What are Trilobites?

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