Thecamoeba

Thecamoeba Fromentel, 1874 (ref. ID; 7510) or Fromental, 1874 emend. Singh & Hanumaiah, 1979 emend. Auctt. (ref. ID; 7594)

Superclass Rhizopoda: Class Lobosea: Subclass Gymnamoebia (ref. ID; 7510)
Order Amoebida Kent, 1880: Schizopyrenidae Singh, 1952 emend. Singh & Das, 1980 (ref. ID; 7594)
Amoebida: Thecamoebidae (ref. ID; 7532)

[ref. ID; 1923]
Without shell and flagellum, but with a pellicle. This genus has not a rayed stage. (ref. ID; 1923)

[ref. ID; 2197]
Amoebae of the genus Thecamoeba are often called "amoebae with a pellicle" (Penard 1905) because of the apparent stiffness of their surface layer with its folds and wrinkles. Although they have a traditional reputation as soil and moss inhabitants, they are common in both fresh and salt water. The "original" member and type-species of this genus is usually considered to be Amoeba verrucosa Ehrenberg, 1838, although probably neither Ehrenberg's amoeba nor that described by Dujardin (1841) under the same name is now identifiable. Most workers have followed the description of A. verrucosa given by Leidy (1879), as they have his description of A. proteus. Leidy, however, did include among his beautiful illustrations those of "younger stages" now recognized as separate species. It was de Fromental (1874) who established the genus Thecamoeba for amoebae with a "dermal thickening which covers the dorsal part"; and this genus, whether or not the name is appropriate, is certainly one of the most easily recognizable genera of amoebae, though Penard (1902) did not employ the generic name and Faure-Fremiet & Andre (1968) suggested that the genus was not distinct from Amoeba on the basis of an electron-microscopical study of the cortical region of T. terricola. Several species similar T. verrucosa, and now also included in the genus Thecamoeba, were described by Greeff (1866, 1891). T. striata was described in 1890 by Penard, who made further investigations of "amibes a pellicle" (Penard 1902, 1905, 1913). A total of at least 18 described species, including possible synonyms, may belong to the genus Thecamoeba. In 1926, Schaeffer established the family Thecamoebidae. In addition to describing six new species in that family, he recognized A. verrucosa, A. sphaeronucleolus, and A. striata as members of the genus Thecamoeba and erected the genus Rugipes. The latter is rejected by Bovee (1971) and Page (1969), since the type-species R. bilzi Schaeffer, 1926 is, in fact, a species of Thecamoeba. Page (1969) erected the genus Platyamoeba in this family. (ref. ID; 2197)

[ref. ID; 2359]
A flattened ovoid or oblong, rarely with length more than four times breadth, with longitudinal surface folds and light microscopy appearance of a thickened pellicle; hyaloplasm usually a crescent at anterior end, usually with slender lateral extensions toward posterior end; no discrete pseudopodia or branching in most species; normally uninucleate, with variety of nuclear structures among species; a thick glycocalyx, usually 20 nm or more. All species had a plasma membrane of the usual trilaminar, unit-membrane structure. (ref. ID; 2359)

[ref. ID; 2713]
Amoebae of this genus are larger than many other commonly found amoebae, with lengths often exceeding 50 um and sometimes up to 200 or 300 um. Their surfaces usually show wrinkles or ridges suggesting a pellicle-like nature, and the tractor-like movement of that surface is easily observed by means of adherent particles. Their flattened form makes observations of inclusions relatively easy. Ecologically also they are of special interest. Species of Thecamoeba are widely distributed in fresh water, occur in salt water, and are among the largest protozoa in soil. Earlier authors have especially associated them with soil and mosses, where they are indeed frequent, yet they apparently do not form cysts despite their occurrence in habitats subject to drying. Since they feed on a variety of protozoa and algae, as well as bacteria, they occupy a complex ecological position amongst the microbiota of both aquatic and terrestrial habitats. Furthermore, they are probably the easiest amoebae to identify, not only to genus but also to species, recommending themselves to ecologists as well as cell biologists. While many amoebae can be identified only if a fair number of individual cells are observed, sometimes only if cysts are obtained, it is possible to identify accurately to species a single Thecamoeba. It is, therefore, particularly unfortunate that there has been considerable confusion of species, partly because of the unavoidable inadequacy of the earliest descriptions, but also because characters of named species have been poorly defined even by later workers. Nearly any amoeba with a wrinkled appearance has been called 'Amoeba verrucosa'. Sometimes smaller ones with a relatively smooth contour and a few parallel folds on the dorsal (free) surface have been considered to be juvenile forms of Amoeba verrucosa or Amoeba terricola (Greeff 1866; Leidy 1879). Or all such smooth forms have been identified as Amoeba striata or striata-like amoebae. As in several other genera of amoeba, it is even impossible to identify with certainly the type-species, which legally is the nominal species Thecamoeba quadripartita Fromental, 1874. These difficulties are inherent not in the amoebae themselves, but in the descriptions. (ref. ID; 2713)

