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Clathrulina elegans
Clathrulina elegans. a morphology; b one specimen with long stalk and two specimens on top of each other; c test with two cysts; d ovoid test; e nucleus; f cross section of two edges of the openings (from Siemensma, 1991)

Clathrulina elegans Cienkowski, 1867

Diagnosis: shell spherical, stalked, more or less chitinous, colorless to brown, perforated by numerous comparatively large circular or polygonal openings, usually regularly placed; stalk long and hollow, with some root–like structures at its base; protoplasm not filling the test; nucleus single, placed centrally; one or more contractile vacuoles; pseudopodia very delicate, without axial filaments; solitary or colonial; cell divides and produces flagellated dispersal stages.

Dimensions: Literature: diameter 30-92 µm; openings 6-10 µm; length of stalk usually two to four times the diameter of the shell, up to 260 µm, 1-4 µm wide. My measurements: 32-97 µm; stalk up to 280 µm long, more than eight (!) times the diameter of the shell.

Ecology: Sphagnum swamps and among aquatic plants in ponds; locally common.

Remarks: It might be possible that there are more than one species. Deflandre (1926) described Clathrulina ovalis, but this species is considered to be a synonym of C. elegans. Young et al. (1995) discovered during the course of a detailed investigation of the plankton dynamics of Loch Ness, Scotland, a stalkless form of Clathrulina living in the plankton. This heliozoon was established in culture and its life-cycle events observed. Though broadly similar to the sequence of events described by Bardele (1972) for Clathrulina elegans, it differs in respect of lacking a stalk and in the number of fission products produced. Young et al. propose the name Clathrulina elegans var. planktonicum for this planktonic form of the species living in the pelagic zone of Loch Ness.

Reference: Young, J., Laybourn-Parry, J., Jones, R.I. and Walton, M. (1995): A stalkless sub-species of Clathrulina elegans Cienkowski (1867) from the plankton of Loch Ness, Scotland. Eur. J. of Protist., 31, 1, 15; pp. 54-57.

Clathrulina elegans
Clathrulina elegans
C elegans, 63 µm, Haaksbergerveen, stacked and shell 38 µm, stacked image, Den Treek
Clathrulina elegans
Stacked image – the Netherlands, 2019
Clathrulina elegans
Capturing prey
Clathrulina elegans
Clathrulina elegans
C. elegans, nucleus with at least three nucleoli (l.) and shell, stacked image (r.)
Clathrulina elegans
Clathrulina elegans
Cysts
Clathrulina elegans
Clathrulina elegans
End of stalk; empty shell, 52 µm – Austria
Clathrulina elegans
Clathrulina elegans
Shell 40 µm
Clathrulina elegans
C. elegans, shell 35 µm, stalk 112 µm.
Clathrulina elegans
C. elegans, shell 33 µm, stalk 280 µm.
Clathrulina elegans
C. elegans, shell 34 µm, stalk 268 µm.
Clathrulina elegans
Clathrulina elegans
C. elegans, Austria, and cyst
Clathrulina elegans
Clathrulina elegans
C. elegans, both from Sphagnum, moor near Haaksbergen, the Netherlands (2018)
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