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Rhizaspis armata
R. armata, 68 µm long, excl. spines – Laegieskamp

Rhizaspis armata (Lauterborn, 1901) Dumack et al., 2021
Basionym: Pamphagus armatum Lauterborn, 1890

Diagnosis: Theca membranous, ovoid or pyriform, in dorsal view circular or a little compressed, with numerous curved spines, which are modifications of the membrane; aperture sub-terminal, oblique and pliable; nucleus granular, placed posteriorly; cytoplasm filling the test; filopodia numerous, simple or branched, sometimes anastomosing.

Ecology: Freshwater, aquatic vegetation (Hopkinson, 1915), sediments (Lauterborn, 1901). I have found one specimen in the sediments of a forest pond at Groeneveld, Baarn, the Netherlands, in 1981. I found some specimens again in the ooze of ditches in Den Treek (2012), Laegieskamp (2013) and Naardermeer (2015).

Dimensions: Length 53.5 ± 3.6 µm, width 36.7 ± 11.2 µm.

Remarks: This species has been described by Penard (1890) as Trinema spinosum, but his species is much smaller, though Penard (1902) accepted the name Pamphagus armatus.

Reference: Dumack, K., Siemensma, F., Clauß, S. 2021. Transfer of the thecate amoebae Lecythium spinosum and Pamphagus armatus to Rhizaspis (Thecofilosea, Cercozoa, Rhizaria), European Journal of Protistology, 125843, ISSN 0932-4739, https://doi.org/10.1016/j.ejop.2021.125843.

Lecythium spinosum with filopodia
R. armata, 51 µm – Den Treek, Netherlands
Rhizaspis armata
R. armata, 68 µm long, excl. spines; some filopodia are visible to the left; note the large granules.
Rhizaspis armata
R. armata, apertural view; the cell hangs on the cover glass.
R. armata, from the Naardermeer, 57 µm
Rhizaspis armata
Rhizaspis armata
R. armata, with detail showing that spines are modifications of the membrane
Lecythium spinosum
Lecythium spinosum
R. armata, mouth (arrow) – both specimens from Den Treek, Amersfoort
Rhizaspis armata
R. armata with large food vacuole, body 58 µm long; in the fundus region the nucleus is visible, but without distinct visible structure. It looks if the nucleolar material is fragmented and sausage shaped – Den Treek, Amersfoort
Specimen from the Naardermeer (70 µm)
Specimen from the Naardermeer (75 µm)
Rhizaspis armata
R. armata, filopodia – Phase Contrast
Rhizaspis armata
R. armata, filopodia – DIC
The original description with original drawings, Penard, 1890.
Pamphagus armatus
Rhizaspis armata
Left: Drawing of R. spinosum by Penard (1902). He considered this specimen as a Trinema-species (Penard, 1890), but corrected his identification later in Pamphagus armatus, giving the credit to Lauterborn.
Right: Drawing of Pamphagus armatus by Lauterborn (1901).
Rhizaspis armata
Drawing in Cash, Wailes and Hopkinson (1915)
Rhizaspis armata
Rhizaspis armata
R. armata – Photo: Eckhard Voelcker, Berlin, and R. spinosum, apical view
Rhizaspis armata
R. spinosum – Photomicrograph: Eckhard Voelcker, Berlin
Lecythium spinosum
R. armata (Length 49 µm, width 37 µm) – drawing Ferry Siemensma

The photomicrographs below were made by Francisco Pujante, Spain, and might represent R. spinosum or a closely related species:

According to Francisco, his sample comes from Parque La Albufera in Valencia in Spain, freshwater with moderate pollution. Water temperature approx. 18 º Celsius. The lake is fed by the river Turia and is in contact with the Mediterranean Sea through various channels. All around the lake are rice fields flooded with water for several months a year. He “found a lot of them”.

Rhizaspis armata
R. armata –, still from Youtube, published by Francisco Pujante Capilla, Febr. 15, 2017.
Rhizaspis armata
Rhizaspis armata
Rhizaspis armata
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