Platyamoeba Page, 1969

[ref. ID; 2359]
The glycocalyces of the Platyamoeba strains were generally thinner than those of the Thecamoeba species and were consistent in structure, with a compact inner layer and a less dense outer layer. The mean thicknesses of the entire glycocalyx ranged from 13 to 29 nm. The thickness of the compact layer was about 5 nm in all strains, but the less dense layer was more variable, even within a strain. This less dense layer appeared in some cases to be affected differently by different fixation methods. (ref. ID; 2359)
[Locomotive form] a flattened form, usually oval or somewhat fan-shaped in outline, with approximately the anterior half comprising the hyaline region and behind this a granular region which might be more or less rounded and thickened as a whole or thinner anteriorly toward the hyaline region. The hyaloplasm extended to varying degrees laterally around the granular region was a rounded mass; it might be only slightly convex (this term used to indicate a lesser degree of curvature) at other times and in some species was often more or less straight, even slightly concave at times. The 'semi-circular' shape was a flattened ovoid with the posterior edge more or less straightened. Another modification of shape was a slight antero-lateral squaring off of the arc-like edge of the hyaline region. The surface wrinkles characteristic of the genus as fleeting rather than persist in features were found to various degrees in the four species. (ref. ID; 2359)

[ref. ID; 2712]
On the whole the original diagnosis of the genus (Page, 1969), based on two freshwater species. It should be noted, however, that the phrase 'length usually greater than breadth' in the generic diagnosis might be misleading, since even the mean length:breadth ratio of some marine strains is less than 1. This character was intended to help distinguish between Platyamoeba and Vannella Bovee, 1965, but it is not essential, though the length often is greater than the breadth, while in Vannella the breadth is usually greater. It might also be noted that the occurrence of transient folds or wrinkles parallel to and near the edges is more common in some species (e.g. P. mainensis and P. flabellata) than in others. The mitotic pattern is more variable than was known when the genus was established but is still sufficient, with other criteria, to separate Platyamoeba from Vannella. For the principal distinctions between Platyamoeba and Thecamoeba and between Platyamoeba and Vannella the reader is referred to Page, 1969. It should be added that even in species of Thecamoeba in which the dorsal folds are inconspicuous, the hyaline zone is always a crescent with long lateral horns. (T. orbis Schaeffer, 1926, a fairly common marine amoeba, which has conspicuous dorsal folds, is the one species of Thecamoeba which on the basis of hyaline/granular division alone might be taken for a Platyamoeba). In Platyamoeba the hyaline region may at times take a veil-like form around the granular mass (in flabellate forms), but it is generally the anterior half of a flattened ovoid, sometimes with lateroposteriad extensions. In Vannella the hyaloplasm practically always forms a veil and the flabellate form is usual. The earlier judgment (Page, 1969) about the invalidity of the genus Rugipes Schaeffer, 1926, still seems correct, for the reasons given at that time. The other named genus most resembling Platyamoeba is Unda Schaeffer, 1926, but Schaeffer's description of its locomotion seems to distinguish them. However, T. K. Sawyer (personal communication) will shortly present a paper in which he classifies in several genera (including Rugipes) amoebae which would fall within the concept of Platyamoeba adopted here. The locomotive forms of all strains were variation of the general pattern of the genus Platyamoeba: a flattened form, usually oval or somewhat fan-shaped in outline, with approximately the anterior half comprising the hyaline region and behind this a granular region which might be more or less rounded and thickened as a whole (especially in P. flabellata) or thinner anteriorly toward the hyaline region. The hyaloplasm extended to varying degrees laterally around the granular region. The posterior edge of the amoeba was rounded when the granular region was a rounded mass; it might be only slightly convex (this term used to indicate a lesser degree of curvature) at other times and in some species was often more or less straight, even slightly concave at times. The 'semi-circular' shape was a flattened ovoid with the posterior edge more or less straightened. Another modification of shape was a slight antero-lateral squaring-off of the arc-like edge of the hyaline region. The surface wrinkles characteristic of the genus as fleeting rather than persisting