Transcript Cnidaria_1_25_05

The three grades of metazoan animals
Animalia
KINGDOM:
GRADE:
Parazoa
PHYLA: Placozoa Porifera
Mesozoa
Mesozoa
Eumetazoa
All other
animal phyla
General Body Plan
•
Cellular level of
organization
•
Asymmetrical
•
Choanocytes
•
Mesohyl
spongin/ collagen
spicules
3 Body Types
Based on the complexity of the water canals:
• Asconoid
• Syconoid
• Leuconoid
Increasing size
Increasing Surface Area :Volume
The three grades of metazoan animals
Animalia
KINGDOM:
GRADE:
Parazoa
PHYLA: Placozoa Porifera
Mesozoa
Mesozoa
Eumetazoa
All other
animal phyla
Phylum Cnidaria
Level of Organization
Tissue
-similar cells are organized into tissues that work
together to accomplish a common function
-Cnidarians are diploblastic: they have 2 germ
layers
Tissue Layers
Diploblastic = 2 germ layers
• endoderm  gastrodermis (inner tissue)
• ectoderm  epidermis (outer tissue)
mesoglea
• gelatinous/ noncellular matrix between the 2
layers
Tissue Layers
epidermis
gastrovascular
cavity (GVC)
mesoglea
gastrodermis
Epidermal Cell types
Epitheliomuscular
cell
receptors
neurons
Epidermal Cell types
• cnidocytes: epidermal cells containing stinging
organelles (nematocysts). Unique to Cnidarians.
cnidocyte
Epidermal Cell types
Cnidocil: trigger
cnidocyte
Undischarged
Epidermal Cell types
neamtocyst
cnidocyte
discharged
Nematocysts
• nematocysts are like “mini-harpoons”
• cnidocil senses movement & acts like a “trigger”
• can inject poison, coil around prey, or be adhesive
• functions:
- prey capture; defense
nematocyst
cnidocil
cnidocyte
Undischarged
Discharged
Jellyfish sting
Gastrodermal Cell types
mesoglea
epidermis
gastrodermis
gland cells
nutritive-muscular
cells (ciliated)
General Body Plan
• sac-like body (only 1 opening)
oral surface
mouth
gastrodermis
mesoglea
Gastrovascular
cavity
epidermis
aboral surface
General Body Plan
Dimorphism: 2 different body forms are usually
present in the life cycle:
oral
aboral
aboral
oral
General Body Plan
- Radially symmetrical: body parts are arranged
concentrically around an oral-aboral axis
oral
aboral
General Life Cycle
Sexual
reproduction
Asexual
reproduction
Feeding and Digestion
Feeding
– nematocysts capture prey
– tentacles
Digestion
– extracellular (in GVC)
– intracellular (by gastrodermal cells)
– incomplete system (no anus)
Feeding and Digestion
•Food and waste go in/out the same opening
 no anus!
waste
Food
Feeding and Digestion
mesoglea gastrodermis
gland cells: secrete mucus,
entraps food particles
nutritive-muscular cells:
create water currents,
circulate food particles in
GVC
epidermis
Nervous System
– nerve net
(no central nervous system= no brain)
receptors
nerve net
neurons
Nervous System
– sense organs
– statocysts (equilibrium cells)
– ocelli (photosensitive cells)
Nervous System
ocelli
statocysts
Skeletal Support
– water in GVC acts as a hydrostatic skeleton
Muscles act
against water
trapped in the
GVC
Skeletal Support
•water within GVC acts as a hydrostatic
skeleton:
Skeletal Support
Reproduction
Asexual
– pedal laceration
(e.g. sea anemones)
Reproduction
Asexual
– budding
Buds
Reproduction
Asexual
– longitudinal fission
Reproduction
Sexual
– usually dioecious
(separate sexes)
– monoecious
(both male + female gonads in 1 individual)
– results in Planula larva
Phylum Cnidaria
Three Classes:
Class Hydrozoa
Class Scyphozoa
Class Anthozoa
These classes differ
in the prominence of
the polyp and
medusa stages
Class Hydrozoa
• medusa & polyp body forms
Fire coral
Class Hydrozoa
• medusa & polyp body forms
• most are colonial
 colonies are formed of
individuals (zooids)
a single zooid
Class Hydrozoa
• many of these colonies are polymorphic
 there are several different types of polyps/zooid and
each type is specialized for a different function
 all the zooids within a colony are genetically identical
and are connected by a common GVC
Class Hydrozoa
- a sessile colony showing polymorphism
gonozooid
GVC
entire
colony
gastrozooid
Class Hydrozoa
- a Portugese Man-o-war is a floating hydrozoan
colony showing polymorphism
pneumatophore
entire
colony
gastrozooid
dactylzooid
Class Hydrozoa- life cycle
sexual
reproduction
asexual
reproduction
Class Hydrozoa
• Hydra is an example of a solitary, freshwater hydrozoan
asexual
reproduction
sexual
reproduction
gonads
bud
Class Scyphozoa
• “true” jellyfish
• medusa & polyp body forms
• thick mesoglea
Class Scyphozoa- life cycle
adult medusa
sperm and egg
larva
ephyra
scyphistoma
strobila
Class Anthozoa
• polyp body form ONLY
• all marine
Class Anthozoa
• some are colonial
 colonies are formed of individual
zooids (e.g. corals)
• some are solitary
(e.g. anemones)
Class Anthozoa
Sea anemones
Class Anthozoa
Soft Corals
Sea pen
Sea pansy
Class Anthozoa
Stony Corals
Class Anthozoa- life cycle
Sexual reproduction
sperm egg
larva
Class Anthozoa- life cycle
asexual reproduction
fission
pedal laceration
fission
Colony formation
• colony formation is common (colonial animals)
• occurs via asexual reproduction (e.g. fission)
• individual polyps are connected to one another by a
common GVC
individual polyp
Symbiosis
Mutualism –
• Corals contain endosymbiotic algae called
zooxanthellae
• the zooxanthellae photosynthesize and provide food for
the coral while the coral provides a safe home
zooxanthellae
Coral Reefs
What are they?
