Science Lecture for Unit 12:Invertebrate Organisms
- Topic area: Biology, Invertebrate anatomy
- Terms and concepts to know: organs, organ systems, circulation, respiration, skeleton, muscles, sense perception, senses (touch, taste, smell, sight, hearing, balance!), growth and reproduction, digestion, endoskeleton, exoskeleton, sexual and assexual reproduction.
- See historical period(s): Classical Greece: Aristotle's Vertebrate and Invertebrate Biology
It is usually easier to compare and contrast groups of characteristics than to try to memorize isolated facts about new material. Look through the groupings below (systems, functions, similar anatomies) and make your own chart of the information. What details do you note that you would have missed otherwise?
We have already looked at the modern classification of groups of vertebrate animals (starting at the top of Aristotle's chart). Now we turn to the invertebrate animals, which are generally simpler in form and number of systems than vertebrates. The invertebrates include all the other multi-celled life forms which cannot make their own food. (Plants make their own food, and the protists and bacteria, which we look at later in the course, are single-celled life forms).
Most animals have systems of organs for different purposes. The most complex organisms (mammals) have up to ten such systems, which perform the following functions:
- circulation system - pumping fluids carrying oxygen and nutrients through the body (heart, blood vessels)
- respiration system - exchanging gases from waste for those needed for fuel production and consumption - (skin, lungs)
- integumentary system - surface protection (skin)
- skeletal system - internal support (skeleton and exo-skeletons)
- muscle system - movement (muscles)
- nervous system -communication, control, and sense perception (brain, nerves, ears, eyes, nose, mouth, skin)
- endocrine system - growth and development (hormones, glands)
- digestive system - breaking down nutrients (mouth, stomach, intestines)
- excretion system - getting rid of wastes(colon, liver, bladder, kidneys)
- reproductive system - make new little organisms (womb, eggs)
The modern classification systems group animals according to which possess these systems and by how complex the systems must be to support the life of the organism.
Study each of the invertebrate classes below, either through the associated web link or a biology text. Make notes of the organism's
- symmetry: This is the overall organization of the animal. If you draw a line through the animal, are the left and right sides mirror images of each other? Then the animal has bilateral symmetry. Some animals have radial symmetry: they have a ring-like structure.
- reproduction: Animals generally reproduce sexually, which requires two different organisms to exchange some materials (DNA). But some animals can reproduce by cloning or budding. Animals may give birth live (like mammals) or lay eggs.
- life cycle: This describes the different stages from birth through adolescence to maturity (when the animal is able to reproduce). Some animals require different environments for each stage--such as the amphibians we have already studied, which generally develop in water but spend adulthood on land. Insects and flatworms have complex life cycles.
- digestion: The digestive system has to be developed enough to support the animal on the available food supplies (since animals can't make their own food). One way to determine the complexity of the organism is to look at the number of organs involved in the digestive function.
- sensory organs: What sense organs does the animal possess? How complex is the nervous system that gathers the information and interprets it?
- special features not found in other groups: such as the mollusk's mantle
For example, the sponge, which is the simplest animal, reproduces both by budding (which does not require another sponge), and by a form of mating (which does require another sponge). It has no system of organs, so it has no stomach, mouth, or intestines, and no circulatory system. Each cell gets its nutrition directly from the water surrounding the sponge, or from the cell next to it. The sponge's life cycle is very simple: the new bud or ... swims freely for a short time, then fastens itself to a rock and procedes to grow and make little sponges until it dies. The sponge has no sense organs as such; it does expand and contract somewhat to force water through its internal cavity, so that it can filter the water for food.
The links below take you to a biologist's list of characteristics, and some of the terms are pretty technical. Don't worry about that. Concentrate on the major concepts -- what systems exist or are missing, what kind of symmetry occurs in the phylum, does the animal change shape during different phases of the life cycle, and so on.
Read through J. Kimball's summary of invertebrate animals (one page).
- The term duetostomes and protostomes is used do distinguish between animals with vertebrates or at least a notocord (echinoderms) and invertebrates. Which invertebrates belong to ecdysozoans? What characteristics do they share? How are they different from lophotrochozoans? Why are sponges and cnidarians not in either protostome group?
- Which is the most diverse group? (which has the most species)? Why do you think this group has so many different forms?
- Many invertebrates are "segmented". What advantages does this give an animal?
For each group, click on the left column name for more information.
Jellyfish, Hydras, Corals, Anemones
Flukes, Tapeworms, Planaria
| Round Worms
Clams, Mussels, Snails, Slugs, Squid, Octupus
| Segmented worms
Earthworms, Clams, Worms, Leeches
- Crustaceans: crayfish, lobster
- Insects: butterflies, ants
- Arachnids: spiders, ticks, scorpions
- Horseshoe Crabs
Sea stars, Brittle Stars, Sea Urchins, Sea Cucumbers
- How do invertebrates differ from vertebates?
- What characteristics in invertebrates are particularly useful for identification?
- Which classes of invertabrates are more adaptable to different habitats? Why?
- Which classes are successful (lots of species, lots of habitats, lots of individual organisms)? Why?
Further Study On your Own (Optional)
- The tree of life has a somewhat different organization of vertebrates and invertebrate animal forms.
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