- They lay eggs
- Invertebrates have no lungs, they respire through their skin.
- They have basically three body parts, Head, Thorax, Abdomen.
- They have no backbone
The three main types of Invertebrate skeletons:
- Hydrostatic skeletons - muscles surround a fluid-filled cavity that supports the muscles, when the muscle contracts, they push against fluid in the body cavity, causing the body to change its shape.
- Exoskeleton - external skeleton; a hard body covering made of chitin; move by straightening the joints (in arthropods)
- Endoskeleton - a structural support located inside the body; made of calcified plates; plates support and protect, the animal, and gives them a bumpy and irregular texture.
Invertebrates can be classified in 9 main categories, some of which are taxonomically obsolescent. All however are described in their own respective articles at the following
- Cnidaria (Corals, Sea Anemones and Jellyfish)
- Platyhelminthes (Flatworms)
- Nemathelminthes (Associated with Flatworms, but now is no longer a valid taxonomy. This was an obsolete phylum of Pseudocoelomate, as it was monophyletic)
- Annelida (Rigged worms, Sea worms, Earthworms)
- Arthropoda(Insects, Crustaceans and Arthropods)
- Echinodermata (Starfish, Squid and Octopus)