Invertebrate Characteristics• They are all very different from each other• Examples: jellyfish, clams, earthworms, grasshoppers• Have 3 different basic body plans, or types of symmetry• Can be bilateral, radial, or asymmetry (no symmetry at all)
Bilateral: the two sides of its body mirror each other. Radial: Its body is organized around the center, like spokes on a Asymmetrical: cannot wheel draw a straight line todivide its body into two or more equal parts. Its body is not organized around a center.
Neurons and Ganglia• All animals except sponges have special tissues that make fibers called neurons, which allow animals to sense their environment• Neurons also carry messages around the body to control animal’s actions• Simple invertebrates have neurons arranged into a nerve cord• In some, many nerve cells come together as ganglia
• Each ganglion controls different parts ofthe body•Ganglia are controlled by the brain
• Gut: pouch lined with cells that release chemicals that break down food into small particles• In complex animals, gut is inside a coelom• Coelom: body cavity that surrounds the gut and contains many organs, such as the heart and lungs (but kept separate)• Keeps gut movement from disturbing other body processes
• Sponges cannot move and do not have gut• A sponge sweeps water into its body through its pores• Water flows into cavity in the middle of the body, bringing oxygen and food• Special cells called collar cells line the cavity and filter and digest food
• Water leaves the body through a hole in the top of the sponge called the osculum• Sponges have unusual abilities—if you force it through a strainer, the parts come back together and reform a sponge —called regeneration.
• A sponge’s skeleton supports its body and helps protect it from predators• Most sponges have skeleton made of small, hard fibers called spicules – Some are straight, curved, or have complex star shapes• Sponges are divided into groups based on kind of skeleton it has
• Cnidarians – Invertebrates with stinging cells – Just like sponges, if the body cells are separated, they can come back together to re-form the cnidarian – Two body forms • Medusa: swim through water • Polyps: usually attach to surface
• All cnidarians have tentacles covered with stinging cells• When an organism brushes against the tentacles, it activates hundreds of stinging cells• Each stinging cell uses water pressure to fire a tiny, barbed spear into the organism• The tiny spears can release a painful—and sometimes paralyzing—poison into their targets
• Cnidarians use their stinging cells to protect themselves and to catch food
1. Hydrozoans: spend entire life as polyp2. Jellyfish: spend of life as medusas, and catch food in tentacles3. Sea anemones and corals: 1. Spend their lives as polyps 2. Often brightly colored
• Simplest worms are flatworms Flatworms• All flatworms have bilateral symmetry• Many have a clearly defined head and two large eyespots (can sense direction of light)• Some have bumps on side of head called “sensory lobes”, used for detecting food• Three major classes: – Planarians and marine flatworms – Flukes – Tapeworms
• Planarians – Life in freshwater lakes and streams – Most are predators – Its head, eyespots, and sensory lobes are clues that it has a well-developed nervous system
• Flukes – Parasites – Most live and reproduce into bodies of other animals – Flukes have tiny heads without eyespots or sensory lobes – Have special suckers and hooks for attaching to animals
• Tapeworms – Small head with no eyespots or sensory lobes – Live and reproduce in other animals – Feed on these animals as parasites – Tapeworms do not have a gut—they just attach to intestines of another animal and absorb nutrients
Roundworms• Have long, slim, round bodies (bilateral symmetry) and a simple nervous system• Most species are very small: a single rotten apple could contain 100,000 roundworms!• Some break down dead material, others are parasites• One roundworm causes the disease trichinosis
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