Arcella costata var angulosa? (Perty) Playfair

Specimen #25356-358:

Diameter shell: 110.3 µm

Diameter aperture: 32.3 µm

Height shell: 68.4 µm

Bucal depth: 24.1 µm

Arcella costata Ehrenberg

Specimen #25602-604 (left):

Diameter shell: 108.0 µm

Diameter aperture: 37.4 µm

Height shell: 57.0 µm

Specimen #25602-604 (right):

Diameter shell: 105.8 µm

Diameter aperture: 38.1 µm

Arcella sp2

Specimen # 22187:
Diameter shell: 91.4 µm

Specimen # 21892:
Diameter shell: 95.5 µm

Diameter aperture: 24.5 µm

Specimen # 20577:

Diameter shell: 112.9 µm

Specimen # 20598:
Diameter shell: 104.1 µm

I could not measure the diameter of the aperture for some of the specimens. Unfortunately, all these specimens were only photographed on one side (apical view). For now on I will try to photograph all the necessary diagnostic taxonomic characters and all the possible views.

I think all these specimens are similar to Arcella costata. I posted Specimen #20577 earlier. It appears in a picture next to another specimen that I called Arcella megastoma.

Arcella costata? Ehrenberg

Specimen #25054:
Diameter shell: 101.1 µm

Specimen #22491:
Diameter shell: 108.8 µm
Diameter aperture: 30.5 µm

Specimen #21041:
Diameter shell: 97.6 µm
Diameter aperture: 29.9 µm

Specimen #10864:
Diameter shell: 121.8 µm
Diameter aperture: 34.6 µm

Arcella megastoma Pénard & Arcella costata? Ehrenberg

Arcella megastoma (right)
Diameter aperture: 351.2 µm
Diameter shell: 171.1 µm

Arcella costata? (left)
Diameter aperture: 112.9 µm