Reprint of TALES TO ASTONISH #1 (1959), inks attributed to Chris Rule.
A ship encounters a giant lobster, just one in a series of giant sea life they've encountered as Professor Briggs leads them on an expedition following the map of Doctor Parker. The ship is capsized by what seems to be a giant moving island, and Briggs and Captain Kane wind up on the shore of another island, where they find Parker. Turns out he'd been conducting experiments on hormone regulating systems, but hadn't yet found a way to control it, leading to the giant turtle currently escaping from behind a huge gate. As they flee, Kane considers the potential wealth and problems of taking such a giant beast to civilization.
Ultimately he decides not to, and on the way out they encounter an even bigger turtle from an earlier experiment, the very "island" that had capsized the ship.
A hodge-podge of ideas already cliche as the time, borrowing heavily from KING KONG of course. The monsters in this are also a let-down, being just large versions of real animals. I did like the odd perspective shot of the stockades that the turtle was held in, though.
The cover is also from TALES TO ASTONISH #1, also Kirby/Rule, but heavily modified for the reprint. In the original the monster shown through the gates is clearly a large turtle, just walking out, as in the story, in the reprint it's completely redrawn as some huge snarling clawed beast.