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Hydras, jellyfish, sea anemones, and corals
belong to the phylum Cnidaria.
these diverse animals are all armed with
stinging cells called nematocysts
The name Cnidaria comes from the Greek
word "cnidos," which means stinging nettle.
Casually touching many cnidarians will make
it clear how they got their name when their
nematocysts eject barbed threads tipped with
poison.
 Cnidarians have two basic body forms, and
both show radial symmetry.
 Medusa forms are free-floating, jellylike, and
often umbrella-shaped.
 Polyp forms are tube like and are usually
attached to a rock or some other object.
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Polymorphic- alternates between polyp and
medusa
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1. Radial symmetry is primary
2. Gastrovascular cavity for digestion
3. Tentacles - feeding, locomotion, defense
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Reproduction in polyps is by asexual budding
(polyps) or sexual formation of gametes
(medusae, some polyps). Cnidarian
individuals may be monoecious or dioecious.
The result of sexual reproduction is a planula
larva, which is ciliated and free-swimming.
• Embryo --> planula --> polyp or
medusa
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Class hydrozoa- hydra, fire coral, Portuguese
man-of-war
Class scyphozoa- jelly fish
Class cubozoa- box jellies
Class Anthozoa-anemones, corals
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2700 species of hydras, colonial hydroids,
fire corals
polyp, medusa, polymorphic
Freshwater Hydrozoa
 Hydras live in quiet ponds, lakes, and
streams.
 They attach to rocks or water plants by
means of a sticky secretion they produce in
an area of their body called the basal disk
 Marine hydrozoans are typically far more
complex than freshwater hydrozoans.
 Often many individuals live together, forming
colonies
 Most hydrozoans are colonial organisms
whose polyps reproduce asexually by forming
small buds on the body wall. Many
hydrozoans are also capable of sexual
reproduction.
 During sexual reproduction, the medusas
release sperm or eggs into the water.
 The gametes fuse and produce zygotes that
develop into free-swimming, ciliated larvae
called planulae.
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Hydra mainly feed on small aquatic
invertebrates such as Daphnia and Cyclops
(water flea).
When feeding, Hydra extend their body to
maximum length and then slowly extend
their tentacles. Despite their simple
construction, the tentacles of Hydra are
extraordinarily extensible and can be four to
five times the length of the body
a.
Epidermis
 interstitial cells - capable of forming
other tissues
 nerve cells - sensory and motor
 cnidocytes - discharge nematocysts,
used once
b. Mesoglea
 jelly-like matrix, mostly acellular, fluid
or rigid
c. Gastrodermis
 nutritive-muscle and enzymatic cells
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Hydra dance video
Hydra eating video
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Despite its outward appearance, the man o'
war is not a jellyfish but a siphonophore,
which differs from jellyfish in that it is not
actually a single organism, but a colonial
organism made up of many minute
individuals called zooids.
they are attached to one another and
physiologically integrated to the extent that
they are incapable of independent survival
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The Portuguese man o' war lives at the
surface of the ocean. The gas-filled bladder,
or pneumatophore, remains at the surface,
while the remainder is submerged.Since the
man o' war has no means of propulsion, it is
moved by a combination of winds, currents,
and tides
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It is composed of four types of polyp. One of
the polyps, a gas-filled bladder called the
pneumatophore (commonly known as the
sail), enables the organism to float. This sail
is bilaterally symmetrical, with the tentacles
at one end, and is translucent, tinged blue,
purple, pink, or mauve. It may be 9 to 30
centimetres (3.5 to 12 in) long and may
extend as much as 15 centimetres (5.9 in)
above the water.
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The other three polyp types are known as
dactylozooid (defence), gonozooid
(reproduction), and gastrozooid
(feeding).These polyps are clustered. The
dactylzooids make up the tentacles that are
typically 10 metres (33 ft) in length but can
be up to 50 metres (160 ft
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The Portuguese man o' war is a carnivore.
Using its venomous tentacles, a man o' war
traps and paralyzes its prey. Typically, men o'
war feed upon small aquatic organisms, such
as fish and plankton.
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The loggerhead turtle feeds on the Portuguese
man o' war, a common part of the loggerhead's
diet.The turtle's skin is too thick for the sting to
penetrate.
