What is retrogressive metamorphosis?

Explanation

**Step-by-Step Solution:**

1. **Definition of Retrogressive Metamorphosis**: Retrogressive metamorphosis refers to a type of metamorphosis characterized by degenerative changes in an organism. In this process, the active larval form transforms into a more sedentary adult form.

2. **Characteristics of the Process**: During retrogressive metamorphosis, the larva, which is usually mobile and active, undergoes significant changes that lead to a reduction in its structures. This includes the loss or simplification of certain features that were present in the larval stage.

3. **Example of Organisms**: A notable example of retrogressive metamorphosis can be found in urochordates, such as the genus Herdmania. In these organisms, the notochord, which is a flexible rod-like structure, is present only in the larval stage, specifically in the tail.

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