For full Megachelon taming details, get the taming calculator app.
The Megachelon is a passive tame. To tame it, find a small swarm of fish, and lure them over to.a Megachelon. Swim along side the turtle with the swarm to tame it. You may be able to get close enough to feed it food, but this is confirmed to be a bug and not intended. Please share your strategies in the Tips section!
Tamed you'll be able to build on its back. When diving he provides an oxygen bubble on his back allowing you to submerge your base on the floor of the ocean.
Are you turtley enough for the turtle club?