It's incredible enough that these protozoans can build houses but that they can design each 'door opening' so that it interlocks with another's 'door opening' is mind boggling.
The following description from
HERE
"The animal generally creeps about head-downwards,so to speak;
that is to say, with the closed end of the carapace elevated
above the surface on which it is moving. Difflugioe often exhibit
the phenomenon known as "conjugation" or "zygosis." Under these
circumstances, two Difflugioe come in contact; the mouths of the
two tests are brought together ; the two animals flow backwards
and forwards into each other's tests, with an apparently complete
incorporation; and finally they separate again, and each retires to its own test."
BHS 10x S Plan Apo 1.25x intermediate lens 2.5x relay lens
11 frames, ZS PMax

NU11001