Which phylum includes exclusively marine non-parasitic forms of animals ?

Options

A. Porifera
B. Cnidaria
C. Molluscs
D. Echinoderms

Answer

To solve the question "Which phylum includes exclusively marine non-parasitic forms of animals?" we will analyze each of the provided options step by step.

### Step 1: Analyze Phylum Porifera
- Porifera, commonly known as sponges, are primarily aquatic animals.
- They can be found in both marine and freshwater environments.
- Therefore, Porifera does not exclusively consist of marine forms.

**Hint:** Consider the habitat of organisms in this phylum and whether they are found in both marine and freshwater.

### Step 2: Analyze Phylum Cnidaria
- Cnidaria includes jellyfish, corals, and sea anemones.
- Most members of this phylum are aquatic and can be found in both marine and freshwater environments.
- Thus, Cnidaria also does not exclusively include marine forms.

**Hint:** Think about the diversity of habitats for organisms in this phylum.

### Step 3: Analyze Phylum Mollusca
- Mollusca includes a wide range of animals such as snails, clams, and octopuses.
- Members of this phylum can be found in terrestrial, freshwater, and marine environments.
- Therefore, Mollusca is not exclusively marine.

**Hint:** Reflect on the various environments where mollusks can thrive.

### Step 4: Analyze Phylum Echinodermata
- Echinodermata includes starfish, sea urchins, and sea cucumbers.
- All members of this phylum are exclusively marine and are typically found on the ocean floor.
- They do not include any freshwater or terrestrial species.

**Hint:** Focus on the specific habitat of echinoderms and their exclusivity to marine environments.

### Conclusion
After analyzing all the options, the phylum that includes exclusively marine non-parasitic forms of animals is **D. Echinodermata**.

**Final Answer:** D. Echinodermata