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Phyla Cnidaria and Ctenophora
Lee-Mervin Mentoor,
Department of biodiversity and conservation biology
University of the Western Cape
Available at http://planet.uwc.ac.za/nisl/Eco_people/Presentations/
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
Organization in Radiates
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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
Organization (cont.)
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Also have epidermal and gastrodermal tissue
It’s movement allow food capturing and
locomotion
No specific tissue for circulatory,respiratory or
excretory purposes
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
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
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
Development in cnidaria
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Two body types are present
1)polyp: sessile form without tubular
body,polyoid mouth surronded by
tentaclesand attached to subtsratum
2)medusa:inverted shape of polyp, and freeswimming form,mouth is situated centrally in
concave body.
Medusa turn to polyp form when attache to
solid substrates
Different classes in cnidaria
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4 classes
1)hydroza-called hydroids;very small;have
medusa and polyps phase;2700 spp.
2)Scyphozoa-jellyfishes;dormant medusa;in
coastal; 200 spp.
3)cubozoa-box jellies;smaller then
jellyfishes;have squere-shaped bell;well
developed eyes;15 spp.
Classes in Cnidaria(cont)
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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.
Phylum Ctenophora
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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.
Classes in Ctenophora
Class Nuda
No tentacles
 Genus boroë are example
 Prey on jelly and other Ctenophores
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Class Tentacula
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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
Life Cycle of Ctenophores
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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
References
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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/PhylumCnidaria
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