Its center section-the core-glows brightly in seven colors. Because of its luminous nature, this Pokémon has been given the nickname "the gem of the sea."
(From Bulbapedia) Starmie is a violet sea star-like Pokémon with a gold formation on its front. Starmie's jewel core, which can glow in seven colors, has developed to resemble a cut precious stone. There is second set of semi-attached arms on its back, which are able to spin 360°. Starmie can emit electrical waves from the core that are powerful enough to reach the furthest parts of the universe.
The multi-color glowing of its core is also believed to be a method of communication inside the species. However, Starmie’s core is most commonly seen as red in color. Because of its body shape and habit of sending transmissions skyward, some people believe this Pokémon to be extraterrestrial. Starmie is rarely seen in the wild, but can be found in the deepest parts of the ocean. It is Lumineon's favourite food.
(From Bulbapedia) Starmie appears to be a stylized starfish. Given its ties to outer space, it may also be a pun on a literal star.
Starmie's gem being cut evokes the idea of some form of jewelry. Notably, the eight facets prominently witnessed upon Starmie's gemstone (adjacent to the center facet) would be called the star facets, were it a real jewel.
Starmie also bears some resemblance to the Star of Ishtar. Ishtar, also called Inanna, is known as Queen of Heaven.
(From Bulbapedia) Starmie may be derived from star (referring to its shape) and mie, which may involve 珠 mi (gem or jewel), referring to its core. In English, mie may be a corruption of me (the personal pronoun), in contrast to the yu (you) in Staryu.