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CyberEd® Student Study Guide
Cnidarians
CyberEd® Student Study Guide: Cnidarians
The following National Science Education Standards relate to this study guide:
BIOLOGICAL EVOLUTION
o Biological classifications are based on how organisms are related. Organisms
are classified into a hierarchy of groups and subgroups based on similarities
which reflect their evolutionary relationships. Species is the most fundamental
unit of classification.
o The millions of different species of plants, animals, and microorganisms that live
on earth today are related by descent from common ancestors.
THE INTERDEPENDENCE OF ORGANISMS
o Energy flows through ecosystems in one direction, from photosynthetic
organisms to herbivores to carnivores and decomposers.
o Organisms both cooperate and compete in ecosystems. The interrelationships
and interdependencies of these organisms may generate ecosystems that are
stable for hundreds or thousands of years.
Page 1
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Table of Contents
Introduction ..................................................................................................................... 3
Cnidarian Evolution ......................................................................................................... 5
Common Cnidarian Features .......................................................................................... 6
Cnidarian Senses, Movement and Digestion ................................................................ 11
Class Anthozoa: Corals ................................................................................................. 13
Class Anthozoa: Sea Anemones ................................................................................... 18
Class Hydrozoa: Hydroids ............................................................................................. 22
Class Hydrozoa: Hydras and Portuguese Man-of-Wars ................................................ 25
The Jellyfish .................................................................................................................. 29
Review .......................................................................................................................... 34
Resources Referenced in this Study Guide
Software Programs
CyberEd Biology Course Title: Cnidarians
Quizzes & Tests
All quizzes and tests referenced in this Study Guide can be located in the Teaching
Resources section of the CyberEd Oasis website.
Lab Activities
All lab activities referenced in this Study Guide can be located in the Teaching
Resources section of the CyberEd Oasis website.
Web Links
All web links referenced in this Study Guide can be located in the Teaching Resources
section of the CyberEd Oasis website.
Page 2
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Introduction
Cnidarians
Now load the CyberEd Biology Course Title: Cnidarians
View scenes # 1 - 4 and then answer the following questions.
Learn where cnidarians fit in the classification scheme of life.
Multimedia
Presentation
Scenes 1 – 2
1.
A Diverse Phylum: These pictures show various cnidarians. Discuss this diversity
in the table below.
Some animals
included in
phylum
Cnidaria
What this
program
examines
Number of
Cnidarian
species, so far
Habitat
jellyfish, sea anemones, corals, and hydras, among others
cnidarian physical similarities and differences, habitats and
behaviors, and relationships with the organisms around them
Scientists have identified over 9000 living species in the
Cnidaria phylum, to date.
All cnidarians are totally aquatic. Most species live in the salty
oceans. Some species, such as the hydras, are found in fresh
water streams and lakes. Although a few species float along the
surface and others are found in deep, cold waters, the majority
of cnidarians live in the shallow depths of warm, tropical
oceans.
Page 3
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scenes 3 – 4
2.
Animal Essentials: These pictures show where
cnidarians fit in the animal kingdom. In the
table below, explain the defining characteristics
of animals and the distinction between
vertebrates and invertebrates.
Three defining
characteristics
Vertebrates
Invertebrates
Relative abundance of
the two
Evolutionary
relationship of the two
1. All animals are made of eukaryotic cells, which are
cells that possess a nuclear envelope.
2. Animal cells DO NOT have a cell wall, which is a
rigid structure found encompassing only the cells of
plants and bacteria.
3. All animals are heterotrophs, meaning they must
obtain nutrient energy by consuming other
organisms.
Vertebrates are animals which possess a vertebral
column, or spine, such as humans and sharks.
Invertebrates such as cnidarians lack a vertebral
column.
Scientific estimates suggest that 95 to 98 percent of all
animal species are invertebrates.
Fossils provide evidence that the vertebrates most likely
evolved from invertebrate ancestors.
Page 4
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Cnidarian Evolution
Cnidarians
Now load the CyberEd Biology Course Title: Cnidarians
View scenes # 5 - 9 and then answer the following questions.
Learn how cnidarians fit into the time scheme of life.
Multimedia
Presentation
Scene 5
1.
Time Frame: This underwater view
portrays early animal life in the
oceans. Discuss cnidarians in the
context of evolutionary time.
Fossils indicate the earliest animals
were invertebrates that lived in the
oceans about 600 million years ago, a
relatively recent era considering the
Earth’s 4.5 billion year history. Some
of the early animals such as
Hallucigenia or Wiwaxia appear
strange and exotic when compared to
modern species. Others resemble the modern day cnidarians. The cnidarians of
today exhibit many of the same structural and functional traits possessed by their
ancestors millions of years ago.
Scene 6
2.
