Animals without backbones Grade 4 invertebrates Invertebrates do not have a backbone Most animals on Earth do not have backbones Symmetry when two parts of an object are identical along an imaginary dividing line ID: 773320
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Animals without backbones Grade 4
invertebrates Invertebrates do not have a backbone. Most animals on Earth do not have backbones! Symmetry: when two parts of an object are identical along an imaginary dividing line. For example, this shape can be divided along a midline:
Aquatic invertebrates Aquatic animals live in the water Many animals that live in water are invertebrates Sponges: the simplest invertebrates. Made up of two cell layers. Shaped like a sack with an opening. Do not have symmetryCnidarians: have tentacles, which are arm-like limbs with stinging cells on the end. Some stay in one place while others swim.
sponges
Coral and sponges
Mollusks and echinoderms Mollusks: All have shells Most have shells outside the body and stay in one placeSome have shells inside the body and moveEchinoderms: Have spiny skinHave endoskeletonEndoskeleton: internal support structure
Mollusks that move
Mollusks that stay in one place
echinoderms
arthropods Largest group of invertebrates They have: Jointed legsBody divided into sectionsExoskeleton Hard covering that protects the bodyKeeps moisture inExamples are lobsters, bees, insects, spiders
Insects and centipedes Insects One pair of antennae Three pairs of legsOne or two pairs of wingsThree body sections Centipedes and millipedesLong slender bodies and many legsCentipede: one pair of legs on each sectionMillipede : two pairs of legs on each section
Arachnids and crustaceans Arachnids: Four to five pairs of legsTwo body sectionsFangs Examples: spiders, ticks scorpionsCrustaceans:Two pairs of antennaeTwo or three body sectionsAbility to chewMost live in the oceansExamples: shrimp, crabs, lobster
Some crustaceans
Centipedes and millipedes
Some insects
worms Three types: Flatworms FlatThree cell layers thickSome live inside other animals One opening for food and wastesRoundwormsRoundOne –way digestive systemMost live inside the bodies of other animalsSegmented worms RoundBodies have segments, or sectionsSeparate opening to get rid of wasteLive on land; none live in another animal’s body