A New Species of Centrohelid Heliozoan Acanthocystis amura n. sp. Isolated From Two Remote Locations in Russia.

A new species of centrohelid heliozoan Acanthocystis amura from the Amur River, the Far East of Russia was studied with light- and electron microscopy. Acanthocystis amura has simple oval plate scales (1.2-2.6 × 1.0-1.8 μm) with an axial thickening and a thin border as well as two types of spine scales. The spine scales of type 1 were 1.3-4.8 μm long and had four small hooks on their tips. The spine scales of type 2 were shorter, 1.0-3.6 μm long and had four teeth at the distal end. The morphology of A. amura resembles that of Acanthocystis quadrifurca. They both have similar spine scales but their plate scales are completely different. Acanthocystis valdiviense differs from the new species in absence of hook-bearing scales. Molecular phylogeny based on 18S rDNA consistently placed A. amura into Acanthocystis nichollsi/Acanthocystis costata clade, but relationships between those three species were not resolved. Morphology of another centrohelid strain from another location (the South Urals) has been compared with that of the original strain and few minor differences in size characteristics of the scales have been revealed.