In the table below, discuss the biological meaning of the terms, primitive and
advanced.
What
these
terms
mean
What
these
terms do
not mean
These terms are relative comparisons. Primitive characteristics are
thought to have originated further back in time. Advanced
characteristics evolved later in the species’ history. Members of the
phylum Cnidaria resemble the earliest animals known to exist;
therefore, their characteristics are said to be relatively primitive.
Animals with primitive characteristics should not be considered
disadvantaged or less successful than animals with more advanced
characteristics. The cnidarians’ primitive characteristics have proven
successful for hundreds of millions of years.
Page 5
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Common Cnidarian Features
Cnidarians
Now load the CyberEd Biology Course Title: Cnidarians
View scenes # 7 - 18 and then answer the following questions.
Multimedia
Presentation
Learn about radial symmetry, cnidarian tissues, sac-like bodies, tentacles and
cnidocyte cells.
Scenes 7 – 9
1.
Anemone Pie: This picture shows an
anemone sliced along planes of symmetry. In
the table below, explain cnidarian body
symmetry and level of organization,
comparing it to human symmetry and level of
organization.
What body
symmetry means
Human body
symmetry
Body symmetry refers to the spatial arrangement of body
parts. If an organism’s body can be divided at least once into
equal but opposite parts, then it possesses symmetry
determined by the arrangement of planes of symmetry.
Humans have only one plane of symmetry and are bilaterally
symmetrical with equal right and left halves on each side of
the plane.
Cnidarian
symmetry
Cnidarians can be sliced in half by any plane that passes
through the center axis of the organism. This type of
symmetry is called radial symmetry.
Human body
level of
organization
In humans, cells are organized into tissues, tissues are
organized into organs, and organs are organized into organ
systems.
Cnidarian body
level of
organization
Most cnidarians function at the tissue level of organization. A
tissue is a group of similar cells working together to perform a
specific function. A few cnidarian species possess primitive
organs.
Page 6
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scenes 10 – 11
2.
It’s in the Bag: This illustration shows cut away views of cnidarian bodies. Explain
cnidarian tissues and structures in the table below.
Types and
functions of
tissue
Cnidarians possess only two tissue types. One is the outermost
epidermal layer, or epidermis, which protects the animal from the
outside environment. The other tissue is the innermost
gastrodermal layer, or gastrodermis, which absorbs food nutrients.
Mesoglea
The mesoglea is a gelatinous matrix sandwiched between the
epidermal and gastrodermal tissue layers. It is made mostly of
water and may contain some unorganized cells and fibers. It is not
considered a true tissue layer, but rather, a packing material that
allows many chemicals to diffuse through it.
Cnidarian bodies have only one opening, called the mouth. The
mouth functions as an entrance for food as well as an exit for
waste. The mouth leads to internal pocket called a gastrovascular
cavity.
Mouth
Body shape
The cnidarian body resembles a sac or bag. Biologists call this
single opening type of body a sac-like body.
Page 7
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 12
3.
Inverted Forms: These pictures show a jellyfish and a sea anemone. Explain how
they demonstrate the two basic types of cnidarian body form.
The sac-like bodies of the cnidarians
are found in one of two forms. The
jellyfish shows the umbrella-like
medusa form, the sea anemone
exhibits the column-like polyp form.
The medusa form is an upside down,
compressed version of the polyp form.
Cnidarians in the medusa form
generally
move
about
their
environment by swimming in a
pulsating manner. The polyp form cnidarians have various methods of mobility, or
are sessile, remaining in one place. Most cnidarians show one form or the other;
some cnidarian species can exist in each form during their life cycle.
Scenes 13 – 14
4.
Tentacle Touch: These pictures feature cnidarian tentacles. Explain the variety,
structure and function of cnidarian tentacles.
All cnidarians possess tentacles around the mouth. Tentacles may be short and
stubby like those of the corals and sea anemones, or long and slender like those
of most jellyfish. Some jellyfish species have tentacles that reach 50 meters or
more. Tentacles are extensions of the cnidarian’s body, usually containing
epidermal tissue, gastrodermal tissue, and mesoglea. Although often dangling in
the water currents, these tentacles also have the capacity to extend and contract,
allowing for hunting, movement and self defense.
Page 8
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scenes 15 – 17
5.
Pop Goes the Sting: This
illustration shows the mechanism
and distribution of
cnidocyte cells. In the
table below, explain
how they work.
Where found
Cnidocyte
structure
Cnidocyte
effect
Trigger and
lid action
Stinging,
sticking and
tangling
devices
Fate of fired
cell
Types of
stimuli
embedded within the epidermis of all cnidarians and usually
very concentrated along the tentacles
Cnidocyte cells contain a capsule-like organelle called a
nematocyst, which houses a hollow filament. Depending on
their function, filaments may be covered in a sticky adhesive or
they may be equipped with barbs capable of injecting poisons.
