In echinoderms, the digestive system is

Options

A. complete
B. incomplete
C. absent
D. Either (B) or (C)

Answer

**Step-by-Step Text Solution:**

1. **Understanding Echinoderms**: Echinoderms are a group of marine invertebrates that include starfish, sea urchins, and sea cucumbers. They belong to the phylum Echinodermata.

2. **Identifying the Type of Digestive System**: The question asks about the type of digestive system present in echinoderms.

3. **Complete Digestive System**: Echinoderms possess a complete digestive system. This means they have a digestive tract that runs from the mouth to the anus.

4. **Tube-Within-Tube Body Plan**: The complete digestive system in echinoderms is described as a "tube-within-a-tube" body plan. This indicates that there are two separate openings: one for ingestion (the mouth) and one for excretion (the anus).

5. **Conclusion**: Therefore, the digestive system in echinoderms is a complete digestive system characterized by the presence of both a mouth and an anus.

**Final Answer**: The digestive system in echinoderms is a complete digestive system.

---