Mallomonas pumilio group (Chrysophyceae/Stramenopiles) - a revision based on the scale/scale-case morphology and analysis of scale shape
Abstract
The species of the Mallomonas pumilio group belong to the smallest taxa of the genus (whole cells reach a length of ca. 12-14 mu m). This study is based on 244 silica scales of taxa sampled world-wide.
Detailed scale and scale-case morphology was investigated by transmission and scanning microscopy and scales were sorted into groups representing species and/or varieties. To evaluate the slight differences in scale morphology we used the methods of landmark-based geometric morphometrics (GM).
Homologous points (landmarks) were delimited to represent maximally the scale shape within each unit. Multivariate statistical procedures were used to test differences in shape between a priori set units.
The new species M. jubata was described and characterized. The varieties Mallomonas pumilio var. silvicola and M. pumilio var. munda were erected to the species level M silvicola and M munda, respectively.
The nominal variety of M pumilio was specified and the emended definition provided. Mallomonas directa, until now not distinguished from M pumilio var. pumilio, was separated on the bases of larger scales, different scale morphology and scale shape.
The new varieties M pumilio var. dispersa and M solea-ferrea var. irregularis were introduced. However, molecular data are needed to evaluate whether these taxa should be treated as varieties or separate species.
So far, none of the members of Mallomonas pumilio group has been sequenced.