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CNIDARIA Phylum: Cnidaria: formerly called Coelenterata - PowerPoint PPT Presentation

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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). CLASS : ANTHOZOA (CORALS).

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Cnidaria: (formerly called Coelenterata)


Anthozoa: (corals)

Hydrozoa: (hydroids)

Scyphozoa: (jellyfish)




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.

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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.

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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 byRADIAL 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.


  • 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)

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Colonial/Compound Rugose Corals

  • 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.

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Colonial/Compound Rugose Corals

  • 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:


  • The individuals are not closely touching.

  • Fasciculate corals can be further sub divided:


  • They branch irregularly.


  • If the corallites are parallel to each other.

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Colonial/Compound Rugose Corals


  • All the corallites are in contact.

  • These are also further sub divided:


  • Polygonal corallites in cross section and they have a clear dividing wall.


  • The walls are absent.

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Mode of life and palaeoenvironment (Index Fossil)

  • 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

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Tabulate Corals To Know

  • Favosites:

  • Upper Ordovician - Devonian.

  • Draw:

  • Halysites:

  • Ordovician to Silurian.

  • Draw:

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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.

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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 large landmasses.