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Phylum: Brachiopoda
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Classes:Articulata
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Inarticulata
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Orders: 7 Articulate
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4 Inarticulate
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 Copy diagram on page
125 a) and b) Black to show
a typical articulate
brachiopod.
They have 2 VALVES
(shells) that totally enclose
the soft parts.
The average size is 20 - 70
mm but can range up to 370
mm.
The valves can open and are
hinged at one end; muscles
open and close the shell.
Morphology 2
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They usually allow water into
the shell, as they are filter
feeders extracting food from
seawater.
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The two valves are different
in size (as opposed to
bivalves).
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However; they do show a
line of lateral symmetry
along the middle of the
animal. Highlight this on
your diagram.
Morphology 3:Naming of the valves
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The smaller valve is the
BRACHIAL valve (upper in
life position).
The larger valve is the
PEDICLE valve (lower in life
position).
The animal secretes the
valves as it grows, the
original small shell is called
the UMBO and the shell
grows outwards from either
side of this point. Make sure
that you can see the umbo
on a hand specimen.
Morphology 4:
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Often the pedicle valve has a
small circular opening
(FORAMEN) at the end
through which a type of foot
extends called the
PEDICLE. Make sure that
you can see the foramen in
a hand specimen.
The pedicle allows the
brachiopod to attach itself to
the sea floor.
Inside the shell the body fills
much of the body cavity.
Morphology 5:
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Some shells like rhynchonellids
have a wrinkly COMMISURE
with FOLDS (one on either
side of the sulcus) and a
SULCUS (in the middle).
Draw a rhynchonellid showing
the fold and sulcus and the
inhalent and exhalent currents.
Folds have inhalent and sulcus
has the exhalent.
The currents are therefore
separated.
The crenulated commissure
also provides a greater surface
area.
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The inside of the shell is the
MANTLE CAVITY and is mainly
the LOPHOPHORE, which is a
food gathering and waterfiltering device.
 Draw diagram (d) from
page 125 Black.
The important muscles are:
At the posterior end is the
pedicle “foot” type of
ligament/muscle which when
extended could usually reach
outside of the shell.
The main muscles were the
ADDUCTOR and DIDUCTOR
muscles, which were used to
close the shell.
Internal morphology 2:
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 Draw diagrams from page
125 Black:
c) for muscle position.
e) and f) showing internal views
of shells with muscle scars.
Both sets of muscles were
attached to the shell and
although not preserved in the
fossils there are scars left from
where the muscles were
attached to the shell.
The CARDINAL PROCESS and
HINGE acts as a fulcrum on
which the muscles can pull.
The diductor muscles contract
and pull down the cardinal
process and open the shell.
Internal Morphology 3:
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As the diductor muscles
relax the adductor muscles
contract and close the shell.
Role of the lophophore is to
act as a feeding device,
which collects suspended
particles.
Some brachiopods like
spiriferids have a spiral
calcite support called a
lophophore support or
spiralia.
Draw diagram d on page
137.
Internal morphology 4:
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On the diagram you can see
that the brachiopod has
TEETH (pedicle valve) and
SOCKETS (brachial valve).
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What do you think the role of
these are?
Articulate Brachiopod Orders:
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There are 7 orders.
(including Productids).
For each draw a simple
diagram.
Make a note of the type
of hinge line:
Long or
Short
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They tended to live in
shallow marine conditions
(up to 500 m but may go
down to 6, 000m).
Modern forms live in cool temperate waters around the
Pacific (Japan, S. Australia,
New Zealand, N. Atlantic and
W. Scotland).
As there are modern day
equivalents we know their
environments and so they
are good palaeoenvironment
indicators (index fossils).
Index fossils etc.
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Define an index fossil:
A fossil that is restricted to a
particular
palaeoenvironment.
Corals mare perhaps the
best index fossils.
The most common
question regarding
Brachiopods is how to tell
the difference between
them and Bivalves.
We will cover this next when
we look at Bivalves.
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Brachiopods are a long-lived
Phylum ranging from the
Cambrian to Present.
They were very common in
the Palaeozoic and slightly
less so in the Mesozoic but
still remain important.
In the Present not many
forms are left with
approximately 70 Genera.
Over 2500 fossil Genera are
known.
The largest were found in
the Cambrian (370 mm).
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Brachiopods - Geology Rocks