Transcript CORALS - Geology Rocks

CNIDARIA
Phylum:
Cnidaria: (formerly called Coelenterata)
Class:
Anthozoa: (corals)
Hydrozoa: (hydroids)
Scyphozoa: (jellyfish)
Sub-Classes:
Zoantharia:
Rugosa (extinct)
Tabulata (extinct)
Scleractina (reef building, still exist part of the
Zoantharia).
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The polyps are solitary or
colonial.
 The soft parts are divided
into 6, 8 or more.
 Often have a bilateral
symmetry.
 Marine.
ANTHOZOAN MORPHOLOGY:
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Corals are usually sack
shaped widest at the top
which contained the
MOUTH narrowing at the
base where it was
attached.
 Page 101 Copy Fig. 63a.
 Draw c and h on page 103
for a typical solitary coral.
 The body structure is
simple with a hard calcite
outer layer and an inner
body cavity.
SOFT PARTS:
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The soft parts are similar in all
the subclasses.
Page 114 Black Fig. 72a and
b (draw).
The body cavity is divided into
small segments by RADIAL
MESENTERIES (partitions)
which give it stability and
strength and provide more
efficient feeding.
Outer Layer = ECTODERM
Inner Layer = ENDODERM
The inner body cavity =
COELENTERON (ENTERON)
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Mesenteries help spread the
surface area of the coelenteron
and therefore help digestion of
food.
The MOUTH is usually towards
the centre and has a number of
functions:
Takes in food.
Allows discharge of waste.
Discharge of larvae.
The mouth is surrounded by
retractable tentacles, which
have stinging organs on them.
Some corals show a bilateral
symmetry but more commonly
show radial symmetry with parts
of the body repeated in the
coelenteron around the mouth.
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Middle Ordovician Permian.
Occur as solitary or
compound forms.
SOLITARY RUGOSE
CORALS:
Coraliteis conical in shape.
The skeleton grew upwards
from a narrow base.
The whole structure can be
straight or curved (horn
shaped).
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CALICE or the top of the
body appears like a
depression and in this
can be seen a central
region called the AXIAL
REGION.
 The ends of the SEPTA
can also be seen
sometimes.
 A COLUMELLA may be
present in the centre
(rod like)
Colonial/Compound Rugose Corals
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In colonial rugose
corals there are often a
large number of septa.
 TABULAE: These
represent former levels
of the calice floor,
secreted by the polyp
to seal off the lower
area of the corallum.
 They are best seen if
longitudinal sections
are cut.
Colonial/Compound Rugose Corals
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They are made up of varying
numbers of individuals each called
a corallite. Fig. 63 page 101 (OHP).
 They are subdivided based on the
relationship between the corallites:
FASCICULATE:
 The individuals are not closely
touching.
 Fasciculate corals can be further
sub divided:
DENDROID:
 They branch irregularly.
PHACELOID:
 If the corallites are parallel to each
other.
Colonial/Compound Rugose Corals
MASSIVE:
 All the corallites are in
contact.
 These are also further sub
divided:
CERIOID:
 Polygonal corallites in
cross section and they
have a clear dividing wall.
ASTRAEOID:
 The walls are absent.
Mode of life and
palaeoenvironment (Index Fossil)
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Sessile apart from when in
larval stage.
Benthonic and fixed.
lived in warm (22 - 29ºC
ideally 25ºC) tropical.
Shallow seas ideally <25 m
continental shelf.
They like clear water with little
sediment.
Well oxygenated, high energy.
Typically found in carbonate
rocks especially in the
Carboniferous.
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Appear in the middle of
the Ordovician but are not
common until the Silurian.
 Throughout the rest of the
Palaeozoic their numbers
increased.
 They reached their
maximum in the Lower
Carboniferous and then
gradually declined and
disappeared in the
Permian extinction.
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These are extinct
compound corals.
They have slender
corallites, which are
crossed transversely by
tabulae.
They have a calcareous
skeleton with usually small
individual corallites
although the whole colony
can be large.
Shape: either fasciculate
(no contact) or massive.
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The fasciculate forms can branch
irregularly.
In others the corallites are joined
laterally to form a chain like structure
approximately one corallite wide.
The calice is usually small being a
few mm in diameter and varying in
shape : round, oval or polygonal.
The septa are not always present but
number about 12 if they are present
and they are similar in size and
shape.
Tabulae are very numerous and
occur horizontally although some
appear domed.
Mural pores: small holes that connect
the corallite
Tabulate Corals To Know
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Favosites:
Upper Ordovician - Devonian.
Draw:
Halysites:
Ordovician to Silurian.
Draw:
FAVOSITES:
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Massive corallum, often a
hemisphere shape.
 The whole colony is usually fairly
small, maximum being 10 cm
across, rarely larger.
 Cerioid (polygonal) corallites which
are often quite long.
 Each calice is small: 2 - 3 mm in
diameter.
 The septa are often absent, if
present they form ridges.
 Tabulae are numerous and evenly
spaced.
 Most important in the Silurian.
HALYSITES:
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Phaceloid corallum giving an
almost chain like appearance as
corallites can be joined together
on two or three sides to form a
branching structure.
 Commonly called “chained
coral”.
 Septa are usually absent and
the tabulae are horizontal.
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Middle Ordovician to Permian
extinction.
Most abundant in the Silurian and
Devonian, then through the Upper
Palaeozoic the numbers decreased and
died out in the Permian extinction.
Most common in carbonate rocks e.g.
limestone, rarely found in muddy
sediments.
During the Silurian and Devonian
important reef formation and during this
time they were more numerous than
rugose corals.
Silurian: Favosites and Halysites
common.
Devonian: Favosites still common.
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Solitary or
compound corals.
 Some still exist.
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Draw figs 73 f and h Black
page 116.
 Their originally aragonitic
skeletons have
dissepiments, tabulae, and
septa just as in the rugosa.
 Although there are
superficial similarities,
scleractinian corals differ
from rugosa corals by their
skeletal mineralogy and by
their method of septal
insertion during growth.
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Scleractinian corals also have
six primary septa, but in
contrast to rugose corals,
subsequent septa are added in
all six of the resulting spaces.
An important distinction
between the two orders is that
for the Scleractinia the septa
are inserted between every two
pre-existing septa in later
growth stages.
Therefore have a repeated
radial symmetry and so
different from the Rugosa.
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Adjacent polyps can be
attached or connected
together via common soft
tissue.
They resemble sea
anemones.
The corallum of the
solitary corals is usually
conical or cylindrical.
In compound types there is
a much wider range of
sizes and shapes.
Use the same terminology
as used in rugose corals.
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Middle Triassic to Recent.
Most important in the Jurassic.
Not very important in the
Cretaceous but can be found in
the Chalk in particular solitary
forms.
In the Tertiary there are a few
reef-building forms and more
recently in the Quaternary cup
like corals are more common.
In the present they form important
reef building animals in the
tropics and sub tropics around
ocean islands and east coasts of