Step 1: Recall which bodies have explicit constitutional status.
- UPSC is established under Article 315.
- Election Commission of India (ECI) is under Article 324.
- Finance Commission is constituted under Article 280.
Step 2: Check NITI Aayog’s status. NITI Aayog (established in 2015 by executive resolution) replaced the Planning Commission. It is a {non-constitutional, non-statutory} body.
Step 3: Conclude.
\[
\boxed{\text{NITI Aayog (Option D) is not a constitutional body.}}
\]