features were found to various degrees in the four species, particularly when amoebae were changing direction or otherwise putting an unequal stress on different parts of the surface. They appeared somewhat less common in P. plurinucleolus than in the other species. Transverse ripples were often seen in the hyaline region. Locomotive activity was that characteristic of the genus Platyamoeba and the family Thecamoebidae as a whole: a general advance of the entire amoeba without production of discrete pseudopodia, though one or another area of the hyaloplasm might expand as the amoeba pushed forward or changed direction. There were thus gradual changes in shape and in length:breadth ratios. Occasionally the tractor-like movement of the cell surface was demonstrated by the paths of adherent particles, though prolonged adhesion of particles was not common. To test the cell surface for a mucopolysaccharide layer, periodic acid-Schiff's and alcian blue procedures were carried out on one strain of each species. On all cases, the results were negative or very weakly positive. (ref. ID; 2712)
Type species; Platyamoeba placida (ref. ID; 2712)

Platyamoeba bursella Page, 1974 (ref. ID; 2359, 2712 original paper)
Description; Salt water. The glycocalyx of this strain differed only slightly in thickness from those of P. plurinucleolus, P. placida and P. flabellata. The compact layer was 5 nm thick; the entire glycocalyx, 17-23 nm thick, with a mean of 20 nm. (ref. ID; 2359)
Over-all locomotive form usually a flattened ovoid or semi-circle, with thickness of granular region commonly as spindle-shaped or slenderly ovoid mass along posterior edge, which is usually straight or somewhat convex; breadth often greater than length, but those two dimensions equal on average; surface wrinkles sometimes occurring parallel to and near edges. Nucleolus central, rounded. No contractile vacuole. No cyst observed. Mesomitosis, with distinct though sometimes short spindle fibres and nuclear membrane in metaphase. Observed habitat: salt and slightly brackish water. (ref. ID; 2712)
Measurements; 15-40 um, average 22 um; Length : Breadth 0.6-1.4 (average 0.9) (ref. ID; 2359)
Greatest dimension in locomotion 20-30 um, with mean 18-21 um for two observed strains. Nuclear diameter 3.7-7.4 um in vivo. (ref. ID; 2712)
Platyamoeba calycinucleolus Page, 1974 (ref. ID; 2712 original paper)
Description; Over-all locomotive form usually a flattened ovoid or semi-circle, with thickness of granular region as spindle-shaped or ovoid mass along posterior edge, which is commonly straight or somewhat convex; length on average less than breadth, although it may be greater; surface wrinkles sometimes occurring parallel to and near to edges, especially during change of direction. Nucleolus central, usually cup-shaped with depression on one side and some of presumptive chromatin in cluster near concavity of nucleus. No contractile vacuole. No cyst observed. Mesomitosis, with distinct spindle fibres at metaphase; nuclear membrane present at beginning of metaphase but disappearing completely by anaphase. Observed habitat: salt and slightly brackish water. (ref. ID; 2712)
Measurements; Greatest dimension in locomotion 15-42 um, with marked divergence in range between two observed strains. Nuclear diameter 3.7-7.0 um in vivo. (ref. ID; 2712)
Platyamoeba flabellata Page, 1974 (ref. ID; 2359, 2712 original paper, 3847)
Description; Salt water. This strains have two-layered glycocalyces of very similar thicknesses. The compact layer measured 5 nm and the total thickness 15-20 nm, with a mean of 17 nm. (ref. ID; 2359)
Salt water. Over-all locomotive form often a flattened ovoid but with strong tendency to become flabellate; entire granular region commonly in a thickened ovoid or rounded mass; posterior edge often rounded or convex; length greater or less than breadth, but those two dimensions often equal; surface wrinkles often occurring parallel to and near to edges. Nucleolus central, rounded or polymorphic. No contractile vacuole. No cyst observed. Mesomitosis, with indistinct spindle throughout most of metaphase; nuclear membrane somewhat thickened in appearance in prophase and early metaphase, touching periphery of equatorial plate in mid-metaphase, then briefly forming thin caps at ends of spindles in late metaphase. (ref. ID; 2712)
Marine amoebae. (ref. ID; 3847)
Measurements; 21-36 um, average 30 um; Length: Breadth 0.7-1.5 (average 1.0) (ref. ID; 2359)
Greatest dimension in locomotion approximately 20-42 um, with mean 26-30 um for strains observed. Nuclear diameter 3.7-7.0 um in vivo. (ref. ID; 2712)
Platyamoeba langae Sawyer (ref. ID; 3847)
Description; Marine amoebae. (ref. ID; 3847)
Platyamoeba mainensis Page, 1971 (ref. ID; 2197 original paper, 2712)
