```html

Focus Keyword: Differences Between Vertebrates and Invertebrates

In the world of biology, vertebrates and invertebrates are two primary classifications of animals. The focus keyword "Differences Between Vertebrates and Invertebrates" refers to the distinctions between these two groups.

Main Characteristics of Vertebrates:

• Vertebrates have a backbone made of vertebrae.
• They typically have a well-developed internal skeleton.
• Most vertebrates have a distinct head with a brain enclosed in a skull.
• They possess a closed circulatory system with a heart and blood vessels.

Main Characteristics of Invertebrates:

• Invertebrates lack a backbone or vertebral column.
• They often have an exoskeleton or other support structures.
• Many invertebrates exhibit radial or bilateral symmetry.
• Some invertebrates have an open circulatory system with a heart-like structure pumping fluids.

Understanding the key differences between vertebrates and invertebrates is essential for grasping the diversity of the animal kingdom and the unique features that define each group.

```
This HTML answer provides information on the main differences between vertebrates and invertebrates while incorporating the focus keyword "Differences Between Vertebrates and Invertebrates" to enhance SEO optimization.