Terrapin or some mad creature to suit a 'small' fully aquatic tank??

[tickle]

Hi, i am currently planning what to fill my 200 litre tank with and could do with a pointer or two.

I will be buying a pair of Pearl Crayfish, a trio of Vampire Shrimp, and an array of Glass / Crystal Red Shrimp.

What i am unsure of is what else to have, i would really like to have a terrapin or two and would happily sacrafice the shrimp to do so, however, i am not willing to lower the water volume to trade off for a turtle dock.

Is there a fully aquatic species small enough to get in there?

If not i am likely going to go with some wild caught Betta Imbellis or something more peculiar if anyone has any suggestions?

The perameters i am 'loosly' aiming for are 22-26 Celcius, PH nuetral (maybe mildly alkaline), and will be adding a small amount of argonite to raise calcium levels for the crays. The temperature being the only truly flexible point as i want to avoid pitting on the crays carpace.

 

[tickle]

*tumbleweed* *more tumbleweed*

The tumbleweed and google tells me the terrapins are not going to happen without a land area and bask light,

however, anyone able to shed some light on a peculiar fish that could join the ranks?
All worrying about crayfish compatibilty aside, just something that 'loosly' matches the peramiters above,

I have spent weeks looking through photo's and index's and nothing, the closest things i found are Betta's, or blue cobalt / jack dempsey cichlids. Nothing that really demands to be stared at for any large amount of time imo.