What Characteristics Account for the Great Success of Cnidarians ...
What Characteristics Account for the Great Success of Cnidarians ...
What Characteristics Account for the Great Success of Cnidarians ...
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<strong>What</strong> <strong>Characteristics</strong> <strong>Account</strong> <strong>for</strong><br />
<strong>the</strong> <strong>Great</strong> <strong>Success</strong> <strong>of</strong> <strong>Cnidarians</strong>?<br />
1. Two distinct adult <strong>for</strong>ms<br />
2. Diphasic life cycle in some species<br />
3. Ability to proliferate by cloning<br />
4. And to <strong>for</strong>m polymorphic colonies<br />
5. Formidable prey capture device<br />
6. Low Energy Demands<br />
Diversity <strong>of</strong> <strong>Cnidarians</strong><br />
3 Main Taxonomic classes<br />
Class Scyphozoa<br />
Class Anthozoa<br />
Class Hydrozoa<br />
Class Cubozoa contains<br />
a few jellyfish spp<br />
Similarities <strong>of</strong> Polyp and Medusa<br />
1
Epi<strong>the</strong>leomuscular<br />
cells<br />
cnidocytes<br />
Nutritive<br />
muscular<br />
cells<br />
Gland<br />
cells<br />
mesoglea<br />
Epi<strong>the</strong>liomuscular Cells<br />
and gastromuscular cells<br />
Lacking mesoderm, but muscles derived<br />
from epi<strong>the</strong>lial endodermal and ectodermal cells<br />
How is it that organisms as different<br />
As jellyfish, hydroids and anemones<br />
Can be classified in <strong>the</strong> same phylum?<br />
1. Nematocysts: unique stinging cells<br />
2. Diploblastic: 2 cell layers separated by acellular<br />
mesoglea (“middle jelly”); epi<strong>the</strong>liomuscular cells<br />
3. Primary radial symmetry<br />
4. No head, no CNS, no circulatory or excretory<br />
systems and no discrete respiratory structures<br />
5. Dimorphism <strong>of</strong> adult <strong>for</strong>m; in life cycle<br />
6. 2- way digestive system<br />
7. nerve net<br />
2
Giant jellyfish invade Japan<br />
Hydromedusa <strong>for</strong><br />
comparison<br />
Seven synapomorphies:<br />
Life history (4): large size, rapid growth, high fecundity,<br />
asexual reproduction by polyps<br />
Morphology (1): strong swimmers/ High Reynolds number<br />
Diet (2):: varied diet/specialize on microzooplankton,<br />
(have rizhostome tentacles); lack <strong>of</strong> symbionts<br />
• Small a few cm<br />
• Velum to aid in locomotion<br />
• Radial canals unbranched<br />
• Simple epidermal and endodermal nerve net<br />
• Nematocysts usually small without toxins<br />
<strong>Characteristics</strong> <strong>of</strong> <strong>the</strong> Scyphozoa<br />
stomach<br />
mouth<br />
mesoglea<br />
gastric pouch<br />
gonad<br />
radial canal<br />
gastrodermis<br />
Radial<br />
canal<br />
<strong>Characteristics</strong> <strong>of</strong> <strong>the</strong> Scyphozoa<br />
(Adaptations to a drifting, carnivorous lifestyle)<br />
G-V cavity more<br />
complex, adapted<br />
to subdue and<br />
digest larger and<br />
active prey<br />
Stomach<br />
G-V Canals<br />
MOUTH<br />
Gastric Pouches<br />
MANUBRIUM<br />
3
<strong>Characteristics</strong> <strong>of</strong> <strong>the</strong> Scyphozoa<br />
(Adaptations to a drifting, carnivorous lifestyle)<br />
Coronal<br />
Muscle<br />
and<br />
swimming<br />
G-V cavity more<br />
complex, adapted<br />
to subdue and<br />
digest larger and<br />
active prey<br />
How is swimming pace, direction coordinated?<br />
Associated with<br />
coronal muscles…<br />
Sensory neurons,<br />
motor neurons,<br />
Inner and outer<br />
nerve rings<br />
Marginal ganglia<br />
associated with<br />
rhopalia that<br />
constitute a<br />
pacemaker<br />
<strong>Characteristics</strong><br />
<strong>of</strong> <strong>the</strong> Scyphozoa<br />
(Adaptations to a drifting,<br />
carnivorous lifestyle)<br />
The nervous system<br />
is more complex;<br />
unique sensory<br />
structures<br />
Nerve net shared by<br />
all Cnidaria<br />
To ganglia<br />
4
Rhopalium<br />
24 eyes but no brain<br />
(Digestive)<br />
Marginal ganglia<br />
Inner and outer nerve rings<br />
Coronal muscles<br />
Nerve net<br />
Epiheliomuscular system<br />
Rhopalia are Intergrated with Nerve Rings<br />
Garm et al., 2006<br />
Cell Tissue Research #325<br />
When did a Centralized Nervous System Evolve?<br />
“Conventional” view<br />
Marlow et al., 2009, Developmental Neurobiology<br />
5
Cnidarian nerve net e.g. Hydra<br />
“Sub-functionalized” N.S.<br />
Sea Anemone Nematostella<br />
Nerve rings are Core <strong>of</strong> CNS in medusae<br />
-- Concentrations <strong>of</strong> hundreds <strong>of</strong> axons in parallel <strong>for</strong>m coupled nerve rings.<br />
Having an annular <strong>for</strong>m ra<strong>the</strong>r than a large ganglion does not make it<br />
less centralized.<br />
-- The annular configuration is a function <strong>of</strong> radial symmetry<br />
Mackie, 2004. Neurosignals #13<br />
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