I imported the front and left side views of the design into Maya and added them to an unselectable layer so that I can model with guides that won’t be selected whilst modelling.
Ideally, a cylindrical shape would’ve been best to start with but I figured the faces on the bottom would be awkward to use for the tentacles, so I started with a cube. I selected all of the vertices on each corner and moved them to the furthest points on the references to map out how big I would need the cylinder to be. I then made a sphere the same size as the four points and placed it above the cube and then started moving all of the vertices on the cube to match the circumference of the sphere. That gave me a cylindrical shape with the end faces of a cube. After that I just selected groups of edges and expanded or contracted to get the width of the cylinder in different areas roughly correct. I also used the soft selection tool to raise the top faces evenly.
In hindsight, I probably could’ve made a cylinder and cube and deleted the faces I didn’t want and connected the rest together.
Below, in white, are the attempts before the one shown above, not including the model that disappeared on me.
The left most white model I got the tentacles out front and back, but I couldn’t get them to look natural going diagonally. probably because of how flat/square the whole thing was. The next one I was having difficulty just doing the tentacles at all. I then tried a different way of doing them on the third model but that only worked if you’re looking at it straight on. The fourth model I moved vertices using symmetry but that didn’t quite give the natural spherical look, and the bottom was still very square.