Diaphragm

Testate amoebae 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 orifice.

Lagenodifflugia vas
Lagenodifflugia vas
Shell of a Lagenodifflugia spec. A dark band between neck and body indicates the presence of the internal diaphragm. The arrow points to the orifice in the internal diaphragm as visible through the shell wall.

Testate amoebae with a diaphragm with two or three eccentric openings

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.

Lagenodifflugia vas
Lagenodifflugia vas
Shell with an internal diaphragm with one eccentric opening (arrow). The same shell, but now in apertural view, showing one opening, but it looks as if there is a second closed opening (beneath) and maybe a third one to the left.

Zivkovicia spec

A specimen with three openings in the diaphragm.

Testate amoebae with a small 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.

Pontigulasia bridge
Pontigulasia bridge
Shell with an internal diaphragm with two openings. The black arrow points to the bridge, the white arrows point to both openings. (r) The same shell, but now in apertural view, looking into the pseudostome where the bridge is clearly visible.

For the function of this bridge, see rotifers.   At the moment the old genus Pontigulasia is split into three genera:

1internal diagram with one openingLagenodifflugia
internal diaphragm with two or three openings2
2diaphragm composed of small mineral grains, two or three circular openingsZivkovicia
two openings formed by a small mainly organic bridge with few attached mineral particles which connects both broad sidesPontigulasia
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