Rhizaspis armata – Microworld

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.

R. armata, 51 µm – Den Treek, Netherlands

R. armata, 68 µm long, excl. spines; some filopodia are visible to the left; note the large granules.

R. armata, apertural view; the cell hangs on the cover glass.

R. armata, from the Naardermeer, 57 µm

R. armata, with detail showing that spines are modifications of the membrane

R. armata, mouth (arrow) – both specimens from Den Treek, Amersfoort

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)

R. armata, filopodia – Phase Contrast

R. armata, filopodia – DIC

The original description with original drawings, Penard, 1890.

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).

Drawing in Cash, Wailes and Hopkinson (1915)

R. armata – Photo: Eckhard Voelcker, Berlin, and R. spinosum, apical view

R. spinosum – Photomicrograph: Eckhard Voelcker, Berlin

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”.