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Thank you!

Apologia Biology, Module 11, The Invertebrates of Kingdom Animalia

M11 Recap blog post at Sahm-I-Am
Quizlet Vocabulary Game, M11 

In this module, we're learning about some of the animals without a backbone.  We've got another module about invertebrates, but this module covers some of the more squishy ones.  Some are not quite so squishy as others, and some have protective shells or other protection.
  • Invertebrates - animals that lack a backbone
  • Vertebrates - animals that possess a backbone
• Worms, jellyfish, and snails are invertebrates.
• Insects are invertebrates.  They have no backbone, but have an exoskeleton (a skeleton on their exterior).
• Crawdads (crayfish), lobsters, and shrimp are invertebrates and are classified as crustaceans.  They're kinda crusty.  =)
In the kingdom Animalia, there are way more invertebrates than there are vertebrates.  In fact, all the phyla in kingdom Animalia except one are invertebrates!  That's quite a few!
In this module, we learn about a few of the lesser-known invertebrates and a few you will recognize.

(1) p. 329-331, Symmetry
First let's learn a little about symmetry.  If something is symmetrical, it is usually thought of as being the same on both sides.  There is actually more than one type of symmetry.
  • Spherical symmetry is when an organism can be cut into two identical halves by any cut that runs through its center.  A ball has spherical symmetry.  That's easy, right?
  • Radial symmetry is when an organism can be cut into two identical halves by any longitudinal cut through its center.  This might be from the top, any cut.  Like an oatmeal box can be cut from the top by any cut running straight down through the center.
  • Bilateral symmetry is when an organism can be cut into two identical halves by a single longitudinal cut (only one option, not "any longitudinal cut" as in radial symmetry) along its center which divides it into right and left halves.
If you think about the names of these types of symmetry, you can easily see why they are named this way.
A lot of things have bilateral symmetry.  You can probably look around and see a few things right off.  YOU even have bilateral symmetry.  Probably not exactly, as the two sides of everyone's faces are not an exact replica.  So these symmetry distinctions are not perfect.  Your internal organs are not the same on both sides of your body, either.

Notice the terms on the crayfish above:
  • Dorsal - referring to the back, or it might seem to be the top if the animal is not upright like a human, but it is its back.  Like a dorsal fin on the back of a fish.
  • Ventral - referring to the front, or belly-side of an organism.
  • Anterior - in front of, or the end that contains an organism's head.
  • Posterior - in back of, or the end that contains an organism's tail.
A shark has an anterior dorsal fin and a posterior dorsal fin.  This indicates which is in front of the other; they are both on its back.
Something can also be "anterior to" another body part, meaning it is in front of it, and "posterior to" another body part would mean it is in back of it.


(2)  p. 332-335a, Phylum Porifera:  The Sponges
Did you know that sponges are animals?  Really!
They are not plants.  They can't think; they have no internal organs, no blood, no eyes or ears, but they can reproduce, digest food, and protect themselves.
If you have a sponge from the ocean, it is no longer living.  It would need to stay in the ocean in its environment to be able to eat and stay alive.
How a sponge eats:

Sponges have no symmetry.


(3)  p. 335-341, Phylum Cnidaria
There are 2 Multi-media Companion CD videos to watch for this section.
Members of this phylum have two basic forms, polyp and medusa.
  • In the polyp form, the cnidarian (nih dahr' ee un) is tubelike with a mouth and tentacles at one end, and a basal disk at the other.  A basal disk just means it is circular at the base, often used for attaching itself to something, and there is no opening.  Like a stalk of celery.  
  • In the medusa form, it is free-swimming, with a bell-shaped body and tentacles.  (You may have heard of Medusa from Greek mythology -- ewww!)  It is in this form that we often think of the jellyfish, although a jellyfish has a polyp stage too.
►See diagram of a jellyfish life cycle.

Phylum Cnidaria has radial symmetry.

