7Invertebrates

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.

The fi rst family we wi l l look at is cal led “Pori fera.” (pronounced: por- i f-ur-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?

The next invertebrate group we wil l look at is the Cnidarians family (pronounced: nie-dare-ee-uns Note: the init ial ‘c’ is s i lent).

This family has two groups. One contains the anemones and corals (c lassifi ed as “Anthozoa” - the name comes from the Greek words ánthos – “fl ower” and zóa - "animals", hence anthozoa = "fl ower animals,“ which fi ts them well because of their fl ower- l ike appearance.)

The other members of the Cnidarians family are the jel ly fi sh.

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 (pronounced: ee-kine-oa-derms ) .

The word “echinoderm” means “spiny skinned.” Many echinoderms are covered with spines.

Most adults are easy to recognize because of their fi ve-point, radial symmetry, which means many Echinoderms look the same on both sides when cut in half.

This class includes familiar animals like sea stars, sea urchins, sand dollars, and sea cucumbers.

Echinoderms are often recognizedbecause 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?

Snails, slugs, clams, oysters, octopus, and squid are all part of the next group of invertebrates we wil l look at. What is similar about the bodies of these animals?

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 sophisticatednervous 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 givesyou an idea of how large that squidwould look alongside an adultscuba 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 byhumans include using theshells to trade as a form of currency, harvesting pearlsfrom 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.

Worms are the fi fth c lass o f inver tebrates we’ l l ta lk about .

Worms have long , tube- l i ke bod ies and no legs .

Worms can be mic roscop ic (very smal l ! ) ; they can a l so be as long as a meter s t i ck!

They l i ve in var ious p laces—oceans ,f resh water , on land , on p lants , andeven in an imals .

Where have you seen worms?

The last c lass of invertebrates we wi l l ta lk about are the Arthropods (pronounced: ar- throw-pods) . Th is is the largest group of invertebrates, and you see members of th is fami ly near ly every day. Arachnids (sp iders and scorp ions) , insects , and crustaceans are a l l part of th is fami ly.

The main character ist ics of th is fami ly is that they general ly have exoskeletons (ske letons on the outs ide of the i r bodies) , jo inted legs, and segmented bodies.

Have you ever seen a crab? Crabs have a hard shel l on the outs ide. This exoskeleton protects the soft ins ides of the i r bodies.

Can you th ink of any insects that have hard cover ings on the outs ide of the i r bodies?

Look closely at the legs of this ant. Can you see how they have several places where the legs bend? They have six jointed legs.

And what do you notice about the

shape of i ts body?

How are the bodies of Arthropods the same as your body?

How are they diff erent?

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 fami ly contains some unique and excit ing animals! Be on the lookout for invertebrates this week – you should fi nd quite a few. Remember, they outnumber vertebrates, inc luding us, 9 to 1!