Simple invertebrates
Transcript of Simple invertebrates
The Good, The Bad, and the Spineless
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)
Asymmetrical: cannot draw a straight line to
divide its body into two or more equal parts. Its body is not organized
around a center.
Bilateral: the two sides of its body mirror each other.
Radial: Its body is
organized around the center, like
spokes on a wheel
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 of the 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
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• 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 polyp
2. Jellyfish: spend of life as medusas, and catch food in tentacles
3. Sea anemones and corals: 1. Spend their lives as
polyps2. Often brightly colored
Flatworms• Simplest worms are
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