1. 1

2.  A metazoan
 Lineage ~700MY old
 Named after cindocytes –
stinging cells
 Most common type - nematocyst
 Body plan simple, sac-like
 Symmetry is radial or biradial
 Aquatic - mostly marine, some
freshwater species
 Show tissue level of organization
2

3.  Symmetry – radial
 No “head”
 Has oral & aboral ends
 Polymorphism present
 Polyp (sessile) & medusa (free-swimming) body
types
 Gastrovascular cavity
 single opening (mouth/anus) surrounded by
tentacles
 H2O within serves as hydrostatic skeleton
3

4.  Stinging cell organelles, cnidae, prevalent on tentacles,
epidermis, &/or gastrodermis
 Nematocysts most abundant type
 Nerve net present, some sensory organs
 Statocysts – balance organs
 Ocelli – simple light sensors
 Muscle fibers present
 Reproduction
 Asexual: budding (polyp)
 Sexual: planula larvae (medusa, some polyp forms)
 Individuals may be monoecious or dioecious
 No excretory or respiratory systems; diffusion suffices
4

5. 5
Pedal Disc
Aboral End 
Oral End 
Oral End 
Aboral End 
Mouth & anus are the same opening
Digestion extracellular in gastrovascular cavity; smaller particles
ingested intracellularly

6.  Food source for mollusks & fish
 Some ctenophores, mollusks, & flatworms will
eat hydroids w/ nematocysts
 Habitats:
 Coral reefs home to fish, arthropods
 Hydroids attach to underwater structures
 Commensalism on mollusk shells
 Aquatic organisms provide food source for
cnidarians
 Rarely provide food for human
consumption
6

7. Polyp: hydroid form;
sessile; aboral end
attached to substrate by
pedal disc
Medusa: umbrella
shaped; free-swimming
Body tubular; mouth
upward ringed by
tentacles
Body sac-like; mouth
downward; tentacles
ring umbrella
Asexual reproduction:
budding, fission, pedal
laceration
Sexual reproduction
occurs too
Reproduction sexual
&/or asexual
Medusa usually
dioecious
Sea anemones & corals
are polyps – no medusa
stage
Includes Scyphozoans
& Cubozoans
Locomotion: Hydras
move freely, polyps
sessile, sea anemones
move on basal disc
Locomotion: medusa
move freely about, at
mercy of waves
7

8.  Cnidarians mostly voracious carnivores,
but predatory capabilities hampered by
body plan.
 Polyps rely on stinging cells to
capture/paralyze any organism the tide
brings by
 Medusa rely on stinging cells to do same
even though they are free-swimming
(realize inability to totally control where they swim)
8

9. 9
Stinging cells triggered
by mechanical or
chemical stimuli

10. 10

11.  Cell generates osmotic pressure up to 140
atm that causes the ejection to occur
 Hydrostatic pressure increases as osmotic
pressure decreases
 Due to high osmotic pressure, stimulus
causes H2O to rush in opening operculum
11

12.  High hydrostatic pressure launches the
thread within 3 milliseconds with an
acceleration power of 40,000 g and a
penetration force of 20-33 kPa; barbs
point rear & anchor in victim’s tissue;
poison injected
 Nematocysts are capable of penetrating
up to a depth of 0.9 mm
 Lost nematocyst must be replaced
12

13.  While the amount of toxin expressed by a single
nematocyst is minute, several thousand
nematocysts discharging at once have a
significant effect.
 Functionally, the toxin causes Na+ and Ca++ ion
transport abnormalities, disrupts cellular
membranes, releases inflammatory mediators,
and acts as a direct toxin on the myocardium,
nervous tissue, hepatic tissue, and kidneys.
13

14.  Specifically, the toxin may contain
catecholamines, vasoactive amines (eg,
histamine, serotonin), kinins,
collagenases, hyaluronidases, proteases,
phospholipases, fibrinolysins,
dermatoneurotoxins, cardiotoxins,
neurotoxins, nephrotoxins, myotoxins,
and antigenic proteins. The protein
component of the toxin tends to be heat
labile, nondialyzable, and is degradable
by proteolytic agents.
14

15.  United States
 Jellyfish stings occur most commonly during the summer along
coastal regions. As the coastal population grows and more tourists
come to the beaches, the frequency of jellyfish sting is likely to
increase. One investigator reported 500,000 annual
envenomations in the Chesapeake Bay area and 200,000 annually
along the Florida coast.
 International
 Jellyfish stings occur in tropical oceans, especially between
latitudes 30° south to 45° north, because of a high natural
concentration of cnidarians. This is especially true of the east
coast of Australia during the warm summer months between
November and May. (Don’t forget, they’re in the southern
hemisphere, so their summer is during our winter)
15

