Comparing Living Things Science Unit A – Chapter 1 Comparing Living Things

Lesson 3: How Are Animals Classified?

Animals Without Backbones Animals that have no backbones are called invertebrates. Invertebrates are many-celled organisms. Sponges, jellyfish, worms, sea stars, mollusks, and arthropods are all examples of invertebrates.

Sponges Look more like plants than animals Live underwater Do not move -- They attach themselves to rocks or other objects in the water. Trap and eat tiny organisms that float in the water that flows in and out of their hollow bodies

Jellyfish Have hollow bodies that water flows in and out of Have a mouth surrounded by tentacles Tentacles are used to capture prey.

Mollusks Have soft bodies Bodies are protected by one or two shells. We eat many of these. Snails, oysters, and clams are examples of mollusks.

Sea Stars Live on the ocean floor Use suction cups on their underside to stay in place and to pry open shells Tough skin and spines protect them from enemies.

Arthropods This groups contains more than 80% of all animal species! Lobsters, crabs, spiders, centipedes, millipedes, and insects (70%) are examples. Have a stiff outer covering called an exoskeleton for protection. The exoskeleton has joints that allow movement.

Worms Live mostly underground Eat the remains of dead plants and animals Have narrow, tubelike bodies Flatworms have flat bodies. Roundworms look like tiny snakes with no heads. Earthworms are examples of segmented worms.

Animals With Backbones Animals that have backbones are called vertebrates. There are five groups of vertebrates. Fish Amphibians Reptiles Birds Mammals

Fish Live their whole lives in the water Use tails and fins to move Take in oxygen from the water through their gills Lay eggs in water Range in size from 1 inch to 50 feet long

Amphibians Lay eggs in water Live part of their lives in water (with gills) and part on land (with lungs) Usually stay near water Frogs and salamanders are examples.

Reptiles Breathe with lungs their whole lives Bodies are covered with tough, dry scales. Most lay leathery-shelled eggs on land. Lizards, snakes, turtles, alligators, and crocodiles are examples.

Birds Breathe air all their lives Lay hard-shelled eggs on land Hollow bones make their bodies light. Bodies are covered with feathers. Not all birds fly!

Mammals Have hair or fur on their bodies Breathe through lungs all their lives Mammals are the only animals that feed their young with milk produced by the mother. Mammals give birth to live young. Live on land, in water, and in the air

Questions What are invertebrates? What are vertebrates?