Phyla Cnidaria and Ctenophora

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Phyla Cnidaria and Ctenophora

• Lee-Mervin Mentoor,
• Department of biodiversity and conservation
  biology
• University of the Western Cape

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Introduction

• Fossils of these phyla date back to Upper
  Paleozoic
• They were then classified under one phylum
  (coelenterata)
• Have may features that they share, but some
  important once that separate them
• Seperated on basis of symmetry from other
  metazoan organisms
• Because of there radial symmetry refferrd to as
  radiata

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Organization in Radiates

• Share developmental and morphological features
• Better organized organisms in the metazoan
• Possesses a mouth and coelentera which sponges do
  not have
• Allow larger food particle digestion
• Outer epidermis, inner gastrodermis and mesoglea
  distinct

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Organization (cont.)

• Also have epidermal and gastrodermal tissue
• Its movement allow food capturing and locomotion
• No specific tissue for circulatory,respiratory or
  excretory purposes

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Reproductivity in Radiates

• Utilize both sexual and asexual reproductive
  modes
• When gametes form, its left for fertilization
• Fertilized egg develop into solid ball of cells
  called planula.
• Its development varies in different organisms

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Morphological features of radiata

• Both radially organized and soft-bodied
• Uses flexible tentacles to bring food to oral
  cavity
• Body structure allow shape variation
• Lack of had part slow movement
• Mesogleal tissue increase with growth and they
  are unable to use gastric cavity for hydrostatic
  purposes

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Phylum Cnidaria

• Most common of the two and very diverse
• About 10,000 spp. Is known
• Simplest metazoans and possesses only mouth and
  stomach
• Specialized cells(cnidocytes) contain nematocysts
  which they use to immobilize prey
• Nematocyst have poisonous fluid and are used in
  defense and offense

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Development in cnidaria

• Two body types are present
• 1)polyp sessile form without tubular
  body,polyoid mouth surronded by tentaclesand
  attached to subtsratum
• 2)medusainverted shape of polyp, and
  free-swimming form,mouth is situated centrally in
  concave body.
• Medusa turn to polyp form when attache to solid
  substrates

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Different classes in cnidaria

• 4 classes
• 1)hydroza-called hydroidsvery smallhave medusa
  and polyps phase2700 spp.
• 2)Scyphozoa-jellyfishesdormant medusain
  coastal 200 spp.
• 3)cubozoa-box jelliessmaller then
  jellyfisheshave squere-shaped bellwell
  developed eyes15 spp.

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Classes in Cnidaria(cont)

• 4)Anthozoa(corals and anenomes)
• solitery or colonial with no medusa,
• stinging cells divide digestive cavity of polyp
• Hard skeleton with carbonate protect coral polyp
• Form corals
• About 6500 spp.

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Phylum Ctenophora

• Smallest of the two and exclusively marine
  invertebrates
• Specimens not easily collected(delicate)
• Tentacles and mouth absent
• One species have nematocysts for defense
• Use colooblast for prey capturing
• Two classes that is hermaphordidic
• About 100 spp.

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Classes in CtenophoraClass Nuda

• No tentacles
• Genus boroë are example
• Prey on jelly and other Ctenophores

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Class Tentacula

• Two tentacles which develop into specialized
  sheats
• 1,2 tentacles present in reduced forms
• Exaple are gooseberries-Atl. And Pac. Coast
• Other genuses include maemiopsis, cestum present
  in upper atl and tropical water

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Life Cycle of Ctenophores

• Simple life cycle carried out in plankton
• Most are hemaphordidid(one carry both egg and
  sperm)
• Egg left to be fertilized and then delop into
  larval stage
• Hatches and mature

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References

• 1)Stricberger, MW.1990. Evolution.Jones and
  artlettpublishers Inc.Bostos
• 2)Martindale MQ,Finnerty J and Henry JQ.The
  radiata and the evolutionary origin of bilateria
  body plan.Unpublished. 20 November 2001. USA
• 3)www.en.wikipedia.com
• 4)www.fossilmuseum.net/tree_of _life/PhylumCnidari
  a
• 5)www.fossilmuseum.net/GeologicalHistory.htm
• 6)www.nearctic.com/nathist/miscanim/cnidaria.htm
• 7)www.palaeos.com/invertebrates/Cinadaria/Cnidaria
  .htm
• 8)www.sos.bang.ac.uk/modules