Ch9L2: Invertebrates

Chapter 9 Lesson 2

Invertebrates

What is an invertebrate?

• Animals without backbones.

• Most support their bodies with either a hydrostatic skeleton (fluid-filled internal cavity) or an exoskeleton (a hard outer covering) only some have endoskeletons.

• Some are parasites - animals that survive by living inside or on another organism (do not help the other organisms survival)

• They have many adaptations for survival.

Sponges

• The oldest branch in the animal family tree, phylum Porifera.

• Called simple animals as they have only a few types of cells and no true tissue.

• They cannot move and are attached to rocks and other underwater structures.

• They have tiny, stiff fibers that support their bodies.

Cnidarians

• Corals, anemones, jellyfish, hydras and Portuguese man-of-war are members of phylum Cnidaria.

• The name comes from the special cells these animals use to catch their prey.

• Nematocyst cells inject poison into animals that they touch.

• They do have true tissues, some swim and move, others attach to rocks like the sponges.

Flatworms

• In the phylum Platyhelminthes, it's name accurately describes it.

• They have bilateral symmetry and a flat body shape.

• Most live in fresh water or salt water.

• Some swim freely, gathering food in the water, others are parasites that can infect humans.

Segmented Worms

• Worms in the phylum Annelida have a body that looks like a tube of rings.

• Each segment is a fluid-filled compartment, meaning they have hydrostatic skeletons.

• They also have tiny, stiff hairs called setae that helps them grip surfaces.

• Segmented worms can be parasites, like leeches, or live in the soil like earthworms.

Mollusks

• Snails, slugs, octopuses and oysters are all part of the phylum Mollusca.

• Most mollusks have a footlike muscle that is used to move.

• They also have a mantle, a thin layer of tissue that covers their internal organs.

• A mollusks shell supports and protects their body.

• Slugs have no shells, squids have internal shells.

Roundworms

• Nematodes, or roundworms, are part of the phylum Nematoda.

• Some can infect humans, other infect dogs or even plants.

• Most live in soils and are too small to see.

• They have a hydrostatic skeleton and a hard outer covering called a cuticle for protection.

• They shed their cuticle to replace it with a larger one in a process called molting.

Arthropods

• There are more animals in the phylum Arthropoda than in all the others combined.

• They have bilateral symmetry, a hard outer covering that it must molt in order to grow, and exoskeletons for protection and movement..

• Their bodies have 3 parts: head (sense organs), thorax (where the legs are), abdomen (contains intestines)

Insects

• Most arthropods are insects.

• Scientists call them hexapods as they have 6 legs.

• Insects are the only arthropods that can fly.

• They also go through metamorphosis - the body form changes as it grows from an egg to an adult. i.e. caterpillar=butterfly

Other Arthropods

• There are 3 other major groups:

• Spiders and scorpions - they have 8 legs used to walk and grab stuff

• Crabs and lobsters - mostly live in water, have 3 or more pairs of legs

• Centipedes and millipedes - they have the most appendages (legs)

Echinoderms

• Echinoderm means spiky skin, they are from the phylum Echinodermata.

• It feels spiky because of the hard enoskeleton just beneath its thin skin.

• They all live in salt water and move slowly with suction feet.

• They start with bilateral symmetry when young and develop radial symmetry later.

Multiple Choice

Which characteristic is common to all invertebrates?

• backbone

• mantle

• cell walls

• no backbone