Invertebrates
When Carl Linnaeus first created his method for
organizing animals, he had just two families of
invertebrates:
Insecta (insects) and Vermes (worms).
Since that time, scientists have found more
invertebrates and have created more
classifications. We will talk
about six main categories or
families of invertebrates.
T h e f i r s t f a m i l y we wi l l l o o k a t i s c a l l e d “ P o r i f e r a . ”
(p r o n o u n c e d : p o r - i f - u r - u )
The “kitchen sponge”
Basic facts about Porifera:
The main member of the Porifera family is the sponge.
That doesn’t mean it is a small family. There are several
thousand different kinds of sponges.
Sponges are a very simple animal. They have no brain,
internal organs, blood, eyes, or ears. They do not have
nervous, digestive or circulatory systems.
Sponges rely on having water constantly flow through their
bodies to obtain food and oxygen and to remove wastes
from their bodies. They attach themselves to the bottom
of the ocean or to the sides of underwater mountains.
Water is continually passing over them, going through
pores and making it possible for them to filter food
particles from the water. Sponges are nature’s natural
water filter!
Click on this “stovepipe
sponge” to watch a
demonstration of sponges
at work filtering water.
Click on the “glass sponge” to
view scientists going down the
Cayman wall to view sponges
in the ocean.
• To review, what animal is in the porifera group?
• How does it get what it needs to survive?
• What kinds of food do you think it gets through those tiny
holes?
• What root word do you hear in the word “porifera?”
• How can that help you remember that a sponge is in the
porifera group?
If you have a sponge, take it out and look at it closely with
your magnifier. What do you notice?
T h e n e x t i n v e r t e b r a t e g r o u p we wi l l l o o k a t i s t h e
C n i d a r i a n s f a m i l y (p r o n o u n c e d : n i e - d a r e - e e - u n s
N o t e : t h e i n i t i a l ‘ c ’ i s s i l e n t ).
T h i s f a m i l y h a s t wo g r o u p s . O n e c o n t a i n s t h e
a n e m o n e s a n d c o r a l s (c l a s s i f i e d a s “ A n t h o z o a ” t h e n a m e c o m e s f r o m t h e G r e e k wo r d s á n t h o s –
“ f l o we r ” a n d z ó a - " a n i m a l s " , h e n c e a n t h o z o a =
" f l o we r a n i m a l s , “ wh i c h f i t s t h e m we l l b e c a u s e o f
t h e i r f l o we r - l i k e a p p e a r a n c e . )
The other members of the Cnidarians family are the
jelly fish.
Basic facts about Cnidarians:
The cnidarians group contains over 10,000 species of
animals.
Their bodies are made of a non-living jelly-like substance.
They have muscles, nervous systems, and some have
sensory organs.
Cnidarians are distinguished from all other animals by
having special cells containing toxins that fire like
harpoons and are used mainly to capture prey. That’s
why you can get quite a sting from jellyfish. The “stingers”
on jellyfish hang down, and the “stingers” on anemones
stick up.
Most cnidarians prey on organisms ranging in size from
microscopic organisms called plankton to animals several
times larger than themselves. Many feed on algae and
parasites.
These animals have to watch out because there are other
animals that like to eat them: starfish, sea slugs, fish, and
turtles like to eat coral, anemones, and jelly fish.
Click on the jellyfish below to see a short clip about jellyfish
from National Geographic:
• To review, what animals are members of the cnidarians
family?
• What are some things that make cnidarians different
from porifera?
• How are these animals helpful to the world?
A third group of invertebrates is the Echinoderms
(p r o n o u n c e d : e e - k i n e - o a - d e r m s ).
T h e wo r d “ e c h i n o d e r m ” m e a n s “ s p i n y s k i n n e d . ”
M a n y e c h i n o d e r m s a r e c o v e r e d wi t h s p i n e s .
Most adults are easy to recognize because of their
f i v e - p o i n t , r a d i a l s y m m e t r y , wh i c h m e a n s m a n y
E c h i n o d e r m s l o o k t h e s a m e o n b o t h s i d e s wh e n c u t
in half.
This class includes
familiar animals like sea
stars, sea urchins, sand
dollars, and sea
cucumbers.
Echinoderms are often recognized
because they have appendages or
patterns in their bodies in multiples of five.
Echinoderms are a little more sophisticated than
Cnidarians as they have a digestive system.
Many have a skeleton on the inside of their bodies, but no
backbone.
One of the most notable
characteristics of echinoderms is their
ability to regenerate tissue, organs,
limbs. For example, if a starfish loses a
leg, it can grow a new one! In some
cases, they can completely
regenerate from a single limb.
These colorful animals have defense mechanisms to help
protect them from predators; some have spines, and
others possess toxins in their bodies that hurt a predator
when they bite them or that can be sent out through their
tube-like feet.
Crabs, sharks, otters, and sea birds
like to eat echinoderms. In addition
to being food for larger animals,
they also provide habitats for
parasites, including crabs, worms,
and snails.
