Planhoogenraadia bonneti  Todorov & Golemansky, 1999

Diagnosis: The shell is brown, a type of simple cryptostomy, with a flattened ventral side. In dorsal view it is ovoid or ovoid-elongate, and very regular. In lateral view the shell is feebly bulging, with a maximum height near the middle of the length. The invagination of the aperture is shallow (1/6 to 1/5 of the height). The inner lip of the aperture is depressed and the outer lip is incurvate, forming a well differentiated visor. In ventral view the aperture is invaginated, oval, sub-terminal and easily visible. The shell has a comparatively thick wall and it is mainly composed of small, flattish siliceous particles. The arrangement of these particles makes its surface smooth, with a well defined outline.

Dimensions: According to Todorov & Golemansky (1999): Shell length 157—168 µm; width 122—130 µm; height 107—112 µm; aperture 70—75 µm; depth of aperture’s invagination 10-13 µm.

Ecology: Humid epiphytic mosses on tree trunks, height 1—2 m.

Geographical distribution: Thailand, Khao Yai National Park.

Remarks: P. bonneti differs distinctly from the other species of the genera Planhoogenraadia and Hoogenraadia by its biometric characterization. Planhoogenraadia alta Bonnet, 1984, and Hoogenraadia humicola Bonnet, 1974, are the most closely related species to P. bonneti.
Planhoogenraadia bonneti differs from P. alta by its wider and lower shell. Bonnet (1984) gave the average proportions for P. alta, as follows: Length/Width 1,6 and Height/Width 1,05. These proportions for P. bonneti are L/W 1,3 and H/W 0,87, respectively.
P. bonneti differs from P. alta by a comparatively thick wall of the shell, a brown color, higher shell dimensions and an absence of the small teeth on the dorsal lip of the visor. The two species are distinguished from each other also by their ecology. Bonnet (1984) observed P. alta in forest soils and fertile soils which were rich in organic matter, whereas P. bonneti inhabited humid epiphytic mosses.
Planhoogenraadia bonneti differs from H. humicola by its flattened ventral side and by the larger shell dimensions. Furthermore, the ecology of these species is different, too. Bonnet (1974) indicated that H. humicola inhabited soils rich in organic matter in dense forests of river outfall from tropical regions, whereas P. bonneti was a moss-inhabiting species.
So far Planhoogenraadia bonneti is the only known moss-inhabiting species. From morphological point of view it is also interesting that this species has larger shell dimensions (Length: 157-168 µm) in comparison with the rest of soil-inhabiting species.