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Diploblasts
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Cnidaria and Ctenophores: Feeding, Defense, Sensory Organs, Phylogenetic Position, Human Interactions.
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InvertebratesWeek 11
Dr Francoise Mazet
Diploblasts
Diploblastic Animals; Cnidaria and Ctenophores:
- Eumetazoa; multicellular, sexual reproduction, embryonic development [gastrula
stage], true tissues which are organized into germ layers, highly differentiated
structures.
- Diploblasts; two germ layers separated by a gelatinous layer [mesoglea] and express
radial symmetry
- Triploblasts; three germ layers and show bilateral symmetry.
Cnidaria;
- Jelly fish, sea anemones, corals, hydra and myxozoas
- Elusive isolated aquatic habitats [sea water]
- 5 classes, 11,000> species
a. Anthozoa
b. Staurozoa
c. Scyophozoa
d. Cubozoa
e. Hydrozoa
- Two adult body forms;
a. Medusa [mouth and tentacles = swimming] Clade; Medusozoa Classes [b, c, d, e]
b. Polyp [mouth and tentacles above = sessile, attached to substrate via pedal disk.
Clade: Anthozoa // Classes; hexacorallia, octocorallia, hydrozoa
- Specific features;
1. radial symmetry
2. differentiated cells and organs; Cnidae [stinging cells], nerve net, tentacles,
contractile cells
3. gastrovascular cavity; only one opening and surrounded by tentacles
- Cnidarian Development;
o Sexual reproduction; gametes develop into gonads [found in either cell
layer] // hermaphroditism not common but can occur // planula are free-
swimming, ciliated [few mm
long], some have a mouth to
feed; others don’t.
o Asexual reproduction;
development of fully formed
individual via budding
[strobilation]
o Bilaterian symmetry of
cnidarian planula [flat body
with bilaterian symmetry;
evidence that bilaterian
evolved before apparition of
triploblastic bilaterian
organisms]
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