Arcella excavata
Arcella excavata, Ø c. 44 µm - the Netherlands

 

 

Arcella excavata Cunningham, 1919

 

Diagnosis: shell colorless or yellowish in young specimens and brown in older cells, oval or circular in apertural view and croissant-like in lateral view; large axis of the shell (length) usually in perpendicular direction to the shell’s protuberances, when the shape of the shell in apertural view is not circular; sometimes the large axis of the shell is parallel to the shell’s protuberances; apertural surface deeply invaginated forming two pronounced protuberances with circular or elliptical aperture at the bottom of invagination; aperture bordered by a small lip; aboral hemispherical region smooth or with regular depressions; shell wall composed of numerous alveoli, made of a proteinaceous material, and arranged in one layer; shell surface smooth or irregular with numerous small pores; usually 3-4 nuclei, sometimes 5-6, with central nucleolus.

 

Dimensions: Cunningham 55 µm, Stepanek 63-67 µm, Todorov and Golemansky 60-70 µm; my measurements 44 µm (average).

 

Ecology: Fresh water, on waterplants; also reported from waste water (Todorov, 2003). Rare. I found this species once in considerable numbers in a sample from Crailoo, The Netherlands.

 

Literature:

Todorov, M. and Golemansky, V.: Morphology, Biometry and Ecology of Arcella excavata Cunningham, 1919 (Rhizopoda: Arcellinida) - Acta Protozool. (2003) 42: 105 - 111.

 

Arcella excavata
Arcella excavata
Arcella excavata
Arcella excavata
Arcella excavata
Arcella excavata
Arcella excavata
Arcella excavata