Pyxidicula husvikensis

 

From Beyens & Chardez, 1997

Microcorycia husvikensis Beyens & Chardez, 1997

 

See Pyxidicula husvikensis

 

Diagnosis: It mainly follows the subsequent description by Chardez (1999), which is more precise and detailed than the original description:
The upper test part is dome-shaped and has a yellowish tinting. A very delicate punctuation is visible at high magnification. The margin of the upper test part is divided into an external part and an internal part. The internal margin changes into a flexible, hyaline membrane, which spreads towards the periphery and forms a border around the upper test part. This membrane can fold up towards the centre as to reduce the diameter of pseudostoma. The upper test part of young individuals is hyaline and more pliable than with older ones.
The cell body is located as a spherical or oval mass in the test and is connected to the upper test part through fine ectoplasmatic epipodia of varying number (two or three). Pseudopodia are lobate. Cytoplasm is finely granulate. It contains numerous inclusions (excreta and glycogen granules) and a contractile vacuole. The cell is mononuclear. The nucleus contains a central nucleolus. The nucleus has a diameter of 2.4-3,0 µm.

Encystment: Two types of cysts have been found. The resting cyst is formed inside the test. It is completely spherical in shape and has a diameter of 24 µm. Cytoplasm is dense and opaque. It is surrounded by a smooth membrane. Moreover, the cell can change into the state of pre-encystment. In pre-encysted state, the membrane is rough and irregular; it is attached to a test point. Pre-encysted cytoplasm has a diameter of about 28 pm . The lower test part is folded towards the peristome centre. The margin of the upper test part can also be folded inwards for reducing the test opening.

Dimensions: diameter upper test part 32-35 µm, height 16-20 µm, diameter including the spread lower test part: 39-43 µm.

Ecology : Slightly alkaline lakes and ponds, vegetated by moss (Beyens &  Chardez 1997), moss (Chardez 1999). So far only known from the subantarctic island of South Georgia.

Remarks: What is striking with M. husvikensis is that the lower test part has only a small height compared with other Microcorycia species. Thus it is assumed that the pseudostoma cannot be completely closed. Obviously M. husvikensis is a primordial form of Microcorycia.

All from Badewitz, 2004
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