Invertebrates• Most animals in the world are invertebrates

• These are animal without a backbone

Groups

The most common groups of Invertebrates are:1. Arthropods2. Protozoa3. Annelids4. Echinoderms5. Mollusks

Many invertebrates have a fluid filled skeleton, likea worm or a jellyfish.Others have a hard outer shell like crustaceans (crabs)and insects (spiders).

ArthropodsArthropods include:

• Insects

• Arachnids

• Crustaceans

Arthropods: Insects• Insects are the largest group of arthropods.

• They are very adaptable which means they can live almost anywhere in the world.

• They have an exoskeleton which serves mainly as a protective covering.

• An insects body consists of 3 parts: head, thorax and abdomen

Arthropods: InsectsMore characteristics of insects:• pair of antennae• compound eyes• have legs• some have wings

Compound eyes in the head of a crane fly

ArachnidsCharacteristics:• spiders, scorpions, ticks and mites• do NOT have antennae• exoskeleton• have many legs• scorpions are the largest arachnid group

spider scorpion tick mites

CrustaceansCharacteristics:• Most common are the crab, lobster and barnacle• Live mostly in the ocean or other waters• Have a hard, external shell that protects their body• Have a head and abdomen• Their head has antennae• Have legs• Some have claws

crab lobster barnacle

Protozoa• Protozoa are single celled animals• Most are extremely tiny (microscopic)• consume(eat) bacteria• Two main types: amoebas, flagellates

flagellate

amoeba

Annelids• Annelids have bodies that are divided into segments (parts).• They have bristles (like legs). Some have short ones (earthworms) others have long ones.• They have very well-developed internal organs, so it’s easy for them to move around on the ground.• There are about 9,000 of known annelids.• lugworms, clam worms, bristle worms, fire worms, sea mice

Echinoderms• These animals live in the ocean• They have arms or spines that start at the center of their body• The center part of their body contains their organs and their mouth• The spines often protect them from predators• Examples are: star fish (sea stars), sea urchins, sea cucumbers

Sea urchin Sea stars

Sea cucumber

Mollusks• Most mollusks have a soft sin-like organ on the inside and a hard shell on the outside• Some mollusks live on land and others in the water• Examples of mollusks that live on land:• snails and slugs• Examples of mollusks that live in the water:• oyster, mussel, clam, squid, octopus

oyster mussel clam squid octopus

Mollusks

• Land mollusks have a soft “foot” that helps them move—but they move very slowly• Water mollusks propel themselves in the water by ejecting water from their bodies• Some mollusks, like the oyster, attach themselves to rocks and Feed from the food particles