Triploblastic animals possess an extra layer called________.

Explanation

**Step-by-Step Solution:**

1. **Understanding Triploblastic Animals**: Triploblastic animals are organisms that have three primary germ layers during their embryonic development. These layers are critical for the formation of various tissues and organs in the body.

2. **Identifying the Germ Layers**: The three germ layers in triploblastic animals are:
- **Ectoderm**: The outermost layer, which develops into the skin and nervous system.
- **Mesoderm**: The middle layer, which forms muscles, the circulatory system, and other internal structures.
- **Endoderm**: The innermost layer, which develops into the digestive tract and associated organs.
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