The Egenoid Star Marines are a group mentioned in a Pirate Data entry in Metroid Prime in the Phazon Mines. The Star Marines seem to be the original owners of all Plasma Artillery Cannons seen in-game, as the log entry states that the Space Pirates 'acquired' (stole) the cannons from their warehouse in order to have them mounted on the shoulders of Elite Pirates. The marines have not been mentioned since.
It is unknown if they have any connection to the Galactic Federation Marine Corps.
"A shipment of military-grade Plasma Artillery Cannons is en route to Tallon IV. The Egenoid Star Marines we 'acquired' them from were letting them sit in a warehouse. Our Elite Pirates, on the other hand, will put them to good use very soon."