A phylum in which the digestion is intracellular as well as extracellular and polyp body form is seen includes organisms which:

Options

A. Are triploblastic.
B. Show internal fertilization and indirect development.
C. Have special cells called choanocytes.
D. Have a central gastro-vascular cavity with a single opening.

Answer

To solve the question regarding the phylum that exhibits both intracellular and extracellular digestion and has a polyp body form, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Key Characteristics**:
- The question states that the phylum has both intracellular and extracellular digestion.
- It also mentions the presence of a polyp body form.

2. **Determine the Relevant Phylum**:
- The phylum that fits these characteristics is **Cnidaria** (previously referred to as Coelenterata).
- Cnidarians exhibit two body forms: the polyp (sessile) and the medusa (free-swimming).

3. **Understanding Digestion**:
- In Cnidarians, digestion occurs in two ways:
- **Intracellular Digestion**: Food particles are engulfed by cells and digested within them.
- **Extracellular Digestion**: Digestion occurs in the gastrovascular cavity where enzymes break down food before it is absorbed by the cells lining the cavity.

4. **Analyze the Options**:
- **Option A**: "Diploblastic" - This is true for Cnidarians as they have two germ layers (ectoderm and endoderm).
- **Option B**: "Shows internal fertilization and indirect development" - This is incorrect for Cnidarians; they typically exhibit external fertilization.
- **Option C**: "Have special cells called choanocytes" - This is incorrect as choanocytes are characteristic of Porifera (sponges).
- **Option D**: "Have a central gastrovascular cavity with a single opening" - This is correct for Cnidarians, as they possess a gastrovascular cavity that serves as both a mouth and an anus.

5. **Conclusion**:
- Based on the analysis, the correct answer is **Option D**: "Have a central gastrovascular cavity with a single opening".