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Cnidarians

Cnidarians. Cnidarians - General Characteristics. Diverse: ~10,000 living species described. cnidoblasts unique to this phylum.  Contains Nematocyst. Threads may wrap, stick, or poison. Cnidarians - General Characteristics. Body plan:

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Cnidarians

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  1. Cnidarians

  2. Cnidarians -General Characteristics • Diverse: ~10,000 living species described. • cnidoblasts unique to this phylum.  Contains Nematocyst. Threads may wrap, stick, or poison

  3. Cnidarians -General Characteristics • Body plan: • gelatinous layer (mesoglea) between inner and outer tissues usually with scattered cells and collagen fibers. • Distinct internal cavity with a single opening (enteron) • The mouth is often, but not always, surrounded by a ring of tentacles.

  4. Cnidarians -General Characteristics

  5. Cnidarians -General Characteristics • rudimentary ‘nerve-nets’ • Sensory organs: • Statocysts and ocelli. • lack circulatory and respiratory structures

  6. Cnidarians –Life History • solitary or colonial • All aquatic, most marine • primarily carnivorous, but some filter-feed on phytoplankton, and some with endosymbiotic algae • May have symbiotic relationships with other species as well: • "A" Portuguese man-of-war is • composed of various types of polyps • for feeding, reproduction • and buoyancy.

  7. Cnidarians -Reproduction • Asexual and sexual. • Cnidarians have acquired a bi-morphic life-style: • sessile polyp, which is attached to the substrate, • a free-swimming/floating medusa

  8. Cnidarians –Major Classes • Class Hydrozoa • Typically display alternation of generations, polyp (asexual) and medusal (sexual),though some only exist as polyps (e.g. hydra)  • No cells in mesoglea • No nematocysts in gastrodermal tissue • fire "corals“ • Freshwater "jellyfish" • Craspedacusta sowerbii • Obelia (a hydroid)

  9. Cnidarians –Major Classes • Class ScyphozoaThe true jellyfish • Medusa stage predominates and most  inhabit the water column in medusa stage. • extensive gastrovascular canal systems

  10. Cnidarians –Major Classes • Class CubozoaSmall class in size and diversity and recently considered in a different order than Scyphozoa • approximately cuboid in shape • margin of the bell is frequently turned inward • feed predominantly upon fish and can even kill humans! • Sea Wasp (Chironex fleckeri)

  11. Cnidarians –Major Classes • Class Anthozoa ‘flower animals’ contain majority of cnidarian species • enteron (coelenteron) is divided  into a succession of paired vertical partitions. • simple net. Why so simple? • no medusal stage; sessile or  colonial except for planktonic planula larval stage • asexual budding is extensive in colonial forms and some  secrete a  supportive skeleton of calcium carbonate or chitinous material.  Not many other types of organisms have so altered the landscape.

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