The members of phylum Cnidaria have some characteristics that are common to all members of this phylum.
Epithelium, mesoglea, and nematocyts, and more.
Read p. 356-357 to understand what they are.
If you've ever been stung by a jellyfish, you'll easily understand about nematocysts.  I've been stung by one, but it was mild thankfully.  I was in the Gulf of Mexico.  The waters there are so warm!  But where we were, there were plenty of jellyfish.  They looked like clearish-white blobs, aimlessly floating around under the surface of the water.  We loved the warm water!  But didn't stay in long because of the jellyfish.  =(
Cnidarians do not all sting because of being touched.  Some will only sting because of a chemical reaction.
A jellyfish or a hydra will sting anything they touch.  A sea anemone (uh nim' uh nee)will only sting because of a chemical reaction.  For this reason, it will not sting a clownfish for example.  Remember in Finding Nemo, clownfish would live IN a sea anemone.
Click for a video of nematocysts firing.


Coral, Sea Anemone, Jellyfish


(4) p. 342-347, Phylum Annelida
This phylum is made up of worms.  There are quite a few kinds of worms, so many in fact, that this phylum is made up of only one type - the segmented worm.  A worm that looks as if it is in segments, or little sections.  An earthworm is perhaps the most common; at least it's what I think of when I think of a segmented worm.  Which I do not think of very often!  =)

An earthworm has an anterior end, and a posterior end.  The anterior end is where the mouth is, and is usually a little more pointed.  The clitellum is located nearer to this end.
The posterior end is where the, um... posterior is located!  =D
(Look back up at the bilateral symmetry of the crayfish to see "anterior" and "posterior."  
Also know that "dorsal" fins are on the backs of fish, because "dorsal" means back.)
Just looking at the parts of an earthworm makes one realize there is much more to the earthworm than one might think!  Again, I marvel at the Creator and His designs.  =)

I could not find a video that goes over the feeding habits of earthworms, or the respiratory, circulatory, and reproductive systems.
So I guess you'll have to study.  < gasp! >  =D
Writing down your vocabulary words as you go will help a lot.

Here's a video of a close up.  You can see the setae, which are little bristles.  You may have felt them before.  This is what an earthworm uses to help him move.


(5) p. 347b-350a, Experiment 11.3Earthworm Dissection
Earthworm Anatomy

After the dissection:
-Squirmin' Herman the Worm - review the parts, then do the quiz. (easy)
-See if you can label the parts of this worm. (a little harder)


(6) p. 350-352, Phylum Platyhelminthes:  The Planarian

Wow, planarians are really flat!

Planarians have bilateral symmetry.


(7) p. 352b-354, Phylum Nematoda
This phylum is made up of parasites.
The most common name for one parasite is ringworm.
Another is Trichinella spiralis, worms that live in the intestines of pigs and certain other game animals.  These can only be gotten rid of by extremely cold or extremely hot temperatures.  This is why it is important to practice careful handling of raw meat, and cooking it thoroughly.
In the Old Testament, there were certain laws that may seem drastic to us today.  They were not allowed to eat pork, for instance.
Leviticus 11:7 says, "And the swine, though he divide the hoof, and be clovenfooted, yet he cheweth not the cud; he is unclean to you." 
But these laws were for protection.  God knew that people then did not have the means we do today to ensure correct processing of meat.


(8) p. 354b-356, Phylum Mollusca
This phylum contains many organisms besides snails, such as clams, oysters, squid, etc.
Snails are a good example.
Study your textbook for the different parts of a snail, then watch the snail use its radula to eat lettuce.

Close-up view of the radula and foot.


  1. Who knew jellies got so huge!

  2. Thank you for posting these! I've been looking at your web site as I guide a HS class through Biology. The videos you use are some of the good videos available via the internet for free. During this module in particular, there was some beautifully created videos that were not correct. There are videos that make fun of creationists. So with that note, I will continue to tell parents that this blog provides good links/videos that state facts and not anti god agenda.


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