When triggered the tiny filaments spring outward explosively,
either sticking to a surface or delivering a fatal sting. If human
skin accidentally comes in contact with certain jellyfish, the
cnidocyte cells deliver painful and sometimes fatal stings.
The trigger is a modified flagellum called a cnidocil. The lid is
called the operculum. When the cnidocil is triggered by the
proper stimulus, the capsule membrane instantly allows water
to flood into the nematocyst’s inner chamber. The operculum
then flips open and the filament is rapidly ejected outward.
If the nematocyst organelle is designed to sting prey, tiny barbs
will extend outward during discharge. These spikes can pierce
and inject poison into prey. Other types of nematocysts may
secrete a sticky substance which allows the tentacles to attach
to certain surfaces. A third type of nematocyst may recoil like a
spring, entangling the prey so that the tentacles may draw the
food into the mouth.
Once a nematocyst has been discharged, the cnidocyte is
destroyed by the cnidarian’s body.
specific tactile and chemical stimuli, usually in a specific order
that distinguishes the prey so the nematocytes only fire when
appropriate
Page 9
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 18
6.
Borrowed Defense: This nudibranch is
making a meal of a cnidarian polyp. Explain
how animals such as certain mollusks and
flatworms can have cnidocytes.
The cnidarians are the only animals that
develop cnidocytes. The word Cnidaria was
derived from the word cnidocyte. Some
animals, such as the nudibranch shown in
the picture, can eat cnidarians without
triggering the nematocysts to fire. The
nudibranch
then
incorporates
the
cnidarian’s cnidocytes into its own body. Thus, cnidocytes can be found in other
types of animals although only cnidarians can develop these discharging cells.
Page 10
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Cnidarian Senses, Movement and Digestion
Cnidarians
Now load the CyberEd Biology Course Title: Cnidarians
View scenes # 19 - 23 and then answer the following questions.
Multimedia
Presentation
Learn how cnidarian sensory cells stimulate movements, including digestive
reactions.
Scene 19
1.
Web of Nerves: This illustration
portrays the cnidarian nerve net.
Describe how it works.
The nerve net coordinates the
movement of the tentacles and the
body. This intricate structure is
composed of primitive nerve cells
called protoneurons distributed in a
web-like network underlying both
the epidermal and gastrodermal
tissues. Usually, when a part of the
net is excited the impulse spreads
in all directions rather than along a
specific path. Even if only a single
protoneuron is excited, the entire
net quickly becomes stimulated.
Although some cnidarians show
more organization of nerve cells
than others, none have a region centralized enough to be called a brain. The
cnidarians do not even have a distinct body region that can be considered a head.
Scene 20
2.
Hair Trigger: This graphic shows a crab leg and its aura of chemicals touching a
cnidarian sensory cell. Explain this process.
Sensory cells embedded in the epidermis
and mostly concentrated near the mouth
and tentacle regions receive external
messages. These sensors usually contain
a small flagellum capable of receiving
tactile and chemical stimuli, much like the
cnidocil of the cnidocyte cells. The proper
stimuli trigger corresponding nerve
impulses across the nerve net throughout
the body.
Page 11
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 21
3.
Contraction Action: This graphic depicts the contracting parts of cnidarians.
Explain their structure and function.
Although cnidarians do not have any true muscle tissue, tentacle movement and
body contraction are both produced by two types of cells with contracting parts:
the epitheliomuscular cells of the epidermis and the nutritive-muscular cells of the
gastrodermis. Most of the cells in the epidermis are epitheliomuscular cells; an
elongated, contracting portion of each epitheliomuscular cell is situated in the
mesoglea. Similarly, while most of the nutritive-muscular cell is found in the
gastrodermal layer, the contracting portion is found in or adjacent to the mesoglea.
Protoneurons of the nerve net are connected to these muscle-like cells, stimulating
muscle-like contractions.
Scene 22
4.
Digestive Reach: This graphic shows digestion taking place in the gastrodermis.
Explain the processes of extracellular and intracellular digestion in cnidarians.
When prey is pushed into the mouth area,
gland cells embedded in the gastrodermis
secrete digestive enzymes that break down
the prey into smaller food particles. This is
called extracellular digestion because it
occurs outside of the cells. Once food is
broken into smaller bits the nutritivemuscular cells reach out with pseudopodia
and engulf the food particles for intracellular
digestion. Nutrients diffuse throughout the
mesoglea for use by the other cells of the
cnidarian.
Page 12
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Cnidarians
Please load the CyberEd Biology Course Title: Cnidarians
Complete Interactive Lessons # 1 & 2
A review of cnidarian characteristics.
