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Rhizaspis scutiformis, filopodiaLaegieskamp

Genus Rhizaspis Skuja 1948 emend. Dumack et al, 2017
= Plagiophrys Claparède & Lachmann, 1859

Diagnosis: Thecate amoebae with ventral slit-like, but flexible, cleft that emits filopodia; theca thin, flexible, in active cells adherent throughout to cell surface, with exosomes (R. parvipunctata) or without (all other species), sometimes deformed by ingested food, often wrinkled or folded, consisting of single smooth dense layer outside and scarcely thicker than the plasma membrane; thus with bilateral symmetry (ventral flattened). Round nucleus; nucleoli may be visible by light microscopy, often one, sometimes several. Cells may be divided in zones (basal to apical): several contractile vacuoles, food vacuoles, nucleus embedded by a large number of in size varying granules. Inhabiting fresh-waters. Eukaryvorous, mainly feeding on algae, especially diatoms. Division longitudinal, binary. Sexual reproduction unknown.

Type species: R. granulata Skuja 1948

Species:

Most species are hardly distinguishable by light microscopy. A main character might be the presence of one central nucleolus versus several nucleoli.

 

1Test with a median rib terminating into a sharp pointR. arcuatus
Test without median rib2
2Nucleus with central nucleolusR. granulata
R. simplex
Nucleus without central nucleolus3
3Test without rib or wings4
Shell with distinct keel or wings5
4R. transformis
R. rugosa
5Edge usually smoothR. scutiformis
Edge with many wrinkelsR. marginata

 

Plagiophrys scutiformis
R. scutiformis, 60 µm – Tirol, Austria
cf R. transformis, 58 µm, Florida USA; (R) Small spines on the keel – bar = 10 µm
Both from the Netherlands
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