Simple InvertebratesChapter 15.1

Invertebrate Characteristics Invertebrates come in many shapes

and sizes Grasshoppers, clams, earthworms, and

jellyfish are examples of invertebrates They are all very different from each

other. Invertebrates have 3 different body

plans or types of symmetry Bilateral Symmetry Radial Symmetry Asymmetry

White Board Activity Using a White board and your

marker draw a picture to represent Bilateral symmetry Radial symmetry Asymmetry

Share with your table groups when you are done

Neurons and Ganglia All animals except sponges have

special tissues that make fibers called neurons. Neurons carry messages around the

body to control an animal’s actions. Simple invertebrates have neurons

arranged in networks or nerve cords. Nerve cords are packs of neurons that

carry messages along a single path.

In some invertebrates many nerve cells come together as ganglia (singular, ganglion). A ganglion is a concentrated mass of

nerve cells. Each ganglion controls different parts

of the body. Ganglion are connected by a nerve

cord In complex invertebrates, ganglia are

controlled by a brain.

Guts Almost all animals digest food in a

gut. A gut is a pouch within cells that

releases chemicals that break down food into small particles. The cells in the gut then absorb the food

particles . In complex animals, the gut is inside

the coelum, a coelum is the body cavity that surrounds the gut. The coelum contains many organs like the heart and lungs. This makes sure that the movement of the gut doesn’t disturb other organs

Sponges Sponges are the simplest

invertebrates They are asymmetrical and have no

tissues, gut or neurons. Adult sponges move only millimeters

per day if they move at all. The only reason sponges are

classified as animals is because they are unable to make their own food.

How do sponges eat? Sponges feed on tiny plants and

animals. Because they cannot move they seep

water into their bodies through their pores. This water brings oxygen and food into their body. Pores are holes on the outside of the

sponges body. Special cells called collar cells line

the cavity. They filter and digest the food.

Water leaves the body through the hole at the top called the osculum.

Sponge body part abilities Sponges have some special abilities

If you forced a sponges body through a strainer, the separated cells could come back together again and form a new sponge.

If part of a sponge is broken off, the missing part can regenerate, or grow back.

Sponges reproduce through regeneration and also sexual reproduction

Kinds of sponges All sponges live in water, most live in

the ocean Sponges come in many different shapes

and sizes. Most sponges have spicules, which are fibers that make up the sponges skeleton.

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Cnidarians Cnidarians are a group of

invertebrates that have stinging cells. Jellyfish are members of this group They are more complex than

sponges. They have complex tissues and a gut for digesting food. They also have a simple nervous system

If a piece of cnidarian is broken off it can form a new cnidarian

There are 2 different body forms The Medusa: this type will swim

through the water The Polyp: they usually attach to a

surface. All cnidarians have radial symmetry

Stinging Cells All cnidarians have tentacles covered

with stinging cells When another organism presses

against the stinging cells the cnidarian uses water pressure to fire tiny barbed spears from each cell.

Kinds of cnidarians There are 3 major classes of

cnidarians Hydrozoans: spend most of their lives

as polyps and live in both fresh and sea water

Jellyfish: catch their food in their tentacles and spend most of their lives as medusas

Sea anemone’s and corals: spend their lives as polyps and are often brightly colored

Flat worms There are many different kinds of

worms, not all are round like an earthworm.

Flatworms are divided into three major classes Planarians and marine flat worms Flukes Tapeworms

All flatworms have bilateral symmetry, most also have defined heads and 2 large eyespots

Some flatworms also have bumps on the side of their heads called sensory bumps

Planarians Live in freshwater or on land in damp

places They eat other animals or parts of

other animals and digest their food in their gut

Planarians use their sensory lobes to help find food and they even have a brain

Flukes Are parasites Most live and reproduce in the

bodies of another animal. Their fertilized eggs pass out of the

body with the waste and are then ingested by other animals.

They have tiny heads without eye spots or lobes and use suckers and hooks to attach to the other animals.

Tapeworms Are similar to flukes They have a small head, no eyespots

or sensory lobes They do not have a gut.

They attach to another organisms gut and absorb the nutrients from that organism

Roundworms Have bodies that are long, slim and

round like spaghetti The have bilateral symmetry They also have a simple nervous

system with a ring of ganglia making up their simple brain. Parallel nerve cords connect the 2 ends of their body

Most round worms are tiny, breaking down the dead tissue of plants and animals making the soil rich.

Some round worms are parasites like Trichinella spiralis.