Transcript Invertebrates - Cobb Learning

Invertebrates
Phylum
Cnidaria
Cnidarians

Phylum Cnidaria

Includes jellyfish, anemones, corals, & sea pens

Next level of complexity after sponges

Tissues are specialized to perform specific
functions.

Also called coelenterates
This term is not used
often anymore!
Coelenterates
Even though not used often anymore…
Refers to 2 Phylums combined:
Phylum Cnidaria & Phylum Ctenophora
-
Ctenophora:
-
Cnidaria:
•
Have a hollow body cavity, & very
simple tissue organization
Comb Jellies
Jellyfish, Sea anemones, Corals, & Sea pens
Cnidarians

Have NO bones

Have NO heart

Have NO brain

Have NO “real” eyes

Have NO respiratory system
Cnidarians: Body Plan

Display radial symmetry, which is a
regular arrangement of similar body
parts around a central axis.


Look the same from all sides
Have no head, front, or back
Cnidarians: Body Plan
Have an oral surface where the mouth is
& an aboral surface on the opposite
side.
Occur as 2 basic forms:
Polyp: A sac-like attached stage (sessile)
Medusa: Bell-like stage
Polyp
Medusa
Some experience both forms during their life time, and
others spend their entire lives as one of the two forms.
Cnidarians: Anatomy

Have a centrally located mouth surrounded by
tentacles which are slender, finger like
extensions.

Use tentacles to catch & handle food
Cnidarians: Anatomy
 The
mouth opens into a gut (enteron)
where food is digested.
- The gut has only one opening, the
mouth.
Cnidarians: Anatomy

The mesoglea is extremely thick, has a
jelly like consistency & makes up the
largest portion of the animal
This is how jellyfish got their name.
Tentacles
 They
capture small prey by discharging
their cnidocytes (stinging cells), which
are unique structures found on the
tentacles.
How Cnidarians Sting

At the narrow outer edge of the cnidocyte is a
short trigger hair called a cnidocil (“trigger”).
Upon contact with prey, the
contents of the nematocyst are
explosively discharged, firing a
dart-like thread containing
neurotoxins.
How Cnidarians Sting

These stinging cells contain poison arrows
connected to threads called nematocyts.
* Cnidarians can still sting when they are dead!!
Tentacles

The tentacle then brings the victim to the
mouth to be digested.

The food passes through the body cells, and
the waste must go back out of the mouth.
Jellyfish Eating
Cnidarians: Anatomy

2 Layers of cells form the body wall
- Ectoderm: external layer
- Endoderm: internal layer that lines the gut
Feeding
Zooplankton: Drifting microscopic animals
Feeding
Phytoplankton: Drifting microscopic plants.
Feeding

After paralyzing its prey, a cnidarian pulls the
prey through its mouth and into its
gastrovacular cavity.
 Gastrovascular
Cavity: A digestive
chamber with one opening.

Food enters & waste leaves the body through
that opening.
Response to Environment


Cnidarians gather information from their
environment using specialized sensory cells.
Both polyps & medusas have a nerve net.
Nerve Net: A loosely organized network of
nerve cells that together allow cnidarians to
detect stimuli such as the touch of a foreign
object.
Response to the Environment

Cnidarians have statocysts which are
groups of sensory cells that help determine the
direction of gravity.

Ocelli are eyespots made of cells that detect
light.
Movement
Hydrostatic Skeleton:
consists of a layer of
circular muscles & a layer of longitudinal muscles that
together with the water in the gastrovascular cavity,
enable the cnidarian to move.
•
Medusas move by jet propulsion.
•
Muscle contractions cause the bell-shaped body to
close like a folding umbrella.
•
This action pushes water out of the bell, moving the
medusa forward.
Cnidaria Reproduction
 Some reproduce asexually by budding (in polyps)

Some reproduce sexually by releasing gametes.

Some sexual forms are monoecious and others
are dioecious
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Eggs and sperm are released into the stomach
and then through the mouth into the sea.
Cnidaria Reproduction

In some cases, to reproduce, a male releases
his sperm into the surrounding water (spawn).

The sperm then swims into the mouth of the
female jellyfish, allowing the fertilization of the
ova.
Cnidarian Reproduction

In other cases, sexual reproduction takes place
with external fertilization in water:
External Fertilization: Takes place outside
the body.
The male & female releases eggs
and sperm at the same time.
Types of Cnidarians
Class Hydrozoa
Types of Cnidarians: Hydrozoans
Class Hydrozoa
Hydra
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They can be found in most unpolluted freshwater ponds, lakes, and streams
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They are usually a few millimeters long and are
best studied with a microscope
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Hydra has a tubular body secured by a simple
adhesive foot called the basal disc.
Types of Cnidarians: Hydrozoans
Class Hydrozoans
Hydra
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At the free end of the body is a mouth opening
surrounded by one to twelve thin, mobile
tentacles.
-
Hydras are generally sedentary
or sessile, but can move,
especially when hunting.
Types of Cnidarians: Hydrozoans
Hydra
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They move by bending over and attaching themselves
to the substrate with the mouth and tentacles & then
release the basal disc.
-
The body then bends over and makes a new place of
attachment with the foot.
-
They “inch-worm” or
“somersault” to move
Types of Cnidarians: Hydrozoans
Class Hydrozoa
Portuguese man-of-war
Consist of feather or bushy colonies of polyps.
- Some polyps are specialized floats, which
may be gas-filled
- Other polyps form the long tentacles used to
capture prey.
Types of Cnidarians: Hydrozoans
Portuguese Man-of-War
Click here for Video!
Types of Cnidaria
Class Scyphozoa
Types of Cnidarians: Scyphozoans
Class Scyphozoa
 Includes jellyfish
 Have a rounded body, or bell.


Swim w/ rhythmic contractions of the bell, but
swimming ability is limited & are carried by
ocean currents.
Class
Scyphozoa
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95% of body is made of water

Here before dinosaurs and sharks
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Inhabit all oceans of the world
Moon Jellyfish also called Common Jellyfish
Moon Jellyfish Life Cycle
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Planula
Each jellyfish is either male or female
1. Males release sperm into surrounding water
2. Eggs get suck in pits on the oral arms, and are
fertilized by sperm
3. The egg develops into a planula
 Planula is the larval stage, small, & covered in cilia
4. The planula settles on a hard surface & develops into
a polyp to become sessile
Moon Jellyfish Life Cycle
5. The polyp begins reproducing asexually by budding,
and now called a scyphistoma
6. Budding produces miniature medusae called
ephyrae
7. After ephyrae are released, they gradually grow into
adult forms
Class Scyphozoans:
Importance
* Jellies are considered a delicacy by many
people.
* Low in fat & calories
* Rich in nutrients.
* Others claim they taste like rubber bands.
Class Scyphozoans:
Importance
* Food source for fish, sea turtles, and other
organisms
Looks like a Jellyfish to sea, but isn’t!
Clear plastics (such as bags and balloons) are often mistaken for
jellyfish by animals such as the endangered leatherback sea
turtle. When they eat plastic, these animals will often starve to
death as the plastic clogs their intestines and they can no longer
digest food.
Save the Sea Turtles!
Recycle Plastic Bags
& Make sure they do not find their way into the ocean!
Class Cubozoa
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Some are among the most dangerous marine
animals.
* Sea wasp, also known as the box jellyfish, of
Australia & Southeast Asia
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Extreme pain immediately when touched by tentacles
Within minutes, heart failure may occur