Nautilus transforming

Maleko’s jaw trembled. He took in three more short breaths. The muscles in his arms and neck tensed. He inhaled three more times, his face darkened as if he was holding his breath for too long, and he closed his eyes.
St. George realized the man hadn’t let any air out yet.
Veins bulged on Maleko’s arms and chest and neck and face, like a bodybuilder at the peak of his workout.
…
Dark bruises burst across Maleko’s skin. The flesh under his eyebrows puffed up. Hives broke out across his bare shoulders, flowed together, and bubbled up even more.
He opened his eyes. They were all black. Black and oily. He bared jagged teeth in a snarl.
…
Maleko grew.
He threw his head back, and by the time his ponytail settled he was a foot taller. His chest swelled inside the baggy clothes until the silk shirt was tight at the seams. The cord he’d been using as a belt snapped, and then the ragged slacks were tight, too. His arms and neck thickened under the bulging veins.
His hands spread wide. The palms widened, and the fingers shrank to little stubs with one knuckle. Then the hands flexed again, and St. George realized the palm hadn’t grown at all.
The fingers were webbed.
He glanced down and saw Maleko’s toes had stretched out. Just enough that the webbing there was apparent. The toenails curled into short claws.
The growths on his shoulders rippled and continued to swell. The bruised skin paled, but to a glossy blue-gray, not the golden brown it had been. His shoulders lost even more color and hardened until they were like bone.
Or shell.
“Whoa,” said Madelyn. “Nautilus.”
Maleko twisted his head in a slow circle until his neck popped. His black eyes gazed down at St. George, shaded by a Neanderthal brow.

Excerpt From Ex-Isle, pg 328-330
Peter Clines
https://books.apple.com/us/book/ex-isle/id989619017