Interactive
Lesson
Cnidarians
Please load the CyberEd Biology Course Title: Cnidarians
Complete Interactive Lesson # 5
A review of hydrozoan digestion.
Interactive
Lesson
Quiz: Introduction to Cnidarians
Please take the quiz provided by your teacher.
Quiz
Quiz: Characteristics of Cnidarians
Please take the quiz provided by your teacher.
Quiz
Page 13
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Class Anthozoa: Corals
Cnidarians
Now load the CyberEd Biology Course Title: Cnidarians
View scenes # 23 - 32 and then answer the following questions.
Learn about coral animals and coral colonies.
Multimedia
Presentation
Scene 23
1.
In the table below list the similar physical characteristics and the four major
classes of cnidarians.
Similar physical
characteristics
The four major
classes
sac-like body, radial symmetry, epidermal and
gastrodermal tissue, mesoglea, tentacles, and
cnidocytes
Anthozoa, Hydrozoa, Scyphozoa, and Cubazoa
Scene 24
2.
Flower Animals: These pictures show two members of the class Anthozoa (one
with a close-up). Identify them and discuss the general characteristics of colonies.
Corals and sea anemones, among others, are “flower animals” in the class
Anthozoa. While the corals are attached to their homes for life, the sea anemones
can tumble, twist, or roll about their environment. The anthozoans can be found
from tropical seas to polar oceans, and they may exist individually or as part of a
colony. A colony is a group of similar organisms living in such close contact that
they are interdependent, sharing responsibilities for survival. Some coral colonies
form islands and reefs.
Page 14
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 25
3.
Coral Belt: These maps
show the distribution of
coral reefs and islands,
and the location of the
famous Great Barrier
Reef. Discuss the reef
ecosystem.
Coral reefs and islands exist in tropical oceans. The
Great Barrier Reef, a region of coral reef and coral
island colonies, extends over one thousand miles and
is home to thousands of animal and plant species.
Coral reefs and islands are ecosystems, defined as communities of organisms
interacting with each other and their physical environment. Coral reefs are
surpassed only by tropical rain forest ecosystems in terms of species diversity,
and they construct their own physical foundation.
Scenes 26 – 28
4.
Cup
by
Cup:
This
illustration shows how
corals build reefs and
islands. In the table below,
explain the process.
Foundation
material
Hermatypic
corals and
their cups
Generation
after
generation
Calcium carbonate, consisting of calcium, carbon, and oxygen,
the same hard substance found in blackboard chalk,
stalagmites, and mollusk shells. Calcium carbonate does not
readily dissolve in sea water.
As they grow, hermatypic corals secrete calcium carbonate to
the outside of their lower epidermal tissue, forming a hard cup
called the coral exoskeleton, within which the sessile coral
polyp spends its entire life. The cup provides a structural
skeleton and protection. If the polyp senses a threat it can pull
itself into the cup.
After coral animals die other polyps build new exoskeleton cups
upon the old ones. Over thousands of years, huge deposits of
calcium carbonate accumulate and eventually become intricate
underwater reefs or islands harboring a plethora of sea life
beside the corals.
Page 15
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 29
5.
Mutual Gains: This graphic depicts the mutualism between reef coral animals and
the algae living inside them. Describe this relationship and how it influences the
growth of coral reefs.
Hermatypic corals produce large amounts of
calcium carbonate with the help of singlecelled algae that live inside their bodies, a
mutualistic relationship that benefits both
organisms. The algae are provided a
protected place to live, while the corals that
house the algae are able to produce calcium
carbonate many times faster than corals
which lack algae. As the algae rely on
photosynthesis for their survival, the
mutualistic corals must reside close to the
surface so that the algae they contain will
receive sufficient sunlight. This is the reason
why many of the world’s largest reefs are found in relatively shallow water.
Scene 30
6.
Coral Gallery: These pictures show a variety of coral colonies that are different
from the hermatypic corals. Briefly describe them.
Some corals, unlike the hermatypic corals, do not secrete skeleton cups. Thorny
corals exhibit exotic exoskeletons that form tree-like structures festooned with
spikes and thorns. The soft corals, sea fans, and sea pens form skeletons
embedded within the mesoglea, an endoskeleton formed inside the animal. At a
distance each of these colonies may look like one animal. Up close, it is apparent
that these forms are elaborate networks of individual polyp corals.
Page 16
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 31 – 32
7.
Cutaway Coral: This graphic shows the inner workings of hermatypic corals. In the
table below, discuss the components of the gastrovascular cavity.
Pharynx
The pharynx is a narrow passageway occupying the area between
the mouth and the main gastrovascular area.
Septa
Septa are partitions within the pharynx and gastrovascular cavity.
They increase the surface area of the gastrodermis, providing
more nutritive-muscular cells to absorb the nutritional elements of
food brought into the gastrovascular cavity.
