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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
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).

slide2

CLASS : ANTHOZOA (CORALS)

  • The polyps are solitary or colonial.
  • The soft parts are divided into 6, 8 or more.
  • Often have a bilateral symmetry.
  • Marine.
anthozoan morphology
ANTHOZOAN MORPHOLOGY:
  • 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
SOFT PARTS:
  • 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)
slide5
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.
slide6

SUBCLASS: RUGOSA

  • 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).
slide7

SUBCLASS: RUGOSA

  • 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
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.
colonial compound rugose corals9
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:

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 corals10
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
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.
slide12

GEOLOGICAL HISTORY:

  • 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.
slide13

SUBCLASS: TABULATA:

  • 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.
slide15
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
Tabulate Corals To Know
  • Favosites:
  • Upper Ordovician - Devonian.
  • Draw:
  • Halysites:
  • Ordovician to Silurian.
  • Draw:
favosites
FAVOSITES:
  • 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
HALYSITES:
  • 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.
slide19

GEOLOGICAL HISTORY:

  • 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.
slide20

ORDER: SCLERACTINIA:

  • Solitary or compound corals.
  • Some still exist.
slide21

ORDER: SCLERACTINIA:

  • 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.
slide22

ORDER: SCLERACTINIA:

  • 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.
slide23

ORDER: SCLERACTINIA:

  • 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.
slide24

GEOLOGICAL HISTORY:

  • 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.
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