Tests with one central diaphragm
There are three genera of Difflugia-like amoebae which have an internal bridge or diaphragm: Pontigulasia, Lagenodifflugia and Zivkovicia. The presence of such internal construction is usually indicated by a constriction between the neck and the main body.
The simplest form is the diaphragm in the genus Lagenodifflugia. Internally the shell is partitioned into two regions by a diaphragm constructed as part of the shell wall but having a single central aperture.
Tests with a diaphragm with two or three apertures
Shells of Zivkovicia species are characterized by the presence of an internal diaphragm with two or three eccentric openings. One or more openings are sometimes sealed with organic cement embedded with small particles. Usually the diaphragm counts two openings, but sometimes specimens with a trisected diaphragm are observed. The diaphragm is always attached to the whole inner wall, visible as a belt of mineral grains.
Tests with an internal bridge
The tests of Pontigulasia species are divided internally into two parts by a small bridge, thus creating two openings. The bridge only connects two the opposite sides, without a ringlike belt of grains. Lightmicroscopically this internal bridge can be detected by the absence of a ringlike structure on the inner shell wall.
For the function of this bridge, see rotifers. At the moment the old genus Pontigulasia is split into three genera:
|1||internal diagram with one opening||Lagenodifflugia|
|–||internal diaphragm with two or three openings||2|
|2||diaphragm composed of small mineral grains, two or three circular openings||Zivkovicia|
|–||two openings formed by a small mainly organic bridge with few attached mineral particles which connects both broad sides||Pontigulasia|