Planocarina carinata (Archer 1867) Kosakyan et al., 2016
Diagnosis: Test oval-pyriform in broad lateral view, laterally compressed with a well-defined lateral flat keel, usually broader than 4 µm. The keel begins near the pseudostome. Small lateral pores are usually visible on each side about one-third the distance between the pseudostome and the fundus of the test. Test almost transparent, composed of oval and circular test plates often intermixed with pieces of organic cement. Pseudostome slightly curved in broad lateral view, with a thick organic lip.
Dimensions: shell L: 140-246 µm, B: 110- 175 µm. Pseudostome: 27-43 µm.
Ecology: Sphagnum vegetation
Remarks: This species has a characteristic thin but broad keel, but as Cash et al., (1909) noted, the degree of development of this feature is not constant and they suggested that this probably indicated a wide range of variability. Therefore P. carinata specimens are sometimes hard to distinguish from those of P. marginata. I find both species often together.