Kasia Marciz asks this question:
I'm writing to ask about Schoenbornia humicola, more specifically, about the shell of the species.
I was trying to find information about the type of shell Schoenbornia humicol builds.
I contacted Ferry and he assured me about what I found in literature (paper attached, the original description as Pseudonebela humicola):
Schönborn describes the shell has having "siliceous plates as idiosomes" ("… mit Siliziumplättchen als Idiosomen"). Further he observed new-formed idiosoms in the cell plasm just like Euglypha ("Im Plasma der inaktiven Stadien beobachtete ich mehrmals vorgebildete Idiosomen ähnlich wie bei Eulgypha.").
Ferry Siemensma confirmed this.
Edward Mitchell believes these are not idiosomes because the platelets are not of uniform shape or size, at least according to the illustration used by Meisterfeld (2002). Rather they look at best as recycled idiosomes but may even be flat mineral such as mica.
Andrey Tsyganov agrees. "I agree with Edward that truly idiosomic species should have limited number of plates types of regular shape because they synthesize them. In case with Shoenbornia it seems that the plates are irregular in shape and size that rather points to extracellular origin of the plates than to unusual intracellular synthesis. "
Reference:
Meisterfeld, R. (2002) Order Arcellinida Kent, 1880. The illustrated guide to the protozoa (eds J. J. Lee, G. F. Leedale & P. Bradbury), pp. 827-860. Society of protozoologists, Lawrence, Kansas, USA.)
Schönborn, W. (1964) Bodenbewohnende Testaceen aus Deutschland. I. Unterstuchungen im Naturschutzgebiet Sarrahn (Macklenburg). Limnologica, 2, 105-122.
Edward Mitchell - Pseudopod your life!