Invertebrate Investigation

Invertebrates, or animals without a backbone, make up 97% of the animals in the world. They are literally everywhere; in a pond, under a log, in the soil, on a sandy beach, in our homes, climbing trees, on a flower…not hard to find. They come in various shapes and sizes. This module will briefly discuss various classes of organisms that belong in the invertebrate group, their special characteristics and where they can be found.

What are Invertebrates?

-         with no backbone

-         multicellular

-         No cell walls

-         Reproduce by 2 reproductive cells coming together

This includes:

Protista - unicellular organism; need microscope to see

Insects – beetles, flies, ants, bees and true bugs, butterflies, moths and skippers

Annelids – segmented worms

Molluscs – clams and mussels, snails and slugs

Echinoderm – marine animals; starfish, brittle stars, sea urchins, sand dollars, sea cucumber

Crustaceans – crabs, lobster, crayfish, shrimp, krill and barnacles

Arachnids – spiders, ticks and mites



  • mostly unicellular; some are multicellular (algae)
  • can be heterotrophic or autotrophic
  • most live in water
  • all are eukaryotic (have a nucleus)
  • not a plant, animal or fungus


  • have chitinous exoskeleton
  • 3 part body: head, thorax and abdomen
  • 3 pair of jointed legs
  • Compound eye
  • Two antennae

In the Pollination modules, bees, wasps and flies were discussed. Click here for more information.

Butterflies and moths are an example of insects. They have 6 jointed legs, 3 body parts (head, thorax and abdomen), a pair of antennae, compound eyes and an exoskeleton; all characteristics of insects. Butterflies and moths are the only insects with large scaly wings. These four wings are attached to thorax. Their bodies are covered in tiny sensory hairs. The optimal body temperature of butterflies for flight is 27°C to 39°C, although they can fly at 13°C, but more energy is required.

Moths vs. Butterflies



active at night (nocturnal)

during the day (diurnal)

dull colours

bright colours

antennas are feather-like

antennas are straight with knobs

cocoon are buried under leaves

chrysalises – hang from leaves

wings are spread out when resting

wings are folded when at rest

caterpillar are hairy

pupa are hairless


  • long cylindrical shaped bodies made up of similar segments
  • no appendages
  • no antennae
  • no obvious head end

Earthworms fit the four characteristics listed above, therefore they are annelids. They are considered highly beneficial organisms. As the tunnel through the ground feeding, they ingest a huge amount of soil, speeding up the nutrient cycle and increase productivity. While burrowing they aerate soil allowing rainwater to penetrate deeper into the ground.


  • soft-bodied animal
  • no segmentation
  • often have an external shell made of calcareous material

Snails and slugs (Gastropods), and clams and mussels (Bivalves) are all molluscs. They all have soft-bodies with no segmentation. Clam, mussels and snails all have external shells. Can you think of any other molluscs? Head to the beach and see what you can find.


  • marine animals
  • most have arms or spines that radiate from the centre of their bodies
  • central body contains organs and mouth for feeding

Sea urchins, sea stars and sand dollars are all echinoderms. Sea stars, aka starfish, have small tube feet to help with movement and feeding. Their mouth is located on the underneath, which allows them to eat clams and mussels.


  • have an exoskeleton
  • live in the ocean or other waters
  • have a head and abdomen
  • head has antennae
  • abdomen has heart, digestive system and reproductive system; appendages: leg sometime with claws

Lobster, crabs, crayfish and barnacles are all crustaceans.


  • exoskeleton
  • jointed appendages
  • 4 pairs of legs; some cases where first pair are modified for feeding on and holding prey
  • No antennae or wings

Spiders, mites and ticks are member of the Arachnids class. Spiders have eight legs used for walking. The first pair is used for holding prey and feeding. Some use the second to hold and kill prey. Most spiders have eight eyes and fangs that inject poison, paralyzing their prey. Many spiders have the ability to produce silk and spin webs.

Now that you have been introduced to all the classes of invertebrates go try to find some!

For more information check out the links below:

Biology4kids- Invertebrates


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