Actinosphaerium akamae (Shigenaka, Watanabe and Suzaki, 1980)

Diagnosis: Nuclei with nucleolar material as a central cluster of granules, and with a cyst wall not incorporating siliceous components.

Habitat: Fresh water.

Remarks: Much of the information provided about this species relates to the dimensions of the cell, and proportions of endoplasm and ectoplasm (morphometric characters). The proportions of endoplasm to ectoplasm (2-14:1) appear to have been calculated (rather than measured) using the minimum of one value against the maximum of the other. If the values are summed, they gives sizes for cells outside the range described in the paper. The cyst of A. akamae does not incorporate siliceous components, but is composed of several organic (i. e. mucous, granular, fibrillar and electron-dense ones) layers (Shigenaka et al. 1985). The appearance of nuclei is similar to that of A. eichhornii although they are reported as slightly smaller. In view of the discrepancies over reports of nuclear size in A. eichhornii and in view of the variability of this character, this aspect requires re-investigation. While there is little doubt that different stocks investigated by the Japanese workers exhibited consistent and identifiable differences from which species, there are no absolute characters by which A. akamae can be identified except the absence of siliceous elements from the cyst. Given the overall similarity of this taxon to A. eichhornii, the uncertainty over some of the distinguishing characters, we treat the taxon as nomen dubium until the unusual nature of the cyst is confirmed and/or other discriminatory characters emerge (all remarks from Mikrjukov and Patterson, 2001).