The Gigas Worm is a Soul of Rebirth enemy in Final Fantasy II. It is found in Raqia and, though a tribute in the new versions, are a lot harder than their Final Fantasy namesakes. Until the party gets at least Josef in the party, these enemies are rather dangerous and can easily fell both Minwu and Scott with no problem. With both Josef and Ricard, the enemies become less of a threat. If the party has any decently leveled Fire spells, they can use them to defeat the worms quickly.
Gigas is a popular term for races of giants in fantasy games. Gigas is a Greek word meaning "giant," originally used to describe the race of Gigantes in Greek mythology and is used in the scientific name, as the specific epithet, of hundreds of species of animals and dozens of plant species to denote their size.