👉 Mesometridae are a group of marine invertebrates, including the common sea urchin (Ustilago grisea) and the red sea urchin (Ustilago stenophila). These animals have complex structures made up of several groups: the head, thorax, abdomen, and pelvic fin. They are known for their ability to regenerate lost limbs, a trait that is crucial in marine ecosystems as it allows them to adapt to changing conditions over time