Within the septa, the contracting portions of the nutritive-muscular
cells run longitudinally, allowing the coral to pull its body inside its
exoskeleton cup.
Some septa do not extend completely to the pharynx. The edges
of these incomplete septa contain gland cells, which secrete
digestive enzymes. In some species, the incomplete septa may
even wield stinging cnidocyte cells.
The lower end of the incomplete septa is often modified into
thread-like structures called acontia, which contain gland cells and
cnidocyte cells. When necessary, acontia can exit the mouth area
and act as extra tentacles. This might happen if captured prey is
too large to fit into the animal’s mouth. Gland cells located on the
acontia threads can secrete their digestive enzymes to partially
digest the prey outside of the polyp. When large food is sufficiently
broken up, it is pulled into the gastrovascular cavity.
Coral
contraction
Incomplete
septa
Acontia
Page 17
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Class Anthozoa: Sea Anemones
Cnidarians
Now load the CyberEd Biology Course Title: Cnidarians
View scenes # 33 - 40 and then answer the following questions.
Learn about sea anemones.
Multimedia
Presentation
Scene 33 – 34
1.
Slow but Sure: These pictures show various methods of sea anemone mobility. In
the table below discuss how sea anemones differ from corals, and how they move
about their habitat.
Comparison with
corals animals
and coral colonies
Mobility via the
pedal disc
Class Anthozoan includes sea anemones, carnivorous
animals with body plans similar to the coral polyps. They are
larger than corals and do not secrete an exoskeleton cup.
Unlike coral colonies, the majority of sea anemones live
independent of other sea anemones, although they may be
crowded close together. While corals are sessile, sea
anemones are somewhat mobile.
Sea anemones have a slightly enlarged lower part of the
body called a pedal disc. They can slowly slide along a
mucus carpet secreted by epidermal cells on the pedal disc.
Mobility via
swimming
Some sea anemones swim by using spastic bending
movements.
Mobility via
tumbling
Some sea anemones can tumble with the currents along the
ocean floor.
Mobility via hitchhiking
Some crabs can pry sea anemones from rocks and place
them atop their backs. The sea anemone hitches a ride; the
crab receives camouflage.
Page 18
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 35 – 36
2.
Squeezing the Incompressible: This graphic
depicts the internal structure of a sea anemone,
and what happens when it squeezes itself
around its circumference. Explain both features.
Sea anemones resemble corals in their internal
structure, with a pharynx leading to the
gastrovascular cavity, incomplete septa ending
in acontia, and complete septa partitioning the
animal. Additionally, sea anemones have well
developed
nutritive-muscular
cells
with
contracting parts that run in a circular belt around
the circumference of the animal. Circular
contractions of these cells push against the noncompressible, water-filled hydrostatic skeleton,
squeezing the body longer.
Scene 37
3.
Single Parent Family: This graphic shows two ways a sea anemone can produce
identical genetic copies of itself. Discuss asexual reproduction in sea anemones
and corals.
In sea anemones, asexual reproduction
frequently occurs by longitudinal fission, the
animal dividing in half by creating a new body
wall down the middle of itself. Asexual
reproduction also occurs when a piece of the
pedal disc is detached as the animal glides
along. If the piece is left on a suitable habitat, it
will grow into a new sea anemone. This is
termed
regeneration
from
fragmentation.
Similarly, corals also have the ability to asexually
reproduce if a piece of their body happens to
break off and land in a hospitable spot.
Page 19
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 38 – 39
4.
Rendezvous for Two: This graphic
illustrates contrasting modes of
sexual reproduction in anthozoans.
In the table below, explain sexual
reproduction in general, and how it
works with sea anemones and
corals.
Sexual
reproduction
Anthozoan
sexes
Internal
fertilization
External
fertilization
A new organism forms through the combination of male and
female sex cells, or gametes. Male gametes are called sperm
and female gametes are called eggs. When a sperm cell and an
egg cell combine it is called fertilization.
Some anthozoans can produce only sperm, or only eggs; other
anthozoan species are hermaphrodites, producing sperm and
egg alternately to avoid self fertilization.
In species that utilize internal fertilization, the eggs reside on the
septa inside the gastrovascular cavity, and are fertilized by
sperm from another anthozoan.
During external fertilization, the most common mode in
anthozoans, sperm and egg from two animals are released to the
open water where they combine. Some anthozoans exhibit mass
fertilization, with thousands of individuals in the span of one night
releasing their sperm and eggs simultaneously to the sea.
Scene 40
5.
Round and Round: This graphic
depicts the life cycle of sea
anemones. In the table below,
explain the steps in that cycle.
Fertilization
Zygote
Larva
Adult body
form
Sex cells from two adults combine to produce a zygote.
The zygote grows into a ciliated larva.