Description; The marine amoebae. Flattened amoebae, with length greater than breadth; extensive anterior hyaline zone often continuing broadly around sides of posterior, raised, granular region. Often fine longitudinal lines or wrinkles near sides. Floating form usually irregularly rounded up, sometimes radiate with several slender, blunt pseudopods. Single vesicular nucleus with central nucleolus. No contractile vacuole. No cyst formed. Reproduction by binary fission; mesomitosis with persistence of fragments of nuclear membrane as polar caps. (ref. ID; 2197)
[Cultivation strain] This species was divided into an anterior hyaline and a posterior granular region like Thecamoeba orbis, the hyaline region was flatter relative to the humped granular region and formed a broad veil extending back nearly half the length of the amoeba and sometimes continuing back around the sides of the granular mass. The thin hyaline zone might wrinkle or crumple along its edge as one amoeba encountered another. The most distinct indication, in living amoebae, that this was a Platyamoeba rather than a Vannella was the frequent formation of slight longitudinal wrinkles near the sides of the amoeba, which often also show gentle, transverse, wave-like swellings during locomotion. These amoebae differed from Vannella also in almost always having a broadly rounded posterior edge, never drawn out into a long, spatulate form. P. mainensis gave the impression of having a very delicate pellicle-like surface. Only minority of floating forms had blunt, radiated pseudopods; most were very irregularly rounded up, adding to the impression of a thin but fairly rigid pellicle-like surface region. The nucleus had a central nucleolus, with a fragmented layer of chromatin material (no more than slightly Feulgen-positive) between nuclear membrane and nucleolus. In full-length sea water, some cells had a large, nearly clear vesicle which usually appeared to contain a few indistinct solid particles. One or two of these vesicles were seen to empty, but many cells did not possess them, and they appeared to be old food vacuoles rather than contractile vacuoles. Food vacuoles in general were not very conspicuous. Feeding was by invagination at the anterior edge. This species had an unusual pattern in which the nucleolus disappeared in prophase and the nuclear membrane was disrupted in late metaphase; but a cap which appeared to be a remnant of the nuclear membrane was seen on the polar side of each chromosome set in later stages. The wide clear space of halo around the mitotic figures was not separated from the granular cytoplasm by a distinguishable membrane. (ref. ID; 2197)
Measurements; Length in locomotion approximately 19-35 um; mean approximately 26 um; Length:breadth 1.0-1.4 (average 1.1). Nuclear diameter approximately 3.5-5.5; Nucleolus 2.0-4.0 um. (ref. ID; 2197)
Platyamoeba murchelanoi Sawyer (ref. ID; 3847)
Description; Marine amoebae. (ref. ID; 3847)
Platyamoeba placida Page, 1968 (ref. ID; 2359, 2712)
Description; Fresh water. This strains have two-layered glycocalyces of very similar thicknesses. The compact layer measured 5 nm and the total thickness 15-20 nm, with a mean of 17 nm. (ref. ID; 2359)
Habitat; fresh water. (ref. ID; 2712)
Measurements; 16-35 um; Length: Breadth 0.6-1.9 (average 1.2). (ref. ID; 2359)
Platyamoeba plurinucleolus Page, 1974 (ref. ID; 2359, 2712 original paper, 3847)
Description; Salt water. This strains have two-layered glycocalyces of very similar thicknesses. The compact layer measured 5 nm and the total thickness 15-20 nm, with a mean of 17 nm. (ref. ID; 2359)
Over-all locomotive form usually a flattened ovoid, with posterior edge rounded, slightly convex, or straight; granular region often as small ovoid mass along posterior edge, or gradually becoming thinner toward anterior border; length from somewhat less to somewhat greater than breadth; surface wrinkles sometimes occurring parallel to or near to edges, especially during change of direction. Nucleolar material in two or three peripheral fragments. No contractile vacuole. No cyst observed. Mesomitosis with distinct spindle fibres and with nuclear membrane present in metaphase but disappearing later. Observed habitat: salt water. (ref. ID; 2712)
Marine amoebae. (ref. ID; 3847)
Measurements; 9-21 um, average 15 um; Length: Breadth 0.9-1.6 (average 1.2) (ref. ID; 2359)
Greatest dimension in locomotion approximately 9-23 um, with means of observed strains 15-16 um. Nuclear diameter 2.4-4.6 um in fixed preparations. (ref. ID; 2712)
Platyamoeba stenopodia Page, 1969 (ref. ID; 2359, 2712)
Description; Fresh water. (ref. ID; 2359, 2712)
Measurements; 15-36 um, average 23.5 um; Length: Breadth 1.5-4.0 (average 2.0) (ref. ID; 2359)
Platyamoeba vivax (Schaeffer, 1926) (ref. ID; 2712)
Description; Marine amoebae. (ref. ID; 2712)