Download Outline 6: Cnidaria 1

Invertebrate Zoology
Lecture 6: Phylum Cnidaria, Part 1 (FIXED AND FINAL VERSION!)
Lecture outline (summary)
I.
Overview
II.
Overall body structure
A.
Body wall
B.
Cnidocytes
III.
Bauplan, polyp (Anthozoa)
IV.
Bauplans, medusae
A.
Hydrozoa
B.
Scyphozoa
C.
Cubozoa
D.
Focus on nervous systems/sensory structures
I.
Overview
A.
Thought to be plants until 18th century
B.
Two basic body forms  diverse array of organisms
C.
Four classes
1.
Class Hydrozoa (clockwise from top)
a)
Hydroids
b)
Hydromedusae
c)
by-the-wind sailors
d)
Siphonophores
2.
Class Scyphozoa
a)
Large jellies
b)
Stauromedusae
3.
Class Cubozoa
a)
Box jellies
4.
Class Anthozoa
a)
Anemones
b)
Coral
c)
Sea pansies
d)
Gorgonians
D.
Evolutionary relationships (briefly)
1.
Thought to have arisen relatively early in animal evolution—one of the longest
fossil histories
2.
Key derived characters
a)
diploblasty
b)
radial symmetry
3.
Was the first cnidarian a polyp or a medusa?
E.
Key characteristics (see Box 8A)
1.
Diploblastic; epidermis & endodermis
2.
Mesoglia/mesenchyme between tissue layers
3.
Radial symmetry (may be biradial, etc…)
4.
Possess cnidocytes
5.
“Muscles” associated with epidermis, endodermis
6.
Many alternate between asexual polyps and sexual medusae
7.
Contain gastrovascular cavity, not a true body cavity
8.
No head; no special body systems for circulation, gas exchange or excretion.
9.
Nervous system is a nerve net
10.
Have planula larvae
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II.
III.
Overall body structure
A.
Body wall
1.
Epidermis
a)
Epitheliomuscular cells:

Contractile portion at base (=myoneme)
b)
Epidermal gland cells
c)
Sensory cells
d)
Nerve cells
e)
Cnidocytes
2.
Gastrodermis
a)
Nutritive-muscular cells

Contractile portion at base (=myoneme)
b)
Enzymatic gland cells
c)
Mucus gland cells
d)
Nerve cells
e)
Cnidocytes
3.
Mesoglia/mesenchyme
a)
Between the epidermis and gastrodermis
b)
Mesoglia vs. mesenchyme
c)
Thicker in medusae than polyps
B.
Cnidocytes
1.
Functions
2.
Cnidae
3.
Focus: nematocyst-bearing cnidocyte
a)
Cell body
b)
Cnidocil: how triggered?
c)
Operculum
d)
Nematocyst capsule

With toxins
e)
Shaft
f)
Stylets and spines (Function?)
g)
Hollow filament (Function?)
4.
Cnidocyte: firing
a)
Trigger cnidocil
b)
Eversion of shaft and filament
c)
Injection of toxins
5.
Hypotheses
a)
Osmotic hypothesis
b)
Tension hypothesis
c)
Contractile hypothesis
6.
Other cnidae (adhesive)
a)
Spirocysts
b)
Ptychocysts (no image)
Bauplan, polyps (Anthozoa)
A.
Tentacles
1.
Not true appendages (why not)
2.
Contain branches of the g.v. cavity
3.
Epidermal layer with cnidocytes
4.
Acrorhagi: specialized defensive tentacles
B.
Oral disc/ mouth/ pharynx
1.
Epidermis extends down pharynx (NOTE: Hydrozoan polyps lack a pharynx)
C.
Siphonoglyph
1.
Ciliated grooves: create water current (often have two)
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IV.
2.
Water flow pattern?
3.
Reversal of flow?
D.
Gastrovascular cavity
1.
Functions
2.
Movement into g.v. cavity
3.
Movement within g.v. cavity: What causes fluids to circulate?
4.
Mesenteries
a)
Folds of gastrodermis
b)
Divide the g.v. cavity

Function?

Some complete, others not
c)
Cnidocytes associated with mesenteric filaments.

Acontia: Free-hanging filaments; defensive
d)
Gonads associated with mesenteries (Anthozoa)
e)
Myonemes
E.
Column/Pedal disc
1.
Attachment
a)
Epidermal gland cells
2.
Movement
a)
Why move?
b)
Sessile polyps
c)
Burrowing anemones

Peristalsis
F.
Nervous system/sensory structures
1.
Mostly non-polar nerve cells
a)
Bi-directional AP
b)
Two-way synapses
2.
No distinct dendrites
3.
No ganglia or nerve cords
4.
Nerve nets (2 arrays)
5.
Polyps have minimal sensory structures
a)
Mechanoreceptive hairs (also chemoreceptive?)
b)
Ciliary cones (assoc. with cnidocytes)
c)
Response to light
Bauplan, medusae
A.
Class Hydrozoa (Hydromedusae)
1.
Exumbrella
2.
Subumbrella
3.
Thick mesoglia
a)
Elastic, aids in movement
4.
Velum
a)
Directs water jet
b)
Increases water velocity
5.
Ring of tentacles
a)
hollow, lined with gastrodermis
6.
Manubrium
a)
Mouth & pharynx-like tube
7.
Gastrovascular cavity
a)
Four radial canals
b)
ring canal
c)
Tentacles
d)
Digestion, etc… similar to polyps
e)
No cnidocytes in g.v. cavity
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8.
B.
C.
D.
Gonads outside of radial canals
a)
sexes separate
Class Scyphozoa (Scyphomedusae)
1.
No velum
2.
Mouth lobes with cnidocytes
a)
Manubrium reduced or absent
3.
Gastrovascular cavity
a)
radial canals highly branched
b)
Have cnidocytes in g.v. cavity
c)
gastric filament: secretes enzymes

More effective extracellular digestion
d)
gonads within g.v. cavity

sexes separate
Class Cubozoa (Cubomedusae)
1.
Differences from hydromedusae
a)
Gonads are within the g.v. cavity
b)
Gastric filaments are present
2.
Obvious quadriradiate symmetry
Nervous system/sensory structures (medusae)
1.
Hydromedusae
a)
Nerve net
b)
Nerve rings (function?)
c)
Statocysts (in some)
d)
General sensory cells
e)
Ocelli
2.
Scyphomedusae
a)
Nerve net
b)
No nerve rings (usually)
c)
Rhopalia:

Lower edge of bell

Include Statocysts, chemosensory pits and ocelli
3.
Cubomedusae
a)
Rhopalia
b)
Up to 24 eyes

Cornea, lens and retina!
c)
Up to 11,000 sensory cells per eye

Integration?

Images?
d)
Function
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