What are Trilobites?

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About Trilobites:

They are a group of extinct marine arthropods.
Tri-lob-ite means three-part-body in Latin.
They first appeared around 521 million years ago, shortly after the beginning of the Cambrian period, living through the majority of the Palaeozoic Era for nearly 300 million years.
They died out at the end of the Permian, 251 million years ago, killed by the end Permian mass extinction event that removed over 90% of all species on Earth.
Features:
- They are recognized by their distinctive three-lobed, three-segmented form.
- Trilobites, like other arthropods, had an external skeleton, called exoskeleton, composed of chitinous material.
- Trilobites periodically shed their exoskeleton to accommodate growth. This process is called molting. Most fossil trilobites are actually fossil trilobite molts.
- Trilobites were the first group of animals in the animal kingdom to develop complex eyes.
- They were also one of the first organisms to develop multiple appendages for moving around.
- Some trilobites could swim, others burrowed or crawled around on muddy sea floors.
- The smallest trilobite fossils are a centimeter or less in size. The largest trilobites were more than 70 cm long.

What are Arthropods?

Arthropods are invertebrates with a hard exoskeleton, a segmented body, and jointed appendages.
They make up about 75% of all animals on Earth.
Arthropods are represented in every habitat on Earth and show a great variety of adaptations.
Arthropods are divided into four major groups:
- insects;
- myriapods (including centipedes and millipedes);
- arachnids (including spiders, mites, and scorpions);
- crustaceans (including slaters, prawn, and crabs).

Q1: What are invertebrates?

Invertebrates are animals without a backbone or bony skeleton. They range in size from microscopic mites and almost invisible flies to giant squid with soccer-ball-size eyes. This is by far the largest group in the animal kingdom: 97 percent of all animals are invertebrates.

Source: Trilobite fossils from upstate New York reveal extra set of legs