Invertebrate Animals BEN218

Learn about Invertebrate Animals

Invertebrates include a great diversity of animals, many of which often go unnoticed; either because they are too small to see, or live in places where they are not commonly seen, such as in the soil, as parasites inside plants or other animals, or under the water in rivers, lakes or oceans.


Course Structure

1. Scope and Nature of Invertebrate Animals

  • Introduction
  • Significance to humans
  • Comparative studies - invertebrate animals
  • Important terminology
  • Overview of Invertebrate Phyla
  • Microscopic phyla -Tardigrada, Kinorhyncha, Loricifera, Placozoa
  • Worms - Acanthocephala, Annelida, Hemichordata, etc
  • Corals and relatives - Cnidaria, Ctenophora, Ectoprocta, Porifera
  • Echinoderms and Molluscs  - Echinodermata, Mollusca,  Brachiopoda
  • Complex Invertebrates - Arthropoda

2. Microscopic Animals

  • Protozoa or Animalia
  • Phylum Nematoda
  • Mites
  • Phylum Tardigrada
  • Adaptability and Survival
  • Anhydrobiosis
  • Cysts
  • Phylum Kinorhycha
  • Phylum Loricifera
  • Phylum Placozoa

3. Worms & Worm Like Animals

  • True worms vs Worm like organisms
  • Worm evolution
  • Bilateral symmetry
  • Cephalisation
  • Body organisation
  • Characteristics and systems showing complexity
  • Phylum Platyhelminthes (Flatworms)
  • Free living flatworms
  • Parasitic flatworms
  • Significance to Humans - Liver fluke, blood flukes, tapeworms
  • Beef tapeworm
  • Phylum Nematoda (Roundworms)
  • Phylum Annelida (Segmented Worms)
  • Other Worm Like Animals - Acorn worms, ribbon worms, Spiny headed worms, etc.
  • Coelomate Worms

4. Sponges, Corals, Anemones, Jellyfish

  • Introduction
  • Phylum Cnidaria
  • Hydrozoa
  • Scyphozoa
  • Cubozoa
  • Anthozoa
  • Cnidaria and Humans
  • Phylum Ctenophora
  • Phylum Porifera - Location, Internal & External Structures, Reproduction, Toxicity
  • Classes within Porifera
  • Finding food 
5. Molluscs and Echinoderms
  • Phylum Echinodermata
  • Crinoidea - Sea Lilies and Feather Stars
  • Ophiuroidea -Brittle stars, Basket  Stars
  • Asteroidea - Sea stars or Starfish
  • Case Study - Crown of Thorns Starfish
  • Echinoidea -Sea urchins, Heart urchins, Sea dollars
  • Chass Holothuroidea - Sea Cucumbers
  • Phylum Mollusca - general characteristics and types 

6. Arthropods 1

  • Classification into Arachnida, Crustacea, Myriapoda and Insecta (insects)
  • Origin
  • Terminology
  • Characteristic body parts
  • Ecdysis
  • Digestion, Respiration, reproduction and other systems
  • Phylum Arthropoda
  • Chelicerata (Chelicerates)
  • Arachnida (Scorpions, Spiders, Mites and Ticks)
  • Scorpiones (Scorpions) 
  • Araneae (Spiders) 
  • Acari (Mites and Ticks) 
  • Opiliones (Daddy Long-Legs)
  • Merostomata (Horseshoe crabs) 
  • Pycnogonida (Sea spiders) 

7. Arthropods 2

  • Terminology
  • Crustacea (Crustaceans)
  • Class Malacostraca -Crayfish, Crabs, Shrimp etc
  • Branchiopoda - Fairy shrimp, Water fleas
  • Cephalocardia 
  • Remipedia
  • Maxilopoda
  • Sessile Crustaceans
  • Sub Phylum Uniramia - millipedes, centipedes and insects
8. Insects 1
  • Origin of insects - winged vs non winged
  • Class Entogantha -Collembola, Diplura, Protura
  • Class Insecta
  • Insect features
  • Mouthparts
  • Insect classification into 29 orders
  • Specialised organs
  • Reproduction
  • Lifecycle
  • Senses - vision, communication
  • Odonata -Dragonflies and Damselflies
  • Mantodea - Mantises
  • Orthoptera - Grasshoppers, Crickets, Katydids

9. Insects 2

  • Significance to man 
  • Clean air and water
  • Pollination by insects
  • Edible insects
  • Case Study - Grasshoppers save lives
  • Order Diptera - Mosquitos and Flies
  • Order Hymentoptera - Bees, wasps, ants, sawflies
  • Order Coleoptera - Beetles, weevils



Some types of animals that occur in the microscopic world belong to taxonomic groups that are not represented in the visible world; but others (e.g. arachnids and worms) are animals that have both large visible representatives, as well as tiny microscopic representatives. Many of these microscopic animals are found in aquatic habitats, where they feed on algae and organic detritus. They play an important role in the carbon cycle of our oceans and water bodies, recycling organic matter and providing food sources for animals higher up the food chain.  They also display fascinating anatomies and biological processes, uniquely adapted to the biological niche they occupy. Their body structures and unique biological processes may also provide insights in evolutionary biology, and the early stages of life on earth.

Examples of microscopic animals:


Nematodes are worms. They live in water (fresh or salt water) or on the land (from polar regions to deserts and even in hot springs). Some can be visible to the naked eye, but most are tiny (e.g. a handful of soil may contain thousands of nematodes). Several species of nematodes also spread plant viruses they do this by feeding on the tissue of infected plant roots and then move on to healthy plants infecting them as a result. Those that transmit viruses in plants fall mainly within the families: 

  • Longidorus (needle nematodes): accumulate around and under roots tips of plants causing damage to plants and crops e.g. cause damage to corn and mint etc. also spreads tobacco, tomato and raspberry ringspot viruses some species. 
  • Trichidorus (stubby root nematode): soil dwellers that feed on plants; diseases include pea early browning virus.
  • Xiphinema (dagger nematode): feed on the roots of plants and crops and also spreads viral mosaic and wilting diseases and spreads tobacco, tomato and raspberry ringspot viruses.


Mites are tiny insects related to spiders (but distinct from spiders) and include ticks. Some are too small for the naked eye to see. Although highly variable in appearance they have four pairs of legs and two body segments and are usually without eyes (but may also have from 1 to 5 eyes depending on the species) and without wings. 

There are some 50,000 species of mites which may be useful or destructive; they live on every single continent in the world and in any environment: within the soil, on surfaces, on people, animals, on plants, in water in household furnishings including mattresses, curtains, carpet and bedding etc. Mites can cause skin and other allergies and respiratory problems in humans (about 65 known species) and other animals. 

Mites are also significant part of the ecosystem they help to decay dead plant materials, other organic matter and algae, bacteria, fungi, mosses and yeasts. Although mites (e.g. spider mites) are a significant pest on plants and agricultural crops some species (e.g. phytoseiid mites) have symbiotic associations with certain plant species (on which they live) making them useful in biological pest control of other mites. 


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