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.
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”.