Happy printing, and if you like my models you can follow me for more awesomeness!

I designed this sea-mine last month as a challenge for our pet crayfish Crusty. He was always climbing everything (air pipes, thermometer, plants) and is extremely driven by food. 

Searching the internet I found similar designs with the concept I was looking for but none that could print support-free and had a good solution to keep the base at the bottom while the mine has good floatation.

That's why I designed my own. It consists of two halves that can fit a standard table tennis ball in order to float well. There are three separate pins that twist-lock the halves together, requiring no glue or fasteners. The print-in-place chain also gets sandwiched between the halves completing the mine.

Because it encapsulates a table tennis ball there is a lot of floatation, allowing even heavier crustaceans to climb to the top. The base is extra large but a couple of stones are already enough to anchor it to the bottom.

There are also four holes where an optional screw can be inserted from the inside out to which food can be attached. 

It took some training to get Crusty on the mine the first time (we stuck some corn inside the chain) but once he has been up there, every time he walks by and sees some color he'll climb right up to check it out!

Edit:

After user feedback I've added 4 extra pins, 2 undersized and 2 oversized. The pins twist-lock the two halves together and should snap in place. I used pliers for mine to twist them to ensure a good ‘lock’ with the tightest tolerance I could get away with (standard size). If you can't twist the pins you should downsize and if they twist (almost) freely try one or two sizes up. Glue shouldn't be necessary and most glues are not advised for aquatic use.