Transcript PowerPoint 6: Cnidaria 1

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