylum. This
example has
been stained.
Ctenophora
Known as the comb
jellies, these
macroscopic
organisms swim
with their 8
cilliated rows.
Many, are about
the size of a
baseball.
Arrow-worms
Chaetognaths or
arrow-worms are
often found in
plankton samples.
About 1-5 mm in
size, they are
predaceous
carnivores.
Protists
There are protists that can
be found in plankton
samples. The three most
common all have shells.
Their shells are often
found in marine sediments.
Tintinnids
Tintinnids are marine
protists that
secrete a vase-like
shell or lorica that
protects them when
they withdraw.They
are filter feeders.
Foraminifera
Forams are
amoeba like
organisms that
have a
calcareous shell.
These shells are
very important
in marine
sediments.
Radiolaria
Radiolarians are amoeba
like organisms with a
skeleton formed of
silica. They are
common in colder
waters where there
shells can dominate
the sediments.
Meroplankton
Remember, these are
organisms that only spend
part of their lives in the
plankton. Most become
benthic or bottom dwelling
organisms as adults.
Barnacle Nauplii
Barnacles spend their
adult life firmly
attached to an
object in the water.
They kick food in
their mouths that’s
filtered out of the
water.
Barnacle Nauplii
Barnacle nauplii are
often common in
inshore samples.
Barnacles go from
this stage to a
settling cypris stage
and then to the
sessile adult stage.
Veliger Larvae
Mollusks have
several planktonic
stages. They have
a ball like
trochophore stage
and a veliger stage.
Veliger Larvae
Often, you can
find the shells of
these immature
mollusks in
plankton samples.
Zoea
Crabs, like many
Crustaceans have
a larval stage
known as a zoea.
At certain times
of the year it can
dominate the
samples!
Megalopa
The megalopa
stage
resembles the
adult and will
soon settle to
the bottom.
Echinoderm Larvae
Echinoderms have a
bilateral larval
stage that can
often be found in
near shore samples
of plankton.
Fish Larvae
Larval fish are
often part of
the plankton.
Fish Eggs
Even fish
eggs can be
found in the
plankton
samples.