16.  Jellyfish stings usually are mild, except those
caused by species in the South Pacific, such as
the box jellyfish or Portuguese man-of-war.
Exact mortality and morbidity is not known
because of underreporting and the lack of an
international jellyfish sting registry.
 However, a recent epidemiology study of 118
cases of jellyfish stings from the Texas gulf coast
showed 0.8% had no effect, 80.5% had minor
effects, and 18.6% had moderate effects.
16

17.  Box jellyfish venom has a median lethal dose of
40 mcg/kg, which makes it the most potent
marine toxin. The venom may kill a person
weighing 70 kg within 3 minutes and is
responsible for a mortality rate of 20%.
 Box jellyfish venom has caused 72 deaths
secondary to respiratory paralysis,
neuromuscular paralysis drowning, and
cardiovascular collapse.
17

18.  The pain and spasms spread centrally as the
venom travels to the central circulatory
system, inducing parasympathetic
overstimulation and respiratory-cardiac
arrest.
 Most fatalities occur within 20 minutes of the
envenomation; according to animal studies,
approximately 5-10 mcg/kg of venom is
required to induce cardiac arrest.
18

19.  The sting of the Portuguese man-of-war is
more painful than a common jellyfish
sting. It has been described as feeling like
being struck by a lightning bolt, and some
victims dread it more than a shark bite.
This sting has been responsible for 2
reported deaths.
19

20.  The Arctic jellyfish is the largest, with tentacles
reaching 200 ft, allowing the jellyfish to sweep
an area slightly larger than a basketball court.
20

21.  Contains 2 nerve nets at base of
epidermis and gastrodermis which
connect
 Nerve impulses carried by
neurotransmitters via snapses
 Transmission can go either direction
 Lack myelin sheath around axons
 No brain, no centralized nervous system
 Sense organs simple
 Statocysts & Ocelli
21

22.  The statocyst is a balance organ present in
some aquatic invertebrates
(Cnidarians,Ctenophores, Bilaterians). It
consists of a sac-like structure containing a
mineralized mass (statolith) and numerous
innervated sensory hairs (setae).
 The statolith possesses inertia, causing the mass
to move when accelerated. Deflection of setae
by the statolith in response to gravity activates
neurons, providing feedback to the animal on
change in orientation and allowing balance to be
maintained.
 Because organism has no “brain,” they are
limited in their actions and responses to stimuli.
The statocyst is therefore useful for telling the
animal whether it is upside down or not.
22

23.  The phylum Cnidaria includes the first multicellular
animals to form eyes; this group exhibits a diversity
of eye designs ranging from a simple photosensitive
sheet of cells to the complex image forming eyes of
cubozoan jellyfish.
 Because of their basal position on the phylogenetic
tree, cnidarians provide an excellent system in which
to study the evolution of the first multicellular animal
eyes and the evolution of photosensory mechanisms.
23

24.  The camera-type eyes of cubozoans represent the
most highly evolved eyes in the Cnidaria.
 Further they contain the visual pigments involved
in phototransduction: rhodopsin and opsins.
 These eyes resemble the proposed ancestral
prototype eye.
24

25.  Class Hydrozoa:
 Marine & freshwater, colonial, polyp & medusa
forms
 Class Scyphozoa
 Marine, most medusa forms
 Class Cubozoa
 Marine, medusa form prominent, no known
polyp forms, toxin lethal to humans
 Class Anthozoa
 Marine, polyps only, no medusa form
25

26.  Hydra & Obelia are good
examples of this class
 Hydra:
 Freshwater species, 16 in N. America
 Solitary polyps (typical form)
 Eat larvae, worms, crustaceans
 Asexual rep – budding;
 Sexual Rep – prod of sperm/ova
 Overwinter as cysts
26

27.  Colony has base, stalk, & terminal polyps
(zooids)
 Gastrozooids (feeding)
 Gonophores (reproduction)
 Dactylozooids (defense, tentacles)
 Eat crustaceans, worms, larvae
 Buds remain attached, incr colony size
 Medusa produced by asex. Budding, released
 Medusa – dioecious, reprod sexually
 Planula larva attach, forming new colony
27

28. 28

29. 29

30.  Most “jellyfish” belong here
 Medusa body form
 Marine, free-swimming
(mostly), open sea
 Aurelia example of
scyphozoan
 Dioecious, fertilization
internal, planula zygote
 Zygote develops, forms buds
(asexually) which produce
new medusa
30

31.  Box “jellyfish”
 Note prominent “eyes”
 Medusa dom body form
 Polyp form unknown
 Strong swimmers, good
hunters
 Toxic venom
31

32. 32
Pedalium: flat
blade at base of
each tentacle
(see arrow)


33.  Sea anemones & coral found in this class;
another is sea pens
 Medusa body form not seen
 All are marine, shallow water dwellers
33

