monothalamian

from The Century Dictionary.

• Single-chambered; unilocular; having but one compartment: especially applied to Foraminifera of this character, in distinction from polythalamian. See cut under Foraminifera.
• noun An organism whose test or shell is unilocular or Monothalamous: said of cephalopods, and especially of foraminifers.
• noun Also monothalaman.