WORMs

The Weapon of Raid Machines, or WORMs, are artificial lifeforms consisting of millions of nanocells. They're the main antagonists of the series. The WORMs are able to take forms of life they see. These machines were responsible for annihilating one third of earth's population. Although most are defeated in the war, some survived and resurfaced. The remaining WORMs are combated by the Sky Girls and their Sonic Divers.

OVA
The one that appeared in the original video animation resembled a monstorous starfish with multiple arms and has green eyes on the front.

Episode 9
The first real WORM the Sky Girls faced ressembled a giant turtle. The shell is purple and the skin is red. On its back has a bunch of projectile shells which it launches at its enemies. This WORM was found in sea near an oil refinery.