34.  Polyps large, heavy
 Attach to substrate via pedal discs, may
burrow in sand/mud/silt
 Tentacles ring the oral opening; mouth/anus
slit shaped
 Reproduction: Sexual or asexual
 Monoecious & dioecious individuals
 Gonads internal; fertilization external
 Zygote becomes a ciliated larva
 Budding, pedal laceration, & fission may
produce new individual asexually
34

35. 35
Bonaire Giant
Anemone 
Note fluorescence

36. 36
Clown fish 
Pink Anemone Fish
Commensal
relationships between
fish & anemone
 Saddleback Clownfish

37.  Two types of corals:
 Zoantharian corals – true or stony
corals
 Octocorallian corals – soft corals,
colonial
 Both form coral reefs
 structures produced by living
organisms. In most reefs the
predominant organisms are colonial
cnidarians that secrete an exoskeleton
of calcium carbonate. The
accumulation of this skeletal material,
broken and piled up by wave action and
bioeroders, produces massive
calcareous formations that make ideal
habitats for living corals and a great
variety of other animal and plant life.
37
Brain Coral

38.  Coral reefs are estimated to cover 284,300
km2, with the Indo-Pacific region (including
the Red Sea, Indian Ocean, Southeast Asia and
the Pacific) accounting for 91.9% of the total.
Southeast Asia accounts for 32.3% of that
figure, while the Pacific including Australia
accounts for 40.8%. Atlantic and Carribean
coral reefs only account for 7.6% of the world
total.
38

39.  The Great Barrier Reef - largest coral reef system in the
world, Queensland, Australia;
 The Belize Barrier Reef - second largest in the world,
stretching from southern Quintana Roo, Mexico and all
along the coast of Belize down to the Bay Islands of
Honduras.
 The New Caledonia Barrier Reef - second longest double
barrier reef in the world, with a length of about 1500km.
 The Andros, Bahamas Barrier Reef - third largest in the
world, following along the east coast of Andros Island,
Bahamas between Andros and Nassau.
 The Red Sea Coral Reef - located off the coast of Israel,
Egypt and Saudi Arabia.
 Pulley Ridge - deepest photosynthetic coral reef, Florida
39

40.  The coral polyps do not photosynthesize, but have a
symbiotic relationship with single-celled algae
called zooanthellae
 these algal cells within the tissues of the coral
polyps carry out photosynthesis and produce excess
organic nutrients that are then used by the coral
polyps.
 Because of this relationship, coral reefs grow much
faster in clear water, which admits more sunlight.
Indeed, the relationship is responsible for coral
reefs in the sense that without their symbionts,
coral growth would be too slow for the corals to
form impressive reef structures.
 Corals can get up to 90% of their nutrients from
their zooxanthellae symbionts. 40

41. 41
Star Coral
Elkhorn Coral
Fluorescent
Coral

42.  Coral reefs support an extraordinary biodiversity;
although they are located in nutrient-poor tropical
waters.
 The process of nutrient cycling between corals,
zooanthellae, and other reef organisms provides
an explanation for why coral reefs flourish in
these waters: recycling ensures that fewer
nutrients are needed overall to support the
community.
 Cyanobacteria also provide soluble nitrates for the
coral reef through the process of nitrogen oxigen.
Corals absorb nutrients, including inorganic
nitrogen and phosporus, directly from the water,
and they feed upon zooplankton that are carried
past the polyps by water motion. 42

43.  Thus, primary productivity on a coral reef
is very high, which results in the highest
biomass per square meter, at 5-10g C m-2
day-1.
 Producers in coral reef communities
include the symbiotic zooxanthellae,
sponges, marine worms, seaweed, coralline
algae(especially small types called turf
algae.
43

44. 44
Red Stalk Jellyfish
Portuguese Man-o-War
This scyphozoan is
unusual; it is attached
not free floating

45. 45
Note: Large float in this species
Velella &
Man-o-war
are only
scyphozoans
with floats

46. 46
Orange Sea Pen

47. 47
Arctic Jellyfish
Sea Fan

48.  x
48
Jellyfish washed ashore

49.  Marine, prefer warmer H2O
 About 100 species known
 Size range: few mm to 1.5m
 Medusa contains 8 rows of
fused cilia plates for
locomotion
 Some bioluminescent
 Have 2 tentacles; only 1
species known to have
nematocysts
49

50.  Comb plates extend from
aboral to oral end
 Fused cilia along plate which
beat from aboral to oral ends
 All plates beat in unison,
moving food toward mouth
 Two tentacles; long &
retractable
 Surface bearing colloblasts
which are sticky
50

51. No central nervous system
 Statocysts present for balance
 Sensory cells in epidermis
Individuals are monoecious
 Fertilization external
Some brood eggs
 Larva free swimming
51

52. 52

53. 53
“Tortugas Red”
Comb Jelly
Benthic
Ctenophoran
