cnidaria n.
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  1. 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).

  2. 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.

  3. 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.

  4. 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)

  5. 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.

  6. 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).

  7. 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)

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. Tabulate Corals To Know • Favosites: • Upper Ordovician - Devonian. • Draw: • Halysites: • Ordovician to Silurian. • Draw:

  16. 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.

  17. 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.

  18. 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.

  19. ORDER: SCLERACTINIA: • Solitary or compound corals. • Some still exist.

  20. 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.

  21. 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.

  22. 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.

  23. 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.