Upon settling, the larva grows directly into a new adult.
The only type of body plan exhibited by the adult sea anemone is
the polyp type. There are no known anthozoans with the medusa
body plan.
Page 20
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Quiz: Anthozoans
Please take the quiz provided by your teacher.
Quiz
Cnidarians
Please load the CyberEd Biology Course Title: Cnidarians
Complete Interactive Lesson # 6
A review of anthozoan structures.
Interactive
Lesson
Page 21
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Class Hydrozoa: Hydroids
Cnidarians
Now load the CyberEd Biology Course Title: Cnidarians
View scenes # 41 - 45 and then answer the following questions.
Learn about hydrozoan varieties, and hydroids in particular.
Multimedia
Presentation
Scene 41
1.
This picture shows three species of hydrozoans. In the table below, discuss class
Hydrozoa.
Hydrozoan
habitats
Life cycle body
plans
Comparison with
anthozoans
Solitary and
colonial lifestyles
Three different
hydrozoans
mostly marine, some freshwater
Some Hydrozoan species show only the polyp form, some
exhibit both polyp and medusa forms in their life cycle.
Hydrozoan polyps generally are much smaller than
anthozoan polyps, and in some species are significantly
modified.
Some hydrozoans are solitary; most are colonial,
permanently attached to the ocean floor or hard surface.
Some colonies float on the surface.
colonial hydroids; the solitary hydras; and colonial
Portuguese man-of-wars
Page 22
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scenes 42 – 44
2.
Many from One: This illustration shows the development of an entire hydroid
colony from one larva. In the table below, describe the process and the result.
From larva to
colony
A ciliated larva settles on a suitable surface and grows
into a polyp. The polyp puts out root-like structures called
hydrorhiza which serve as an anchor. The anchored polyp
undergoes asexual reproduction through budding—the
growth of a new organism from the surface of the parent.
This asexual budding produces an entire hydroid colony.
Zooids, the
gastrovascular
cavity, and the
perisarc
Each new bud grows into an individual animal called a
zooid. Zooids are connected by a common gastrovascular
cavity through the base and stalk, walled with inner
gastrodermal tissue, the mesoglea, and outer epidermal
tissue. Cells with whip-like flagella line the gastrodermis,
circulating water and nutrients throughout the colony. The
base and stalk are covered by a sheath of protective
material called the perisarc. In some hydroid species the
perisarc also covers the individual zooids.
Individual zooids in a colony have different functions and
appearances. Gastrozooids are the food suppliers of the
colony, stinging their prey with nematocyst studded
tentacles and pushing the food into their mouths for
digestion. Zooids called gonangiums are reproductive
structures, producing medusoid buds that eventually break
away from the colony.
Zooid specialization
Page 23
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 45
3.
Both Body Types: This graphic depicts the full life cycle of hydroids. Starting with
the medusoids, describe the progression.
The medusoid buds of hydroids
have the medusa body plan.
They swim using rhythmic
undulation. Medusoids develop
into adult organisms a few
millimeters in diameter called
the
hydromedusae,
which
conduct sexual reproduction.
The female hydromedusae
shed eggs to the open water
and the males release sperm.
This
external
fertilization
results in ciliated larvae, which
settle down to renew the
hydroid life cycle by becoming
hydroid polyps. Thus, the
hydroid life cycle includes stages of both polyp and medusa body types.
Page 24
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Class Hydrozoa: Hydras and Portuguese Man-of-Wars
Cnidarians
Now load the CyberEd Biology Course Title: Cnidarians
View scenes # 46 - 51 and then answer the following questions.
Learn about hydras and Portuguese man-of-wars.
Multimedia
Presentation
Scene 46 – 47
1.
Freshwater Creatures: This illustration shows the structure of another hydrozoan,
the hydra, and some of the ways it moves about its habitat. In the table below,
describe hydra bodies, habitats, and mobility.
Body type,
lifestyle and
size
Habitat
Cnidarian
features
Mobility
modes
Hydras exist only as independent polyps a few centimeters in
length.
Unlike other cnidarians, they inhabit freshwater lakes and
streams throughout the world, attaching to aquatic plants.
Hydras are often used in research because they are
widespread.
Hydras have the cnidarian epidermis, mesoglea, and
gastrodermis. Their tentacles are studded with stinging
cnidocyte cells.
They can slowly glide along their basal disc, or pull themselves
forward with their tentacles, or perform acrobatic flip-flops, or
float by producing a small gas bubble on the basal disc.
Page 25
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 48
2.
Head Start: this graphic shows the
hydra’s
namesake,
the
mythological monster Hydra, which
could grow back a decapitated
head. Discuss the methods for
hydra asexual reproduction shown
in the illustration.
