Transcript cnidaria notes powerpoint

PHYLUM CNIDARIA
CNIDARIAN LIFE HISTORY
Over 9000 species in Phylum
Cnidaria
 Fossil cnidarians date to 700
mya
 All cnidarians have specialized
cells


Cnidocyte
 Contain a specialized stinging
organelle called the Nematocyst
 Found only in this phylum –
nowhere else in the animal
kingdom
CNIDARIAN LIFE HISTORY

Cnidarians are mostly found in shallow, marine
environments but a few are freshwater – none
are terrestrial
CNIDARIAN LIFE HISTORY

Involved in symbiotic relationships
 Algae in reef building coral are critical to reef
formation
 Cnidarian diet is almost exclusively algae
 Algae also feeds other reef inhabitants
CNIDARIAN LIFE HISTORY

4 Classes of Cnidarians

Hydrozoa
CNIDARIAN LIFE HISTORY

4 Classes of Cnidarians

Schypozoa
CNIDARIAN LIFE HISTORY

4 Classes of Cnidarians

Cubazoa
CNIDARIAN LIFE HISTORY

4 Classes of Cnidarians

Anthozoa
CHARACTERISTICS OF CNIDARIA
All are aquatic and most are marine
 Exhibit radial or bi-radial symmetry
 Most have tentacles which are extensible
projections used for food capture

CHARACTERISTICS OF CNIDARIA

Internal body
cavity is called
the gastrovascular cavity
CHARACTERISTICS OF CNIDARIA

Simplest animals
with nerve cells
No nervous
system
 Have a diffuse
nerve net


Covers the
epidermis
CHARACTERISTICS OF CNIDARIA
Simplest animals
with sense organs
the statocyst,which
sense gravity
and the
ocelli, which sense
light intensity

CHARACTERISTICS OF CNIDARIA
Locomotion is by
muscle contractions
with an outer layer of
longitudinal fibers
and an inner layer of
circular fibers
 Body support is a
hydrostatic skeleton


Means it depends on
water pressure
CHARACTERISTICS OF CNIDARIA
Incomplete digestive system with a single opening
serving as both anus and mouth
 No excretory or respiratory system
 Reproduction may be both sexual and asexual

Bud
CNIDARIAN FORM & FUNCTION

2 Basic Body Plans

Polyp is a hydroid form

This is an adaptation to
sedentary life

Tubular body with a mouth
at the oral end surrounded
by tentacles and a pedal
disc for attachment to a
substrate at the aboral end
CNIDARIAN FORM & FUNCTION

2 Basic Body
Plans

Medusa is a
bell or
umbrella
shaped free
swimming
form
CNIDARIAN FORM & FUNCTION

2 Basic Body Plans

Medusa is a bell or umbrella shaped free
swimming form
 The mouth is directed downward and may be
surrounded by tentacles
 Found in true jellyfish, class Schypozoa,
medusa dominate the lifecycle
 In class Hydrozoa both life stages are present
and alternating
CNIDARIAN LIFE CYCLES
Medusa and Polyp
play different roles in
cnidarian life cycles
and the life cycles
differ in the four
classes.
 The zygote develops
into a motile planula
larvae which settles
and develops into a
polyp which may
produce other polyps
asexually by budding

CNIDARIAN LIFE CYCLES
The polyp produces medusa by strobilation
 Medusas are dioecious and reproduce sexually
 True jellyfish in class Schypozoa have a prominent
medusa stage and very small polyps

CNIDARIAN LIFE CYCLES
Most Hydrozoans have both a polyp and a medusa
stage except for the freshwater genus Hydra which
has only a polyp stage
 Class Anthozoa has only a polyp stage

CNIDARIAN CNIDOCYTES
Most Cnidarians are
very effective predators
and this is possible
because of the
cnidocyte. The
Cnidocyte holds an
organelle that is
discharged and contains
either toxins or
paralyzing agents to
render prey helpless
 These organelles are
called cnidae and there
are over 20 different
kinds of them
 The most common is
called a Nematocyst

CNIDARIAN CNIDOCYTES

The cnidocyte contains
the nematocyst,
 a trigger hair called the
cnidocil
 a lid called the
operculum

Both organic
molecules and
vibrations will trigger
nematocyst discharge
 After a cnidae has
discharged, its
cnidocyte is absorbed
and a new one develops

CNIDARIAN CNIDOCYTES

Mechanisms of nematocyst discharge “stinging cells”
 Nematocysts are made of chitin and contain a coiled
filament armed with barbs that may contain poisons
 The cnidocyte cell generates a high osmotic pressure
within the capsule which can reach 140 atmospheres
of hydrostatic pressure
CNIDARIAN CNIDOCYTES



When stimulated with vibrations or prey movement, the
operculum opens and rapidly releases the coiled barbed
threads, this traps the prey and injects the toxin
This is the fastest reaction time in the animal kingodm @
40,000 times the acceleration due to gravity
There are only a few jellyfish that are harmful to humans:

Sea Wasps or the Portuguese Man of War
CLASSES OF CNIDARIA

Class Hydrozoa – (hydra)
 Most hydrozoans are marine and colonial with both
polyp and medusa stages: some freshwater hydra lack
a medusa stage
 Freshwater hydra are found world wide with 16
species in North America.
 The body design is a
small tube with a conical
elevation at one end
called the hypostome
which holds the mouth
surrounded by
6 – 8 tentacles
CLASSES OF CNIDARIA

Class Hydrozoa –
(hydra)
 Feed on a variety of
small crustaceans,
insects and worms
 Entangle prey and
tentacles move trapped
prey to mouth. Inside
the gastrovascular
cavity, gland cells
secrete enzymes to
digest prey.
CLASSES OF CNIDARIA

