Ch 15:

Invertebrates

G8 SAT/AP

Ms. Isra Abu Younis

How we classify animals?

• Animals have many things in common.

• They also have many things that are different.

• These features can be used to classify animals.

The Nature of Animals (Kingdom Animalia)

• Invertebrates ( animals with no backbones)= 95% of all animals

• Vertebrate an animal with a backbone (5% of animals)

- Vertebrata is a subphylum of the phylum Chordata

- Vertebra one of the repeating bony units of the backbone

Invertebrate Phyla

1. Sponges

2. Cnidarians

3. Flatworms

4. Roundworms

5. Segmented Worms

6. Mollusks

7. Arthropods

8. Echinoderms

Body plans

• Invertebrates have two basic body plans, or types of symmetry.

• Animal Body Symmetry - the way body parts are arranged around a center point.

• The body parts match up around a midpoint or line.

• Some animals have no symmetry.

• We can use symmetry to classify animals

1. Asymmetry

2. Bilateral Symmetry

3. Radial Symmetry

Asymmetry = animal without symmetry

Sponges have no symmetry

Bilateral and Radial Symmetry

• Bilateral symmetry : a body with two similar halves

• Radial Symmetry: the body parts are arranged in circle around a center point.

Nerves system

• Sponges are the only multicellular animals without a nervous system

• Nerves that carry signals to control the movements of the body

• Simple invertebrates have nerves arranged in networks or in nerve cords throughout their body

• Ganglia : dozen of nerve cells come together in groups, they control different body parts

• Complex animals have a brain and head

Digestive system

• Almost all animals digest food in a central gut

• Gut : is a pouch lined with cells that release powerful enzymes to break down the food into small particles that cells can then absorb.

• Coelom : a special space in the body for the gut in complex animals. It allows the gut to move the food without interference from the movement of the body. Organs such as the heart and the lungs also in the coelom.

*Acoelomates

*Pseudocoelomates

*Coelomates

Sponges

• The simplest animals

• They have : no symmetry , no head , no nerve and no gut

• Live in water , most are found in the ocean

• Absorb and digest food through their bodies by collar cells

• They produce egg and sperm so they are neither male or female

• They regenerate which means a new sponge will grow back when a piece is broken off

• Most sponge have a skeleton made of needlelike splinters called spicules . It supports the body and helps protect it from predators.

Cnidarians

• Cnidaria : (Greek) = a stinging thread

• They have complex tissue , gut for digestion food and nervous system

• They can regenerate

• This phylum includes some 10,000 species like: Sea anemones, corals, jellyfish, Hydra and Portuguese-man-of-war.

• Have arm-like parts called tentacles

• Stinging cells at the end of each tentacle

• Stun prey

• Two body forms: Polyp vs medusa

Flatworms

• Their body is flat and thin

• They have bilateral symmetry

• They have a head and a tail

• Most do not hurt other living things

• Example : Planarians figure 9+10

• Some live inside other animals. Parasites, like tapeworms. Figure 12

Roundworms

• They are round, long and slender

• They have bilateral symmetry

• Most of them are tiny

• They help build rich soil by break down the dead tissue of plant s and animals

• They have simple nervous system. A ring of ganglia forms a primitive brain, and parallel nerve cords run the length of their body.

• Most of them are parasites that live inside other

animals.

• They include : pinworms and hookworms

Segmented worms

• Bodies are divided into parts, or segments.

• The parts are the same, except for the head and tail ends.

• Each has an opening for the digestive system.

• Most live on land

• They do NOT live inside other animals.

• Earthworms, sandworms, and leeches are segmented worms.

Quick Check

• Write the letter for the fact about each worm.

• ______flatworms

• ______ segmented worms

• ______ roundworms

• A. thin bodies with pointed ends

• B. do not live in other animals

• C. simplest kind of worms

Mollusks• Have a shell

• Some have shells inside the body

• Most live in water

• Some swim

• Others stay in one place

• Body divided into 3 parts

» Head

» Body

» Foot

• There are over 112,000 species of mollusks

Mollusks

1. Snails and slugs are the largest group of mollusks

• Snails have a hard shell

• Slugs do not have a shell

2. Clams, Scallops and oysters are also a group

– They have hinged shells that open and close

3. Squids and octopus don’t have outer shells

– They can swim fast to catch their prey

Echinoderms

• Spiny skin

• Have a support structure inside the body called an endoskeleton (means inside the body)

• Have radial symmetry

• Have tube feet which can attach firmly to surfaces

• Tube feet allow them to move around

• Simple nervous system consisting of a nerve ring and a radial nerves.

• Sea stars (starfish ), sea urchins, sand dollars and sea cucumbers

What are arthropods?

• The largest group of invertebrates is the arthropod group. They make up ¾ of all animals

• Arthropods have legs that bend. Their bodies have sections.

• Some breathe with gills and others through tubes.

• Every arthropod has an exoskeleton. This is a hard covering on the outside of the body.

• ALL arthropods have 3 things in common

• Jointed legs

• most have antennae

• body with external skeleton

ARTHROPODS

• Crustaceans: crabs, lobsters and crayfish

• Arachnids: spiders, scorpions, ticks and

mites

• Centipedes

• Millipedes

• Insects : mosquitoes, flies , ants, beetles