[ref. ID; 7510]
Page (1977) reported light-microscopical investigations of nine species and recognised nine others as probably or possibly valid. The most noticeable characters of the genus include a more or less flattened locomotive form, usually oblong, oval, or elliptical in outline and, in most species, never branching; prominent surface wrinkling or regular folds; and a crescent-shaped hyaloplasmic region. Locomotion is accompanied by an easily demonstrable tractor-like movement of the surface. Nuclear structure varies greatly, but in several species the nucleus somewhat resembles those of Amoeba and Chaos in containing numerous nucleoli. (ref. ID; 7510)

[ref. ID; 7594]
Definition; The resting nucleus contain two central more or less spherical closely apposed nucleoli. During mitosis 'polar masses' are formd and the nuclear membrane remains intact during division. Amoebae during locomotion are flattened having dermal thickening, the posterior end may be markedly tapering or triangular. (ref. ID; 7594)
Notes; Ehrenberg's Amoeba verrucosa is unidentifiable. Glaser (1912) first clearly described an amoeba under this name. This usage has been followed by Grell (1967, 1968). Both Glaser (1912) and Grell (1968) have reported the formation of 'polar masses' during mitosis in T. verrucosa and the nuclear membrane remains intact during divison. The mode of nuclear division in T. granifera has not been so far studied. Since its nuclear structure is exactly similar to T. verrucosa (see Page 1977), it is more logical to put this species in the genus Thecamoeba, based on its locomotive form and other morphological characters. It is not as highly wrinkled as T. verrucosa. T. granifera was isolated in clonal culture by Singh and Hanumaiah (1979) from Pune Mulla river mud, but unfortunately it was lost before its nuclear division could be studied. The structure of the resting nucleus and the locomotive morphology of the amoeba was exactly similar to that described by Page (1977). (ref. ID; 7594)
Type species; Thecamoeba verrucosa (Ehrenberg, 1838) sensu Glaser, 1912 (ref. ID; 7594)

