Digestion is external in
(a) Echinus
(b) Ophiothrix
(c) Cucumaria
(d) Asterias

Options

A. Echinus
B. Ophiothrix
C. Cucumaria
D. Asterias.

Answer

To determine which organism exhibits external digestion among the options provided, we can analyze each option based on their digestive processes.

**Step 1: Understand the concept of external digestion.**
- External digestion is a process where an organism secretes digestive enzymes into the environment to break down food outside its body before absorbing the nutrients.

**Step 2: Evaluate each option.**
- **(a) Echinus**: This organism, commonly known as the sea urchin, has a digestive system that processes food internally. It does not exhibit external digestion.

- **(b) Ophiothrix**: Known as brittle stars, these organisms also have an internal digestive system. They do not perform external digestion.

- **(c) Cucumaria**: This is a type of sea cucumber. Like the previous two, it also digests food internally, not externally.

- **(d) Asterias**: Commonly known as the starfish, Asterias is known for its unique method of external digestion. It can extend its cardiac stomach out of its body to digest food outside before absorbing the nutrients.

**Step 3: Conclusion**
- After evaluating all options, the only organism that shows external digestion is **(d) Asterias** (starfish).

**Final Answer: (d) Asterias**

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