• stony corals lay down a calcium carbonate
skeleton
• these skeletons are laid down on top of one
another and over thousands of years, form
large calcium carbonate structures
• these large structures, along with the plants and
animals that inhabit them, are known as coral
reefs
Distribution of Coral Reefs
Coral Species Diversity
Number of coral species
increases with decreasing
depth:
• increasing illumination
•Increasing radiant energy
Distribution of Coral Reefs
Habitat requirements
1. High light
2. Clear water
3. Water temp: 20 0 – 28 0 C
Required for
zooxanthellae
Importance of Coral Reefs
• one of the most productive ecosystems although
the water is nutrient-poor
• “hot spots” for biodiversity
Threats to Coral Reefs
• over-enrichment of nutrients from sewage and
agricultural run-off
• overfishing of herbivorous fish
• global warming (leads to coral bleaching where
corals expel their zooxanthellae)
Coral
bleaching
FSU Research on Cnidarians: Dr. Don Levitan
[email protected]
Reproductive isolation in
broadcast-spawning marine
invertebrates.
Biological species concept: a species is a
population or group of populations that can
potentially interbreed and produce viable,fertile
offspring, but that is reproductively isolated from
other populations.
Western meadowlark
Eastern meadowlark
How do species of broadcast-spawning marine
invertebrates remain reproductively isolated
from one another?
The Montastrea annularis species complex
1. Montastrea annularis
2. Montastrea faveolata
3. Montastrea franksi
M. annularis
M. franksi
M. faveolata
Gamete bundles:
contain sperm and
eggs
Gamete bundles are released
and float to the surface. At the
surface, sperm an eggs are
released.
The Montastrea annularis species complex
1. Montastrea annularis
2. Montastrea faveolata
3. Montastrea franksi
All three species are
sympatric, and spawn ~
8 days after a full moon
in late summer
Lee Stocking Island
Curacao
Bocas del Toro
San Blas
How do species of broadcast-spawning marine
invertebrates remain reproductively isolated
from one another?
1. Time of spawning
Do species spawn at the same time
after sunset?
Do species spawn at the
same time after sunset?
M. franksi spawns earlier than both
M. faveolata and M. annularis
Levitan et al. 2004
2. Gametic compatibility experiments
Are gametes from different species
compatible?
egg
M. an
M. an
M. fr
M. fav
M. fr
M. fav
Measure
fertilization
success
M. franksi x M. annularis
M. faveolata x M. annularis
Bahamas
M. faveolata x M. franksi
A
104
80
A
AB
8
60
C
21
C
6
C
17
v
k
40
20
93
B
70
a
Percent Fertilization
100
C
89
C
34
C
33
C
32
C
33
Cross type
Levitan et al. 2004
vs ke
ks ve
as ve
vs ae
ks ae
as ke
kk
vv
aa
0
How do species of broadcast-spawning marine
invertebrates remain reproductively isolated
from one another?
The Montastrea annularis species complex
Spawn
simultaneously
Spawns earlier
than the other 2
1. Montastrea annularis
2. Montastrea faveolata
3. Montastrea franksi
Gametes
incompatible
Gametic
compatibility with
M. annularis,
incompatible with
M. faveolata
How do species of broadcast-spawning marine
invertebrates remain reproductively isolated
from one another?
•In the M. annularis species complex, reproductive
isolation is due to a combination of:
1. Temporal isolation
2. Gametic isolation
3. Spatial isolation- depth
•None of these mechanisms is completely effective on
its own, but together they result in isolation