Thecamoeba alba (Greeff, 1891) (ref. ID; 3687) reported author and year? (ref. ID; 2120)
Thecamoeba assimilis Lepsi, 1960 (ref. ID; 2713, 3687 original paper)
Thecamoeba bilizi (Schaeffer, 1926) (ref. ID; 2713)
Thecamoeba corrugata Bovee, 1953 (ref. ID; 2713)
Thecamoeba fibrillosa Greeff, 1891 (ref. ID; 3687)
Thecamoeba granifera (Greeff, 1866) (ref. ID; 2359, 2713, 7532)
Thecamoeba granifera Greeff minor Pussard, Alabouvette & Pons, 1979 (ref. ID; 7532 original paper)
Thecamoeba hilla Schaeffer, 1926 (ref. ID; 2197, 2713, 3687, 7594)
See; Carteria hilla (ref. ID; 7594)
Thecamoeba hoffmani Sawyer et al., 1974 (ref. ID; 2713)
Thecamoeba munda Schaeffer, 1926 (ref. ID; 2713, 3687)
Thecamoeba orbis Schaeffer, 1926 (ref. ID; 1335, 2197, 2359, 2713, 3687, 7594)
See; Carteria orbis (ref. ID; 7594)
Thecamoeba ovalis Lepsi, 1960 (ref. ID; 2713, 3687 original paper)
Thecamoeba papyracea (Penard, 1905) (ref. ID; 3687)
Thecamoeba proteoides (Page, 1976) (ref. ID; 1308, 2359, 2713 original paper, 7510)
Thecamoeba pulchra (Biernacka, 1963) (ref. ID; 2713)
Thecamoeba quadrilineata (Carter, 1856) (ref. ID; 2359, 2713, 3687) reported author and year? (ref. ID; 7586)
Thecamoeba quadripartita Fromental, 1874 (ref. ID; 2713)
See; Amoeba terricola (Ehrenberg) Penard, 1902 (ref. ID; 3693)
Thecamoeba rugosa Schaeffer, 1926 (ref. ID; 2713, 3687)
Thecamoeba simlis (Greeff, 1891) (ref. ID; 2359, 2431, 2713, 3687)
Thecamoeba sphaeronucleolus (Bovee) (ref. ID; 1308, 2120) or (Greeff, 1891) Bovee, 1960 (ref. ID; 2099, 2197)
Thecamoeba sphaeronucleolus (Greeff, 1891) (ref. ID; 2359, 2713, 3687)
Thecamoeba striata (Penard, 1890) (ref. ID; 2713, 3687) reported year? (ref. ID; 3496, 5624)
Thecamoeba striata (Penard, 1890) Schaeffer, 1926 (ref. ID; 1923, 2197, 2359, 2445)
Syn; Amoeba striata (ref. ID; 1923); Amoeba verrucosa Leidy, 1879 (ref. ID; 1923)
Thecamoeba terricola Greeff, 1866 (ref. ID; 2099, 2120, 2359, 2713, 3687)
Thecamoeba terricola (Page) (ref. ID; 1308)
Thecamoeba verrucosa (Ehrenberg, 1838) (ref. ID; 1923, 2713, 3687) reported year? (ref. ID; 3496)
Syn; Amoeba verrucosa Ehrenberg, 1838 (ref. ID; 1923); Thecamoeba quadripartita Fromentel, 1874 (ref. ID; 1923); Thecamoeba terricola Greeff, 1866 (ref. ID; 1923)
Thecamoeba verrucosa Glaser, 1912 (ref. ID; 1308, 1335)
See; Thecamoeba verrucosa Ehrenberg
Thecamoeba vesiculata (Penard, 1902) (ref. ID; 1307, 2713, 3687)

Thecamoeba assimilis Lepsi, 1960 (ref. ID; 2713, 3687 original paper)

Descriptions

Nominal species of questionable validity. Lepsi's book, which contained more new species names than any other publication on amoebae, was an attempt to combine all the older literature into one system and eliminate what Lepsi considered nomenclatural inconsistencies. This name is one which Lepsi applied to the figure of a nucleus which Penard (1905) labelled 'A. similis (?).' (ref. ID; 2713)

Thecamoeba bilizi (Schaeffer, 1926) (ref. ID; 2713)

Descriptions

Probably or possibly valid species. This is a fresh-water amoeba which Schaeffer (1926) made the type-species of a new genus Rugipes, which he distinguished from Thecamoeba on the basis that 'a true rayed stage' is formed by Rugipes but not Thecamoeba when disturbed, i.e. as a floating form. Rejection of the genus Rugipes was justified by Page, 1969. The species which Schaeffer called R. bilzi is, according to his description, a typical smooth Thecamoeba resembling T. striata in both locomotive form and nuclear structure, but somewhat larger. He gives its length in locomotion as 70-90 um, with on the average four to six parallel dorsal folds. In the nucleus, which has a long diameter about 9 um, there are three, sometimes four or more large, peripherally arranged endosomal pieces. Usually there is one highly deformable contractile vacuole, but there may be more, and the floating form had fairly long hyaline pseudopodia. These amoebae appeared in hay-infusion cultures inoculated with material from marshes in Tennessee, U.S.A. (ref. ID; 2713)

Thecamoeba corrugata Bovee, 1953 (ref. ID; 2713)

Descriptions

Probably or possibly valid species. Bovee (1953) distinguished this from T. striata as being smaller (30-40 um) and having usually about six dorsal folds, more than in the larger species. However, Bovee did no distinguish between T. striata and T. quadrilineata, and T. corrugata apparently had a nucleus resembling that of T. quadrilineata. Apparently no illustrations of T. corrugata have been published. (ref. ID; 2713)

Thecamoeba granifera (Greeff, 1866) (ref. ID; 2359, 2713, 7532)

Descriptions

The surface coating of this species differed strikingly from that of all others in thickness, structure, and chemical composition and will here be called a tegument rather than a glycocalyx. It was made up of three structurally distinguishable layers and was separated from the plasma membrane by a space of varying thickness. (ref. ID; 2359)

