Excretory organs are absent in
(a) Asterias
(b) Sepia
(c) Unio
(d) Pila

Options

A. Asterias
B. Sepia
C. Unio
D. Pila.

Answer

To determine which organism among the given options lacks excretory organs, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which of the listed organisms does not have excretory organs.

2. **Analyzing Option (a) Asterias**:
- Asterias is a genus of starfish belonging to the phylum Echinodermata.
- It is known that echinoderms, including Asterias, do not have specialized excretory organs. Instead, they excrete waste products through diffusion across their body surfaces.
- Therefore, Asterias does not possess any excretory organs.

3. **Analyzing Option (b) Sepia**:
- Sepia, commonly known as cuttlefish, belongs to the class Cephalopoda.
- It has excretory organs known as renal sacs, which are responsible for the removal of waste.
- Thus, Sepia does have excretory organs.

4. **Analyzing Option (c) Unio**:
- Unio is a genus of freshwater mussels, belonging to the class Bivalvia.
- It possesses excretory organs known as the organs of Bojanus, which function similarly to kidneys.
- Therefore, Unio does have excretory organs.

5. **Analyzing Option (d) Pila**:
- Pila is a genus of freshwater snails, belonging to the class Gastropoda.
- It has a kidney that consists of two renal chambers, which serve as its excretory organ.
- Hence, Pila does have excretory organs.

6. **Conclusion**: After analyzing all the options, it is clear that the only organism that lacks excretory organs is **Asterias**.

### Final Answer:
**(a) Asterias**

---