Class Hydrozoa – (hydra)

Most Hydra are Dioecious and reproduce
sexually by the shedding of eggs and sperm
which are produced by temporary gonads
stimulated by lower temperatures or stagnant
water

Encysted larva survive the winter and young
hydras hatch in spring

Hydras also reproduce asexually by budding
CLASSES OF CNIDARIA

Class Hydrozoa – Colonial Hydrazoans
Hydroid colonies are truly more representative of
Class hydrozoa, genus Obelia is a common example
studies in the lab
 Polyp form is predominate with a base, stalk and
several types of zooids (An animal arising from
another by budding or division, esp. each of the
individuals that make up a colonial organism and
typically have different forms and functions)

Hydranths or gastrozooids are
feeding polyps
 Reproductive polyps are called Gonozoids
which release medusa
 Hydroid medusae are small with a mouth
on the underside of the umbrella bell
 The bell margin holds statocyst and ocelli

CLASSES OF CNIDARIA

Class Scyphozoa – true jellyfish
 Most of the larger jellyfish belong to this class
 Nearly all are free floating in the open sea
 Bells vary in shape and size but all are mostly water 95%
 The margin of the umbrella
bell has indentations, each
bearing a pair of lappets
which hold a club shaped
rophalium which holds a
statocyst that functions
in equilibrium and an
ocelli which
functions in detecting
light intensity.
CLASSES OF CNIDARIA

Class Scypozoa – true jellyfish
The mouth leads to a stomach connected to four gastric
pouches lined with gastric filaments covered with
nematocysts
 Sexes are dioecious and fertilization is internal in the
gastric pouch of the female

CLASSES OF CNIDARIA

Class Scyphozoa – true jellyfish

A complex system of radial canals branch out from the
gastric pouches to connect to a ring canal that circles
the edge of the bell margin, this makes up the nervous
system
CLASSES OF CNIDARIA

Class Cubozoa – the square / box jellies






Square jellyfish with a dominant medusa form and
most species have no polyp form
The umbrella is square with tentacles extending from
each of the four corners
Strong swimmers
Feed mostly on fish
The most deadly of all the
jellyfish are in this class
Irukiandji and Sea Wasp
Irukandji
Sea Wasp
Irukandji sting
CLASSES OF CNIDARIA

Class Anthozoa – the
“flower animals”



Anthozoans lack a
medusa body form
All anthozoans are
polyp & are found in
both deep and shallow
water & vary in size
3 Subclasses of
Anthozoans
Zoantharia – “flower
animals”
 Ceriantipatharia –
“tube anemones”
 Alcyonarian – “soft
corals”

CLASSES OF CNIDARIA

Class Anthozoa – the “flower animals”

Sub-class Zoantharia – “flower animals”
 they are larger and heavier than hydra polyps
 They attach to rocks, timber and some burrow in mud
 A crown of tentacles surround a slit-like mouth
CLASSES OF CNIDARIA


Class Anthozoa – the
“flower animals”
Sub-class Zoantharia –
“flower animals”
 They have a siphonoglyph
which is a ciliated groove
that leads food downward into
the mouth
 When in danger, water is
forcibly expelled through the
mouth and the sea anemone
contracts into a smaller size
 Most sea anemones can glide
slowly on their pedal disc,
some can swim with limited
ability
CLASSES OF CNIDARIA

Class Anthozoa – the “flower animals”
Sub-class Zoantharia – “flower animals”
 Symbiotic relationships include



Hermit crabs
Algae
Clown Fish
CLASSES OF CNIDARIA

Class Anthozoa – the “flower animals”

Sub-class Zoantharia – “flower animals”

Some are dioecious and some are protandrous /
monoecious


Asexual reproduction takes the form of pedal
lacerations when the sea anemone moves to a new
location, a small piece tears off and becomes a new
anemone
Coral Reefs are miniature sea anemones that secrete
CaCO3 cups to live in and then a sheet of living
tissue forms over the calcareous cups that connects all
the gastrovascular cavities, A coral reef is therefore
considered one huge living organism
CLASSES OF CNIDARIA

Class Anthozoa – the “flower animals”

Sub-class Ceriantipatharia – “tube anemones”
 Tube anemones live in soft sediment
 Thorny & black coral form colonies & attach to rocks
 Both are rare and have few species ; live in shallow seas
CLASSES OF CNIDARIA

Class Anthozoa – the
“flower animals”

Sub-class Alcyonarian – “soft
corals”
Show great variation
 Have octomerous
tentacles around mouth
 Include
 Sea Fans, Sea Pens,
Sea Pansies and other
soft corals ; come in
bright colors and help to
create the “submarine
gardens” of the coral
reefs

CORAL REEFS
Have great biodensity rivaled only by the rain
forests
 Living coral is limited to the top layer above the
CaCO3 deposits
 Coral reefs are great recyclers of Phosphorus
and waste

CORAL REEFS



In order to precipitate CaCO3 from seawater,
coral anemones must use CO2 eliminated from
photosynthetic algae, so coral reefs are only
found where algae can grow
They require warmth, light, and full salinity,
and clear water
This limits their growth to 30 N and 30 S of the
equator
o
o
CORAL REEFS

Types of Coral Reefs –

Fringing Reefs – near land with no lagoon or a very
narrow one
CORAL REEFS

Types of
Coral Reefs –

Barrier
Reefs –
parallel to
shore with a
wide and
deep lagoon
Great Barrier Reef
CORAL REEFS

Types of Coral Reefs –

Atoll Reefs – encircles a lagoon with a steep bank on
the seaward side
CORAL REEFS

Types of Coral
Reefs –

Patch or Bank
Reefs – located
some distance
from the shore