LEGO 5451 Musical Sea Mobile was a Explore set released in 2003. It is possible the set was never actually released.
There are currently no new/sealed listings available for Musical Sea Mobile at this time.
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Sets in Explore / Being Me

5449 Stack 'n' Learn Sorter

Theme / Subtheme Explore / Being Me
Year 2003
Pieces 13
Availability Retired
5449 LEGO Being Me Stack 'n' Learn Sorter
Retail $6.99
Value $27.04
Growth  +286.8%
Annual growth 5.9%

5441 Smiling Rattle

Theme / Subtheme Explore / Being Me
Year 2003
Pieces 2
Availability Retired
5441 LEGO Being Me Smiling Rattle
Retail $4.49
Value $34.18
Growth  +661.2%
Annual growth 9.7%

5443 Curly Hanging Rattle

Theme / Subtheme Explore / Being Me
Year 2003
Pieces 2
Availability Retired
5443 LEGO Being Me Curly Hanging Rattle
Retail $5.99
Value $30.26
Growth  +405.2%
Annual growth 7.6%

5450 Discovery Bird

Theme / Subtheme Explore / Being Me
Year 2003
Pieces 2
Availability Retired
5450 LEGO Being Me Discovery Bird
Retail $12.99
Value $44.50
Growth  +242.6%
Annual growth 5.8%

5446 Roll 'n' Tip

Theme / Subtheme Explore / Being Me
Year 2003
Pieces 1
Availability Retired
5446 LEGO Being Me Roll 'n' Tip
Retail $9.99
Value $39.94
Growth  +299.8%
Annual growth 6.5%