[ref. ID; 2713]
Stationary amoebae usually more or less discoid, with scallop-like wrinkles around edge; in locomotion a flattened, elongated ovoid or oblong with hyaloplasm as deep anterior crescent and extending far posteriorly as narrow border; anterior end often rather narrowed, with broadest point often at or just behind middle; often a broad, morulate uroid; pellicular folds lacking, or one on either side of granuloplasm, extending forward half length of amoeba or less; length approximately 48-85 um (mean 63 um), with length: breadth ratio approximately 1.3-2.4 (mean 1.8); endoplasm often full of golden-coloured lipoid globules; nucleus (7.7-12.4 um) with two more or less spherical closely apposed endsomal bodies, often of unequal sizes, one somewhat pocked, the other smooth and homogeneous; a single contractile vacuole, highly deformable, with diameter to about 12 um.

Locomotive morphology and inclusions: T. granifera had an even smoother appearance than T. quadrilineata and T. striata and never had several parallel dorsal striae. The folds mentioned in the description were only the edges of the raised posterior granuloplasm, and they never extended over this anterior hyaline cap as in the other two species. When the amoebae was advancing rapidly, the anterior hyaline end sometimes narrowed into a tongue-shaped area distinguishable from the oval main mass. The posterior end did not narrow as much as in the rugose species, and the knobby morulate uroid sometimes seen was approximately as wide as the anterior end. These amoebae sometimes changed direction by putting out a new hyaline bulge from the side, even near the posterior end. T. granifera is able, like other species of Thecamoeba, to reverse its direction of movement. An especially interesting aspect of T. granifera for the study of fine granules between the anterior hyaline cap and following mass of granuloplasm. Without careful observation, this zone of fine granules appeared to be part of the hyaloplasm, but it was distinguished especially well with differential interference contrast. There thus appeared to be two filtering mechanisms in this amoeba, one barring the fine granules from the hyaloplasm proper, and the other screening the coaser inclusions from this intermediate region. The present observations do not permit speculation on whether these filtering mechanisms are structural, as suggested for Amoeba proteus by Mast (1926) or at least partly theological. The locomotive rates of ten amoebae on the under side of a coverslip in a hanging-drop preparation were 88-104 um per minute. These amoebae adhered to glass better than most other species of Thecamoeba. In fixed preparations, the surface layer often appeared to be lefted off, i.e., separated from the main mass, either by shrinkage of the cytoplasm or by intrusion of fluid between the pellicle and the cytoplasm proper. The floating form was fairly well rounded up, often discoid with only surface scallopping, more regular than those of T. quadrilineata and T. striata, with a hyaline periphery. It quickly took on the extended locomotive form and began locomotion in a fresh wet mount. Somewhat similar forms were found in old cultures, where they may have represented somewhat dehydrated cells but were not otherwise differentiated as cysts. Probably the most immediately noticed feature of T. granifera was the occurrence in the endoplasm of a large number of gold-coloured refractile spherules, which often measured approximately 2 um but had a diameter at other times 0.5 um or less, occasionally somewhat larger than 2 um. These bodies, which appeared fairly solid when viewed under low power, were somewhat more translucent at higher magnifications. Since they concentrated Sudan black II to a marked degree, they were at least partly lipoidal, but they did not disappear with the addition of 95% ethanol to a wet mount. They did not give a positive reaction with the PAS procedure for polysaccharides, which produced a strong but differs rather than localized reaction in the granuloplasm. These highly coloured bodies were sometimes completely absent from cells, sometimes from most of those taken from a given culture, and their occurrence is probably associated with nutritional state. The contractile vacuole was highly deformable, comparable with those of T. quadrilineata and T. striata, though incised, lobed vacuoles were rare or absent in this species. (ref. ID; 2713)
Nuclear structure: The nucleus of T. granifera had a structure very similar to T. verrucosa. Upon first observation it appeared to contain a single central nucleolus. However, closer observation of living material, greatly assisted by phase contrast or differential interference contrast but possible with ordinary bright-field optics and careful focusing, revealed two approximately spherical intranuclear bodies. Grell (1968) called these nucleolus and Binnenkorper (endosome), but they will be given the non-committal name of endosome here, at least until completion of the mitotic study. One endosome had a somewhat granular texture and, with differential interference contrast, a pocked or pitted appearance. The other appeared more homogeneous and smooth. Optically the pocked or rough endosome appeared denser than the smooth one, and it was probably the former which was observed when only one was detected. This rough endosome had on the side toward the smooth one a slight depression in which the spherical smooth one seemed to be lodged, and the rough one was also often somewhat compressed rather than spherical. Of 100 nuclei, the two bodies appeared approximately equal in diameter in 37; the smooth one appeared larger in 50; and the rough one appeared larger in 13. The greatest diameter measured for either of the bodies was 7.7 um in a nucleus with diameter 10.8 um. In stained preparations, it was seldom possible to demonstrate a second endosome distinctly, whether with haematoxylin, Feulgen-fast green, or Kernechtrot. Just inside the nuclear membrane in such preparations was a layer of chromatin which was often weakly Feulgen-positive. Phase-contrast observations suggested that this layer was around the denser 'rough' endosome. The endosome have not been tested of presence of RNA; the smooth one did not take the fast green stain well as did the other. (ref. ID; 2713)