Echinoderms also help build land. Their bone-like
skeletons are major contributors to many limestone
formations throughout the world.
• Let’s review some things we learned about echinoderms.
• What number is common among most echinoderms?
• If a starfish loses a leg, what is the special thing it can do?
What is that called?
• How are echinoderms helpful?
• How can echinoderms defend themselves from predators?
• What is another name for echinoderms?
S n ail s , s l u gs , c l a m s, oys t ers, oc t op us , a n d s q u id
a re al l p art of t h e n e x t grou p of in v e rteb rates
w e w il l l ook at . Wh a t is s im il ar a b out t h e
b odie s of t h ese a n im a ls?
The Mollusca family (pronounced: mul-us-ku), commonly
known as “mollusks,” are a group of invertebrates that
have soft bodies.
There are a variety of members of the mollusca family,
some with hard shells that provide protection, and others
that do not have a hard shell to protect their soft bodies.
Mollusks have more highly-developed
body systems than the other invertebrates
we have looked at so far. In fact, the
squid and octopus have very sophisticated
nervous systems.
Besides being “smart,” the giant squid and the colossal squid
are also the largest animals of all the invertebrate families. A
colossal squid was discovered that was 10 meters (33 ft) long
and weighed 500 kilograms (1,100 lb)!
This picture gives
you an idea of how
large that squid
would look along
side an adult
scuba diver.
Have you been to a beach? You have probably found the
remains of many mollusks:
Mollusks have been an
important food source for
humans for hundreds of years.
Other animals eat them,
as well.
Additional uses of mollusks by
humans include using the
shells to trade as a form of
currency, harvesting pearls
from oysters and mussels, and even the production of a
special dye called “Tyrian purple” used to dye royal robes
back before the time of Christ.
Here are a few questions to consider about the Mollusca
family:
• Where do most mollusks live?
• How can mollusks be helpful to people?
• What is a mollusk you have eaten?
• What is a mollusk you would like to see?
Where do most of the invertebrates we’ve looked at so far
live?
There are two more main classes of invertebrates, and these
groups have some members that live in the water and many
that live on land. The first is worms, and the second is
arthropods.
What follows is a brief introduction to these back-boneless
animals. You will learn about these families in greater detail
in the next few lessons.
Wo r m s a r e t h e f i f t h c l a s s o f i n v e r t e b r a t e s we ’ l l t a l k
about.
Wo r m s h a v e l o n g , t u b e - l i k e b o d i e s a n d n o l e g s .
Wo r m s c a n b e m i c r o s c o p i c (v e r y s m a l l ! ); t h e y c a n
also be as long as a meter stick!
They live in various places —oceans,
f r e s h wa t e r , o n l a n d , o n p l a n t s , a n d
even in animals.
Wh e r e h a v e y o u s e e n wo r m s ?
T h e l a s t c l a s s o f i n v e r t e b r a t e s we wi l l t a l k a b o u t
a r e t h e A r t h r o p o d s (p r o n o u n c e d : a r - t h r o w- p o d s ).
This is the largest group of invertebrates, and you
see members of this family nearly every day.
A r a c h n i d s (s p i d e r s a n d s c o r p i o n s ), i n s e c t s , a n d
crustaceans are all part of this family.
The main characteristics of this family is that they
g e n e r a l l y h a v e e x o s k e l e t o n s (s k e l e t o n s o n t h e
o u t s i d e o f t h e i r b o d i e s ), j o i n t e d l e g s , a n d
segmented bodies.
Have you ever seen a crab? Crabs have a hard
shell on the outside. This exoskeleton protects the
soft insides of their bodies.
Can you think of any insects that have hard
coverings on the outside of their bodies?
Look closely at the legs of this ant. Can you see
h o w t h e y h a v e s e v e r a l p l a c e s wh e r e t h e l e g s
bend? They have six jointed legs.
A n d wh a t d o y o u n o t i c e a b o u t t h e
shape of its body?
How are the bodies of Arthropods the same as your
body?
How are they different?
These six families make up a majority of the
invertebrates in the world, though there are
additional families we could study, also.
Tell your teacher what you can remember about
each group. (You are welcome to go back
through the slides to review as needed.)
•Porifera (pronounced: por-if-ur-u)
•Cnidarians (pronounced: nie-dare-ee-un
Note: the initial ‘c’ is silent)
•Echinoderm (pronounced: ee-kine-oa-derm )
•Mollusca (pronounced: mul-us-ku)
•Worm
•Arthropod (pronounced: ar-throw-pod).
The invertebrate family contains some unique and
exciting animals! Be on the lookout for
i n v e r t e b r a t e s t h i s we e k – y o u s h o u l d f i n d q u i t e a
f e w. R e m e m b e r , t h e y o u t n u m b e r v e r t e b r a t e s ,
including us, 9 to 1!