Possible Clues:

• *'The Mystic'
• Writer turned up with simple air — Holst wrote it
• Sea god put erroneously in river
• God! It's next to Uranus
• Remote planet
• Poseidon, to Romans
• Name old record with melody that's in Holst's suite
• Planet - sea god
• Roman god of water and the sea
• Record plugging new melody, part of The Planets