This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Gegenees (Greek)
The Gegenees were a race of six-armed giants who inhabited the same island as the Doliones in the ancient Greek epic Argonautica. They were also called Gegeines. Jason and the Argonauts landed on an island where the Gegenees resided. The Argonauts fought them and unknowingly left Heracles on the island where he continued to fight them. The Argonauts returned and were able to help Heracles fight them off.
The Gegenees were named as children of Gaia; as indeed were many of the giants of Greek mythology, including the Gigantes. The Gegenees were of prodigious size, but their distinguishing feature was the fact that they had six arms, two protruding from their shoulders, and a further two pairs from their rib cage.