Identification and differentiation

This amoebae does not appear to have been identified correctly by any author after Greeff, although it must have been seen. The description by Greeff can easily be applied to the present strain. The lobose projections which his sketch shows must be at the posterior end, from the position of the vacuoles, and undoubtedly correspond to the broad uroid of this species. The similarity of the nucleus to that of T. verrucosa has been mentioned, but this could scarcely lead to a misidentification. Since the latter species is strongly rugose. (ref. ID; 2713)

Measurements

48-85 um, average 63 um. Measurements were made at some of the thinnest points along the tegument, preferably those where the trilaminar nature of the plasma membrane was distinguishable, since some of the thicker regions represented more or less tangential sections at that point. These measurements gave a total thickness, not including the plasma membrane or the space between plasma membrane and tegument proper, of 528-678 nm, commonly nearer the higher figure. The innermost layer of the tegument proper measured 298-424 nm and made up 55-63% of the total thickness. It consisted of spindle-shaped bodies, distinctly fibrous, lying parallel to the cell surface. The middle layer was 132-176 nm thick and occupied 21-32% of the total thickness. It consisted of roughly columnar structures, less distinctly formed than the spindle-shaped bodies of the inner layer, but also fibrous, at right angles to the cell surface. The outermost layer was 66-123 nm thick, or 12-18% of the total thickness, and was more amorphous and of a more even density than the other two layers, on the whole rather reticulate. The space between the plasma membrane and the tegument, largely electron-transparent, varied in thickness between approximately 40 and 90 nm because the plasma membrane and subject cytoplasm were thrown into hillocks, perhaps by fixation. It was traversed by sparse radial fibrils, each less than 2 nm thick, which continued into the innermost layer of the tegument proper. Radial fibrils could be perceived in the innermost and middle layers of the tegument and, with less certainty, in the outermost layers, but no single radial fibril could be traced through the entire tegumentary thickness. Both outer and inner surfaces of the tegument itself were much less uneven than was the cytoplasmic surface. (ref. ID; 2359)

Thecamoeba hilla Schaeffer, 1926 (ref. ID; 2197, 2713, 3687, 7594)

See

Carteria hilla (ref. ID; 7594)

Descriptions

The marine amoebae.

Cultivation strain: This species was in the same size range as T. striata and, had a smoother outline in locomotion than T. sphaeronucleolus. Their locomotive rate was much more rapid than that of T. sphaeronucleolus, and altogether they presented a less rigidly gelated appearance. They were more likely to have their greatest breadth near the anterior end than was T. striata; in locomotion the humped posterior end tended to be considerably narrower than the rest of the amoeba. Amoebae this species were least wrinkled in most active locomotion, when they usually had three to five (sometimes six) irregular space longitudinal folds on the free surface. Although an amoeba might form many fine surface wrinkles when stationary, these were much less conspicuous than those of T. sphaeronucleolus. The hyaline zone in active locomotion was a narrow crescent, usually about 1/10 the length of the entire cell in its anterior region and extending far back along the sides; in slow or stationary amoebae it was more extensive anteriorly. Frequently these amoebae reversed their direction of locomotion, resorbing the anterior hyaline zone and putting out a new one at the former posterior end. The nucleus of this species was bounded by a prominent membrane. It contained a central nucleolus, always in one piece, highly deformable, usually rather irregular, and sometimes quite elongate, so that its length might be twice its breadth. They thick layer of chromatin material between the nuclear membrane and the Feulgen-negative nucleolus was definitely and usually rather strongly Feulgen-positive. The large and highly deformable contractile vacuole present even in full-strength sea water often preceded the nucleus temporarily. Only once was an entire period timed, for an interval of 65 min, 5 sec, from one emptying of the vacuole to the next. Observations of vacuoles which were already large when first seen confirmed the great length of the contractile vacuole's period. Food vacuoles usually contained only bacteria, occasionally F. calkinsi, but never any of the abundant diatoms. The amoebae ingested clumps of bacteria near the anterior end. Some floating forms had ten or more broad, blunt pseudopods; most cells had fewer. (ref. ID; 2197)