The sea slug Glaucus atlanticus also feeds on the
Portuguese man o' war,as does the violet snail
Janthina janthina.
The blanket octopus is immune to the venom of
the Portuguese man o' war; young individuals
carry broken man o' war tentacles, presumably
for offensive and/or defensive purposes
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Fire corals are colonial marine organisms that
look rather like real coral.
Fire corals have a bright yellow-green and
brown skeletal covering and are widely
distributed in tropical and subtropical waters.
They appear in small brush-like growths on
rocks and coral.
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Divers often mistake fire coral for seaweed,
and accidental contact is common. Upon
contact, an intense pain can be felt that can
last from two days to two weeks
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Fire coral has several common growth forms,
these include:
branching
Plate
encrusting
 Branching
adopts
a calcareous
structure which
branches off, to
rounded fingerlike tips
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Plate adopts a shape
similar to that of the
smaller non-sheet
lettuce corals;
therefore erect, thin
sheets, which group
together to form a
colony
encrusting, is
where the fire
coral forms on
the calcareous
structure of
other coral
Encrusting
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The polyps of fire corals are near microscopic
size and are mostly embedded in the skeleton
and connected by a network of minute canals.
All that is visible on the smooth surface are
pores of two sizes: gastropores and
dactylopores
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Dactylopores have long fine hairs that
protrude from the skeleton. The hairs
possess clusters of stinging cells and capture
prey, which is then engulfed by gastrozooids,
or feeding polyps, situated within the
gastropores
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Reproduction in fire corals is more complex
than in other reef-building corals. The polyps
reproduce asexually, producing jellyfish-like
medusae, which are released into the water
from special cup-like structures known as
ampullae.
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The medusae contain the reproductive organs
that release eggs and sperm into the water.
Fertilized eggs develop into free-swimming
larvae that will eventually settle on the
substrate and form new colonies. Fire corals
can also reproduce asexually by
fragmentation
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Medusa form
They are classified as free-swimming marine
animals consisting of a gelatinous umbrellashaped bell and trailing tentacles
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Most jellyfish do not have specialized
digestive, central nervous, respiratory, or
circulatory systems.
The manubrium is a stalk-like structure
hanging down from the center of the
underside, with the mouth at its tip.
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The manubrim opens into the gastrovascular
cavity, where digestion takes place and
nutrients are absorbed.
It is joined to the radial canals which extend
to the margin of the bell.
Jellyfish do not need a respiratory system
since their skin is thin enough that the body
is oxygenated by diffusion.
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They have limited control over movement,
but can use their hydrostatic skeleton to
navigate through contraction-pulsations of
the bell-like body; some species actively
swim most of the time, while others are
mostly passive.
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Depending on the species, the body contains
between 95 and 98% water.
Most of the umbrella mass is a gelatinous
material (the jelly)called mesoglea which is
surrounded by two layers of protective skin.
The top layer is called the epidermis, and the
inner layer is referred to as gastrodermis,
which lines the gut.
Development
The developmental
stages of
scyphozoan
jellyfish's life
cycle:
1–3 Larva searches
for site
4–8 Polyp grows
9–11 Polyp
12–14 Medusa
grows
Jellyfish reproduce both
sexually and asexually
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jellyfish spawn daily given enough food. In
most species, spawning is controlled by light,
so the entire population spawns at about the
same time of day, (either dusk or dawn).
Jellyfish are usually either male or female In
most cases, adults release sperm and eggs
into the surrounding water, where the
(unprotected) eggs are fertilized and mature
into new organisms.
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After a growth interval, the polyp begins
reproducing asexually by budding.
Budding sites vary by species; from the
tentacle bulbs, the manubrium (above the
mouth), or the gonads of hydromedusae
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Jellyfish lifespans typically range from a few
hours to several months.
Life generally ends after the medusa has
begun spawning. Life span varies by species.
Most large coastal jellyfish live 2 to 6 months,
during which they grow from a millimeter or
two to many centimeters in diameter.
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Jellies are carnivorous, feeding on plankton,
crustaceans, fish eggs, small fish and other
jellyfish, ingesting and voiding through the
same hole in the middle of the bell.
Jellies hunt passively using their tentacles as
drift nets
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Contact with a jellyfish tentacle can trigger
millions of nematocysts to pierce the skin and
inject venom.
