Euglypha compressa Carter, 1864
Diagnosis: Shell large, broadly oviform, truncate, compressed, in cross-section lenticular with acute margins; shell composed of oval body plates and up to 40 thickened or stout siliceous spines; aperture circular or elliptical and surrounded by between eleven and fifteen, evenly spaced, denticulate oval apertural plates. The dentate edge is distally thickened around the large median tooth, but this thickening tapers evenly outwards to the three smaller teeth positioned on each side and equates with the normal shell thickness close to the last tooth. The apertural plates look in lateral view bluntly-denticulated or lobed, but are in oral view ornamented with some fine teeth; body plates arranged in sequence. They are roughly oval and often characterized by their hexagonal appearance, this latter feature is variable but the squared nature of the narrow margins is usually distinctive.
Spines vary greatly in length, often flattened, lanceolate or spatulate; The spines are positioned along the lateral margins from about the mid-body position to the aboral extremity. They are sometimes in pairs and usually alternate when viewed laterally, one pointing upwards and the next downwards along the length of the body. Each spine has a narrow base from which is tapers to its sides point about a quarter of the total spine length, then it tapes gradually over the remaining three quarters to the terminal point. Spines project from close to the lateral margins at an angle of 90 degrees to the shell surface. Individual spines appear to be semi-circular at their bases but taper distally to a point. Although these spines may vary in length, they are always stout compared with the thin spines of E. strigosa. Nucleus ovular, large, with several nucleoli.
Dimensions: 70-132 µm.
Ecology: Sphagnum and waterplants. According to Wailes (1915) this species is always associated with Assulina muscorum.
Remarks: in older descriptions the aperture scales are described as blunt or lobed, but each scale bears some teeth which are bent. They can only be observed when the aperture is turned towards the observer.
The shape of the spines is remarkable. They have a stout form and may be flattened, lanceolate or spear shaped. These forms are not always pronounced and spines may strongly differ in length. Specimens may have long spines, short spines or a mixture of both. Specimens with shorter spines are sometimes hard to distinguish from Euglypha ciliata.
The only recorded variety of this species is E. compressa f. glabra Cash et al., 1915, a form without spines. However, variation in the shape and size of the siliceous spines was also reported by Cash et al. for E. compressa, and such differences were considered to be a normal feature. Clonal cultures showed that differences in spine positioning is specific, structural differences of spine construction may also be specific. The spines described by De Graaf (1956) and Brown (1910), are different from those described by Ogden & Hedley (1980). In the latter report the spines are stout at the base, concave, and taper evenly to a point. Both types of spine are here considered to represent E. compressa, which is distinguished by the compressed shell and lateral position of the spine, but further work on clonal cultures may establish spine shape as a specific character.