[ref. ID; 2713]
Stationary amoebae usually smooth, sometimes with fine surface wrinkles; in locomotion flattened, ovate or obovate in outline, with greatest breadth usually somewhat anterior to middle of amoeba, posterior end sometimes tapering and with narrowed peak of granuloplasm but no knobby or shrivelled uroid; several parallel dorsal folds extending far anteriorly common in locomotive form; hyaloplasm an antero-lateral crescent fairly deep anteriorly and sometimes extending nearly to posterior end along sides of narrowed posterior peak of granuloplasm; length approximately 32-68 um (mean 50 um), with length: breadth ratio approximately 1.1-2.2 (mean 1.5); nucleus (7.5-12.5 um) with a single prominent central nucleolus of generally homogeneous structure; both nucleus and nucleolus highly deformable with length often twice breadth; a highly deformable vacuole.

Locomotive morphology and nuclear structure: This is a smooth species of Thecamoeba, although the form which was anteriorly broad and had a posterior tapering of the granuloplasm resembled a shape also seen in T. similis. These also often had a shape more similar to that ordinarily seen in T. quadrilineata and T. striata. The nucleolus was homogeneous in appearance, with a very few pit-like marks, and both nucleus and nucleolus changed shape rapidly as they were moved around by the cytoplasmic flow, so that they might be nearly round, approximately triangular, or, often, sausage-shaped. Observations made on the Mersea amoeba resembling this species showed an amoeba shaped much like T. quadrilineata or T. striata, and in approximately the same size range as the American strain of T. hilla. A vacuole was also present, though it was not seen to empty, as that of the American strain did very rarely. (ref. ID; 2713)

Measurements

Length 32-68 (average 50); nucleus 7.5-12.5; nucleolus 3.8-8.8; contractile vacuole diameter 7.5-10.0 um. Length:Breadth 1.1-2.2 (average 1.5). (ref. ID; 2197)

Thecamoeba hoffmani Sawyer et al., 1974 (ref. ID; 2713)

Descriptions

Probably or possibly valid species. This amoeba was described from sections of the gills of a fingerling rainbow trout, Salmo gairdneri, from a hatchery in the U.S.A., and Thecamoeba-like amoeba were also reported from salmonid fish in other American hatcheries. Amoebae were found, often in large numbers, between the gill lamellae, and it was concluded that they were involved in a pathological condition and mortalities in the hatchery. The length of the amoebae in the sectioned tissue were 21.6-40.8 um (mean 31.0 um), and the breadths 16.8-28.8 um (mean 23.1 um). The interphase nucleus had a thick, distinct nuclear membrane with either a single spherical nucleolus or with the nucleolar material fragmented. The authors believed that the amoeba were 'probably free-living in freshwater or present on or in gill tissue of fingerling salmonid fish as opportunists'. (ref. ID; 2713)

Thecamoeba munda Schaeffer, 1926 (ref. ID; 2713, 3687)

Descriptions

Probably or possibly valid species. This well-described marine species should be recognized if found again, care being taken to distinguish it from any Platyamoeba with a similar nuclear structure. It is of the smooth Thecamoeba type, with an oval outline and average length 45 um and breadth of 35 um in locomotion, with three or four prominent, parallel dorsal ridges. The nucleus, about 10 um in diameter, has two peripheral endosomal pieces. A large vacuole is usually present. Schaeffer found it in Florida, U.S.A., basing his description on four individual amoebae. (ref. ID; 2713)

Thecamoeba orbis Schaeffer, 1926 (ref. ID; 1335, 2197, 2359, 2713, 3687, 7594)

See

Carteria orbis (ref. ID; 7594)

