What types of animals lack a backbone?

Animals that lack a backbone are called invertebrates. This is a huge and diverse group, comprising over 95% of all animal species! Here's a breakdown of some major invertebrate groups:

1. Porifera (Sponges)

* Simple, filter-feeding animals with no true tissues or organs.

* Examples: bath sponges, glass sponges

2. Cnidaria (Jellyfish, Corals, Anemones)

* Radial symmetry, stinging cells called nematocysts.

* Examples: jellyfish, sea anemones, corals

3. Platyhelminthes (Flatworms)

* Bilateral symmetry, flat bodies.

* Examples: tapeworms, flukes

4. Nematoda (Roundworms)

* Unsegmented, cylindrical bodies, tapered at both ends.

* Examples: pinworms, hookworms

5. Annelida (Segmented Worms)

* Segmented bodies with a distinct head and tail.

* Examples: earthworms, leeches

6. Mollusca (Mollusks)

* Soft bodies, often with a hard shell.

* Examples: snails, slugs, clams, squid, octopus

7. Arthropoda (Arthropods)

* Segmented bodies, jointed appendages, exoskeletons.

* Examples: insects, spiders, crabs, lobsters

8. Echinodermata (Echinoderms)

* Radial symmetry, spiny skin.

* Examples: starfish, sea urchins, sea cucumbers

This is just a taste of the incredible diversity of invertebrates. Remember, this is not an exhaustive list, and there are many other smaller invertebrate groups!