A New Species from Mountain Forest Soils in Japan: Porosia paracarinata sp. nov., and Taxonomic Concept of the Genus Porosia Jung, 1942

A new species, Porosia paracarinata, is described from mountain forest litter, Bijodaira, Japan. This is the second species in the genus Porosia; until now, the genus was monospecific with the type species Porosia bigibbosa. P. paracarinata sp. nov. is distinguished from P. bigibbosa by the presence of a wide lateral keel. Test ultrastructure of P. paracarinata sp. nov. was documented using light and scanning electron microscopy. Morphometric analyses showed that this species is only slightly variable. The main morphological variability is due to the size of the lateral keel, which can vary from very wide (13.13 μm) to very narrow (3.75 μm). Ecological notes and morphological comparisons between P. paracarinata and other closely related species are discussed. The taxonomic concept of previously monospecific genus Porosia is expended.