As the name suggests invertebrates have no spines, and modern examples of them include worms, slugs, and even flies! 
   They appeared at the beginning of the of the Cambrian (way back in the Paleozoic over 540 million years ago!), and included clams, gastropods, Sea urchins, and more.

Fossil Trilobite

• 540-252 million years old.
• Trilobites lived long before the dinosaurs!

Fossil Belemite

• Found in NJ
• 144-66 million years old (Cretaceous).
• Also known as a Squid Pen, as it is the fossilized skeleton of a squid.

Fossil Orthoceras

• 500-200 million years old.
• A type of extinct cephalopod, the same family as modern squids.

Fossil Ammonites

• Found in Madagascar.
• 240-65 million years old.
• Ammonites were like little coiled squids that used jet propulsion to get around the water.

Fossil Clams

• Clams has been around for over 500 million years!

Sea Urchin 

• Found in Madagascar.
• Sea Urchins are over 500 million years old!

Gastropod

• Around 15,000 fossils species have been identified.
• Slugs are gastropods, they just don't have shells.

Brachiopod