Test patelliform; rigid, transparent, punctate; aperture circular, almost the entire diameter of test; cytoplasm similar to that of Arcella; a single nucleus; one or more contractile vacuoles; fresh water. (ref. ID; 1618)
ref. ID; 1923
Aperture nearly as wide as the base of the shell. Shell with punctuate sometimes indistinct. (ref. ID; 1923)
Pyxidicula cymbalum Penard, 901 (ref. ID; 7850) or 1902 (ref. ID; 3693 original paper) reported year? (ref. ID; 1923, 7857)
Pyxidicula gibbosa Schonborn, 1966 (ref. ID; 1401, 2066 original paper)
Pyxidicula cymbalum Penard, 901 (ref. ID; 7850) or 1902 (ref. ID; 3693 original paper) reported year? (ref. ID; 1923, 7857)
Descriptions
Shell much larger, about 80 µm. Shell patelliform, brown in color, with distinct punctate. Aperture round, bordered very a narrow rim. Contractile vacuole single. Pseudopodia unknown. Habitat wet moss and Sphagnum. (ref. ID; 1923)
Arcella patens Carter, 1864 (ref. ID; 1332) or Carter, non Claparede & Lachmann (ref. ID; 3693); Arcella patens in Hertwig & Lesser, non Claparede & Lachmann (ref. ID; 3693)
Descriptions
Test smooth, colorless to brown; a single vesicular nucleus; pseudopodia short, lobose or digitate; on vegetation. (ref. ID; 1618)
With a narrow inverted margin, forming a large, circular orifice; membrane smooth, transparent, finely punctate, becoming darker or nearly brown with age. Habitat aquatic vegetation. (ref. ID; 1923)
The shell is discoid or hemispherical, composed of proteinaceous material, which varies in colour, being transparent or light yellow in young individuals and becoming darker with age to be either brown or red-brown. In contrast to Arcella, the aperture is almost as wide as the total diameter of the shell. It is uniform in outline and appears to have a slight thickening around the margin. In detail this thickening is a slightly depressed rim, which is recurved to give a small lip. The shell surface is smooth on the apertural margin, but the rest of the surface is covered by regularly spaced pits or pores. These pores are not visible on the inner surface, so presumably they fuse within the matrix. Portions of the broken rim show that it is a thin extension of the shell wall, which is constructed of a single layer of regular, interlocking alveoli. This alveoli are rectangular in vertical section with a depth of about 0.3 µm and have a solid content and thin walls. The contents of the alveoli did not permit embedding resin to penetrate the whole wall, and as a consequence sectioned material gave poor results. Nevertheless, sufficient information is available to reconstruct diagrammatically a cross-section through the wall. Each alveolus is surrounded by a single membrane-like structure, which is reffered to as the shell matrix, and at the outer surface the shell wall is bilaminar. (ref. ID; 4727)
Remarks
The testate amoeba Pyxidicula operculata was initially described by Agardh (1827) as a species of the diatom genus Frustulia and later transferred by him (1830) to another diatom genus, Cymbella. It was subsequently placed by Ehrenberg (1834) in his new genus Galionella as G.? (Pyxidicula) operculata, the genus Pyxidicula only later being given status in the name P. operculata by Ehrenberg (1838), although again it was still considered a diatom. The first report of this species as a rhizopod was that of Carter (1864), who noted that this specimens, identified as Arcella patens (Claparede and Lachmann, 1859) were "very like" Ehrenberg's P. operculata. It is assumed that because P. operculata was placed amongst the Diatomaceae by Ehrenberg, Carter rejected it as a name for his specimens, although he added that he thought there was much in common between the Rhizopoda and the Diatomaceae. It was not until Hertwig and Lesser (1874) that this species was first placed under its corrected name, P. operculata, in the Rhizopoda. Furthermore, the latter authors considered Carter's specimens identified as Arcella patens to be P. operculata, and not the Arcella patens described by Claparede and Lachmann (1859). (ref. ID; 4727)
Measurements
Diameter in 20 µm. (ref. ID; 1618)
Diameter 17-21 µm. (ref. ID; 1923)
Diameter 17.5-21.4 µm, depth 6.3-9.0 µm, diameter of aperture 13.6-17.1 µm, width of apertural lip 1.7-2.6 µm, with a lip depth no greater than 2.0 µm. (ref. ID; 4727)
Shell rounded with a moderate undular rim from ventral view, hat-like from side view. The shapeble shell constituted only of organic matter, shell surface coarse-grained (rim fine grained). On the vault part of the shell there are hemispherical little depressions in irregular radial rows. These depressions touch each other or are separate. Shell translucent, colorless or rusty brown. Aperture large, circular, with undular rim, can change its shape or size. (ref. ID; 4860)
Measurements
Diameter of the shell 184-209(196.5+/-12.5), height of the shell 89-108(98.5+/-9.5), aperture of the shell 126-161(143.5+/-17.5), width of the undular rim 17-26(21.5+/-4.5), diameter of the depression 7-11(9+/-2) µm (n=5). (ref. ID; 4860)
Aperture not invaginate or re-entrant. Shell minute, very depressed, almost saucer-shaped; membrane pale yellow-red, showing a faint punctation, sometimes coarsely scrobiculate. Habitat ponds and lakes. (ref. ID; 1923)