Touching or being touched by a jellyfish can
be very uncomfortable, sometimes requiring
medical assistance; sting effects range from
no effect to extreme pain to death.
Even beached and dying jellyfish can still
sting when touched.
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distinguished by their cube-shaped medusae
The underside of the umbrella includes a flap,
or velarium, concentrating and increasing the
flow of water expelled from the umbrella.
As a result, box jellyfish can move more
rapidly than other jellyfish.
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are known for the extremely potent venom
produced by some species.
Chironex fleckeri, Carukia barnesi and Malo
kingi are among the most venomous
creatures in the world
. Stings from these and a few other species in
the class are extremely painful and
sometimes fatal to humans.
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The box jellyfish actively hunts its prey
(zooplankton and small fish), rather than
drifting as do true jellyfish.
Each tentacle has about 500,000 cnidocytes,
containing nematocysts, a harpoon-shaped
microscopic mechanism that injects venom
into the victim. Many different kinds of
nematocysts are found in cubozoans
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Although the box jellyfish has been called
"the world's most venomous creature",only a
few species in the class have been confirmed
to be involved in human deaths, and some
species pose no serious threat at all.
In Australia, fatalities are most
often perpetrated by the largest
species of this class of jellyfish
Chironex fleckeri.
Corals
Sea Anemone
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Largest class
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Only exist as polyps
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They retain their nematocysts, or stinging
cells, and may feed on large prey or
particulate food, a number of them
supplement their diet by growing symbiotic
algae in their tissues
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polyp attached at the bottom to the surface
beneath it by an adhesive foot, called a basal
disc, with a column-shaped body ending in
an oral disc.
Most are from 1.8 to 3 centimeters in
diameter, but anemones as small as 4
millimeters or as large as nearly 2 meters are
known.
They can have anywhere from a few tens to a
few hundred tentacles
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The mouth, also the anus of the sea
anemone, is in the middle of the oral disc
surrounded by tentacles armed.
The venom is a mix of toxins, including
neurotoxins, that paralyzes the prey so the
anemone can move it to the mouth for
digestion inside the gastrovascular cavity.
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Both sexual and asexual reproduction can
occur.
In sexual reproduction males release sperm
to stimulate females to release eggs, and
fertilization occurs. Anemones eject eggs and
sperm through the mouth. The fertilized egg
develops into a planula, which settles and
grows into a single polyp.
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Anemones can also reproduce asexually, by
budding, binary fission (the polyp separates
into two halves), and pedal laceration, in
which small pieces of the pedal disc break off
and regenerate into small anemones.
 Most coral polyps live in colonies called reefs.
 Each polyp secretes a tough, stonelike outer
skeleton of calcium carbonate that is
cemented to the skeletons of its neighbors.
 Over thousands of years, these formations
build up into coral reefs where hundreds of
thousands of polyps live together on top of
old skeletons.
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Although some corals can catch small fish
and plankton, using stinging cells on their
tentacles, like those in sea anemone and
jellyfish, most corals obtain the majority of
their energy and nutrients from
photosynthetic unicellular algae that live
within the coral's tissue called zooxanthella
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The polyps interconnect by a complex and
well-developed system of gastrovascular
canals, allowing significant sharing of
nutrients and symbiotes.
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Corals predominantly reproduce sexually.
About 25% of hermatypic corals (stony corals)
form single sex (gonochoristic) colonies,
while the rest are hermaphroditic.
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About 75% of all hermatypic corals "broadcast
spawn" by releasing gametes—eggs and
sperm—into the water to spread offspring.
The gametes fuse during fertilization to form
a microscopic larva called a planula.
all corals spawn on the same night
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Budding involves splitting a smaller polyp
from an adult.
Budding can be:
Intratentacular—from its oral discs,
producing same-sized polyps within the ring
of tentacles
Extratentacular—from its base, producing a
smaller polyp
 Atoll
Reef- extends all around a lagoon
without a central island
* when an island sinks below the ocean’s
surface
 Fringing
Reef- directly attached to shore
* grow up to the edge of the shore
 Barrier
Reef- separated from mainland by
lagoon
* only grow when there is a change of sea
level on the coast adjacent from it
* grow where land is sinking faster in the
water