Halves of a cut hydra will grow into
two hydras. Severed tentacles will
soon grow back. This type of
asexual reproduction is termed
regeneration, and mainly functions
to replace lost tentacles. Rarely is
a new animal reproduced this way. More commonly, asexual reproduction in hydra
takes place through budding. The new hydra first appears as a small bud off the
side of the parent, eventually growing almost as large as the parent before
detaching to float away and live on its own. In addition to budding, hydras also
have the ability to regenerate from fragments, like the corals and sea anemones.
Scene 49
3.
Winter Break: This graphic depicts the climate-sensitive life cycle of hydra. Starting
with sperm and egg, describe the process.
Sexual reproduction of the hydra occurs
internally. An ovary containing eggs is
produced as an outgrowth on the female’s
body. Sperm released to the water from
the male hydra swim into the female
hydra’s mouth and fertilize the egg. The
fertilized egg develops while attached to
the female hydra; a protective covering
forms
around
it.
Eventually,
the
developing embryo, enclosed in the
protective covering, detaches from the
parent. This cyst allows the new hydra
embryo to survive harsh winter conditions.
When conditions are favorable, the
embryo is released and continues
developing directly into an adult hydra.
The hydra life cycle does not include any
medusa type body plan.
Page 26
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 50 – 51
4.
Floating Colony: These pictures
show a Portuguese man-of-war, the
full length of the tentacles are not
shown. In the table below, describe
its organization, life style, and
specialized parts.
.
Overall
organization
The Portuguese man-of-war is a colony of polyps, not a
single organism.
Pneumatophore
form and function
One of the highly modified polyps is a float, called a
pneumatophore. The pneumatophore contains air rich in
carbon dioxide.
Hunting strategy
Portuguese man-of-war colonies drift along the ocean
surface, using the polyps dangling in the water to harvest
small fish.
The hanging tentacles are individual polyps, or zooids.
Each zooid has a single, long tentacle that extends 10
meters or more. These tentacles deliver fatal stings to
small fish, and can inflict serious injury upon humans.
Zooid specialization Some of the zooids are designed for feeding and have a
single mouth. Others lack a mouth and specialize in
entangling prey. Still, other zooids are specially designed
for reproduction.
The man-of-wars, and some other colonies like them, are
Comparison with
the most modified of the hydrozoan cnidarians
other hydrozoans
Hanging tentacles
Page 27
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Quiz: Hydrozoans
Please take the quiz provided by your teacher.
Quiz
Page 28
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
The Jellyfish
Cnidarians
Now load the CyberEd Biology Course Title: Cnidarians
View scenes # 52 - 60 and then answer the following questions.
Learn about scyphozoans and cubazoans.
Multimedia
Presentation
Scenes 52 – 53
1.
Medusa Shapes: These pictures show two types of jellyfish. Discuss them.
Jellyfish are not really fish but they do have a
large layer of jelly-like mesoglea. The
scyphozoans have bell-shaped medusa
bodies; the cubazoans have cube-shaped
medusa bodies. Both scyphozoans and
cubazoans can be found floating or
swimming in most oceans at most depths.
Scyphozoans and cubazoans contain many
of the same structures and functions. Most
jellyfish are between 5 and 50 centimeters in
diameter, and one species measures six feet
across with tentacles as long as a ten story
tall building. Jellyfish may be colorless or
colorful; most are semi-transparent.
Scene 54
2.
Delicate Anatomy: This graphic depicts the body parts of a jellyfish. Describe the
jellyfish anatomy, referring to the labels in the picture.
Most jellyfish are delicate, graceful,
animals, best known for their beautiful
medusa forms. The top part
of the jellyfish is the
exumbrella; the lower is the
subumbrella. Hanging from
the subumbrella of most
scyphozoan jellyfish is a structure called
the manubrium. The opening of the
manubrium is the mouth of the animal.
Oral arms with oral lobes extend from the
manubrium, appearing like tentacles.
However, a jellyfish’s actual tentacles are
located along the margin that separates
the exumbrella from the subumbrella.
The number of tentacles varies among different jellyfish.
Page 29
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scenes 55 – 56
3.
Sensor Device: This illustration shows a rhopalium and its two components, the
ocellus and the statocyst. In the table below, explain these sense organs.
Rhopalia
(singular:
rhopalium)
Rhopalia exist at regular intervals along the margin between the
exumbrella and the subumbrella. They are among the most
primitive animal sense organs, consisting of two different
structures.
Statocysts
Statocysts in the rhopalia give the animal its sense of balance,
allowing it to discern up from down. Statocysts are small round
chambers lined internally with sensory hairs, enclosing tiny, hard
particles called statoliths. As the animal tilts, the statoliths roll by
gravitational pull inside the chamber, touching hairs which, in
turn, send signals to the animal’s nerve net. Thus, the jellyfish
can right itself.
