phylum cnidaria n.
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PHYLUM: CNIDARIA. Classes of Cnidaria. Class Hydrozoa (e.g., Hydra, Obelia ) Class Scyphozoa (e.g., Aurelia ) Class Cubozoa (e.g., cube jellies) Class Anthozoa (anemones and corals) Subclass Hexacorallia (sea anemones, hard corals) Subclass Octocarallia (sof corals).

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classes of cnidaria
Classes of Cnidaria
  • Class Hydrozoa (e.g., Hydra, Obelia)
  • Class Scyphozoa (e.g., Aurelia)
  • Class Cubozoa (e.g., cube jellies)
  • Class Anthozoa (anemones and corals)
    • Subclass Hexacorallia (sea anemones, hard corals)
    • Subclass Octocarallia (sof corals)
general characteristics
General Characteristics
  • Entirely aquatic; mostly marine, but with a few freshwater species;
  • may be solitary or colonial
  • Metazoan, with true tissues.
  • Diploblastic – two germ layers
    • outer cell layer known as ectoderm (epidermis),
    • inner cell layer known as endoderm (=gastrodermis),
    • with a non-cellular mesoglea between.
general characteristics1
General Characteristics
  • The internal body space (gastrovascular cavity) lined with gastrodermis
  • has a mouth, but no anus (incomplete digestive tract)
  • Possess cnidocytes with special cell organelles - nematocysts, used for defense and offense
general characteristics cont
General Characteristics cont.
  • Phylum exhibits polymorphism
    • Metagenesis- alternation of generation
  • Polyp (often sessile) and the medusa (free swimming).
  • The polyp stage reproduce asexually, while the medusa stage usually reproduces sexually
  • Reproduction is asexual by budding and/or sexual, producing a ciliated planula larva
figure 13 02
Figure 13.02

Two general

body forms

class hydrozoa
Class Hydrozoa
  • solitary or colonial
  • alternation of asexual polyps and sexual medusae

Life Cycle of Hydra





hydra c s



Hydra c.s.




figure 13 091
Figure 13.09

Obelia Life Cycle

obelia medusa
Obelia - Medusa



Gastrovascular cavity

obelia hydroid colony
Obelia – Hydroid colony

Gastrozoids = Hydranth

Gonozoids = Gonangium

obelia hydroid colony1
Obelia – Hydroid Colony



physalia portuguese man o war a colony not an individual
Physalia –Portuguese Man-O-War - a colony, not an individual

It is not a jellyfish!!

class scyphozoa true jellyfishes
Class ScyphozoaTrue Jellyfishes
  • polyp stage reduced or absent
  • bell-shaped medusae
  • margin of bell with eight notches which are provided with sense organs
  • all marine
class anthozoa sea anemones and corals
Class – AnthozoaSea Anemones and Corals
  • all species occur as polyps only, no medusae;
  • gastrovascular cavity partitioned by at least eight septa with nematocysts
  • Solitary or colonial
  • all marine.
phylum ctenophora

Phylum Ctenophora

The Combjellies

general characteristics2
General Characteristics
  • Biradial symmetry
  • Eight rows of comb plates
  • Tentacles possess colloblasts
  • Triploblastic (three cell or germ layers)
  • Mesoglea (loose mesenchyme) is jelly-like material strews with fibers and amebocytes and contains true muscle cells
  • Aboral sense organ (statocyst)
  • Digestive system: mouth, pharynx, stomach, branched canals and anal pore
  • Monoecious, with both eggs and sperm produced from endodermal lining of digestive canals beneath comb plates