Bilateria

Bilateria are a big group of animals that have a special way of building their bodies. Most animals you know, like insects, fish, birds, and even humans, belong to this group. They share something called bilateral symmetry. This means they have a head and a tail end, and their left and right sides look almost the same.

All bilaterians start life with this body plan, even if they look different when they grow up. This helps them move in one direction and find food easily. Many have a mouth and an anus, with a simple gut connecting them. Some even have nerves that help them sense the world around them.

Scientists believe the first bilaterian looked like a tiny sea worm. These amazing animals have been around for more than 555 million years! They are very important because most animals on Earth today are bilaterians. They are split into two big families: deuterostomes and protostomes, which differ in how their babies grow inside.