Ocelli in the rhopalia sense photon energy, allowing the animal
to detect brightness. They are not considered true eyes,
although in some cubazoans, ocelli are so well developed that
biologists consider them primitive eyes. In most jellyfish, the
ocelli are primitive structures which measure the relative light
intensity in the water, assisting the jellyfish in determining
danger, prey, or perhaps shelter.
Ocellus
(plural: ocelli)
Page 30
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scenes 57 – 58
4.
Fish Snack: This graphic
shows a jellyfish eating a true
fish. Describe the entire
process, referring to the
numbered steps.
Tentacles
A small fish bushes the tentacles of the jellyfish and is paralyzed by
the powerful stings of the cnidocyte cells. This is shown at step 1.
Oral arms
Using cilia located along the oral arms, the jellyfish slowly moves the
fish toward its mouth. This is shown at step 2.
Gastric
pouches
As the prey is forced into the mouth, it encounters gastric pouches
that lie just internally to the manubrium. The cells lining these
pouches secrete digestive enzymes into the pouch space for
extracellular digestion. This is shown at step 3.
Radial
canals
Once the food is extracellularly digested, the nutrients are passed to
the radial canals by water currents. The radial canals are hollow,
tube-like extensions from the gastric pouches, leading radially
toward the edge of the invertebrate. As the nutrients travel through
the canals, they are absorbed by gastrovascular cells.
The radial canals ultimately terminate at the ring canal, encircling the
animal along its outermost margin. The ring canal also contains
gastrovascular cells for nutrient absorption.
Ring canal
Page 31
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Scene 59 – 60
5.
This diagram portrays the life cycle of a scyphozoan. In the table below, explain
the phases in this life cycle.
The two body
type stages,
overall
larva to
scyphistoma
The typical jellyfish life cycle includes a short polyp stage and
a predominant medusa stage.
Strobila and
ephyra
Medusoid-like buds are produced asexually in a process
termed strobilation. Each bud is called an ephyra, and the
overall structure is known as a strobila.
The ephyrae of the jellyfish strobila eventually detach and
develop into free-swimming medusa jellyfish adults.
Ephyra to adult
Sexual
reproduction
Fertilization to
larva
When a ciliated larva settles on the ocean floor, it grows into a
tentacled polyp known as a scyphistoma.
Male and female jellyfish produce sperm and eggs within
structures called gonads located in the gastric pouches.
Sperm are released into the water in order to fertilize eggs
residing within the female’s gastric pouch or on the fold of an
oral lobe.
Successful fertilization produces a zygote that either develops
within the fold of an oral lobe or is released to develop in the
open water. Eventually, this zygote becomes a free-swimming
ciliated larva and the life cycle continues when the larva
settles to the ocean floor.
Page 32
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Cnidarians
Please load the CyberEd Biology Course Title: Cnidarians
Complete Interactive Lessons # 8 & 9.
A review of the scyphozoan features and lifecycle.
Interactive
Lesson
Quiz: Scyphozoans & Cubazoans
Please take the quiz provided by your teacher.
Quiz
Page 33
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Review
Cnidarians
Now load the CyberEd Biology Course Title: Cnidarians
View scene # 61 and then answer the following questions.
Review what you have learned about cnidarians.
Multimedia
Presentation
Scene 61
1.
In the table below, review what you have learned.
Common Cnidarian
external
characteristics
radial symmetry, tentacles, stinging cnidocyte
Range of body
types
Some species have polyp bodies, some have medusa
bodies, and some might even have both at different stages
of their life cycle.
Range of mobility
While some are sessile animals, such as the colonial
corals and colonial hydroids, others possess the ability to
move about their aquatic environments, such as the
hydras, jellyfish, and most sea anemones.
Range of
reproductive
strategies
Reproduction methods may be sexual, asexual, or both,
depending on the species.
Primitive
characteristics
The headless, sac-like body, with only one opening, is
considered a primitive body plan within the animal
kingdom. Other primitive invertebrate characteristics
include their nerve net, gastrovascular cavity, and true
tissue level of organization.
Jellyfish possess primitive sense organs, but this is not
typical of most cnidarians.
Sense organs
Page 34
© 2003 CyberEd, Inc.
CyberEd® Student Study Guide: Cnidarians
Cnidarians
Please load the CyberEd Biology Course Title: Cnidarians
Complete Interactive Lessons # 3 & 4
A review of cnidarians.
Interactive
Lesson
Cnidarians
Please load the CyberEd Biology Course Title: Cnidarians
Complete Interactive Lesson # 7
A review of sexual and asexual reproduction.
Interactive
Lesson
Comprehensive Exam: Cnidarians
Please take the exam provided by your teacher.
Test
Page 35
© 2003 CyberEd, Inc.