Descriptions

Cultivation strain: This species usually had length and breadth very nearly the same, with a fairly circular outline, usually less arched posteriorly than anteriorly. The cell was divided into nearly equal anterior hyaline and posterior granular regions. The free surface bore one to four longitudinal folds or ridges, more prominent during more rapid locomotion. The nucleus, in the granular region had a single central nucleolus and an inconspicuous nuclear membrane not visible in living cells and not prominent even with Kernechtrot. The peripheral chromatin layer was distinctly Feulgen-positive. Nucleus and nucleolus were sometimes flattened antero-posteriorly. There was no contractile vacuole, and food vacuoles were usually inconspicuous. Bacteria were ingested by a broad invagination of the hyaline zone. The floating form had several rather short blunt pseudopods. (ref. ID; 2197)
This marine amoeba, small for a Thecamoeba, has a glycocalyx closely apposed to the plasma membrane consisting entirely of a compact layer approximately 16 to 22 nm thick. (ref. ID; 2359)
Stationary amoebae smooth; in locomotion flattened, with anterior outline more or less semi-circular and posterior edge somewhat convex, occasionally nearly straight, never narrowed posteriorly; surface sometimes temporarily smooth but usually with several parallel dorsal folds extending far anteriorly; hyaloplasm occupying approximately anterior half of cell with granuloplasm convex anteriorly; length approximately 11-22 um (mean 16 um); with length: breadth ratio approximately 0.7-1.4 (mean 1.1); nucleus (3.0-5.0 um) with a single central nucleolus and with nuclear membrane not distinct in vivo. The floating form sometimes had several blunt, hyaline pseudopodia. It should be noted that the nucleus was of the kind found in many amoebae, a simple vesiculate nucleus with the membrane ordinarily not visible in vivo. This appears to be a fairly widely distributed and not uncommon marine amoeba. (ref. ID; 2713)

Identification and differentiation

The very distinct dorsal folds usually though not always present distinguish it clearly from any species of Platyamoeba, with which it might otherwise be confused because of its size and the extent of the hyaloplasm. Platyamoeba plurinucleolus Page, 1974, is the described species with the most similar shape, but the nuclear structures are quite different. (ref. ID; 2713)

Measurements

Length 11-22 (average 16); nucleus 3.0-5.0; nucleolus 1.5-3.5 um. Length:Breadth 0.7-1.4 (average 1.1). (ref. ID; 2197)

Thecamoeba ovalis Lepsi, 1960 (ref. ID; 2713, 3687 original paper)

Descriptions

Nominal species of questionable validity. Lepsi gave the length as 35-40 um. His figure shows an amoeba resembling T. quadrilineata in nuclear structure but with a relatively greater anterior breadth than usually seen in T. quadrilineata, and Lepsi stated that it was broader anteriorly (than posteriorly). This may be a valid species. If so, it is a smooth Thecamoeba very similar to T. quadrilineata. Described from Rumania. (ref. ID; 2713)

Thecamoeba proteoides (Page, 1976) (ref. ID; 1308, 2359, 2713 original paper, 7510)

Descriptions

Freshwater. Under light microscopy this species much resembles Amoeba proteus but has characters which appear to place it in the present genus. Its surface structure was strikingly different from that of other species of Thecamoeba. Immediately external to the plasma membrane was an amorphous basal layers about 3-6 nm thick, but most of the total thickness of the cell coat was made up by a layer of distinct radial filaments, mostly extending 65-78 nm above the plasma membrane, some up to 117 nm. Each filament was about 2-3 nm thick. This cell surface strikingly recalls that of A. proteus, Chaos carolinense, and C. illinoisense, though the amorphous and filamentous coats are thinner in T. proteoides than in Amoeba and Chaos. T. proteoides was previously found to have a rather thin layer giving a positive reaction with alcian blue. Periodic acid/silver proteinate preparation made by the method Thiery showed localization of the silver in the amorphous basal layer, possibly because the material of that layer is denser than that of the filaments. (ref. ID; 2359)

[ref. ID; 2713]
In locomotion usually very elongated, a much flattened cylinder, monopodial or divided into two or more branches, with an anterior hyaline cap and a narrowed posterior end often bearing a morulate uroid; also somewhat shorter forms, broader anteriorly and often divided incompletely into two or three lobes; folds usually visible along part of length of advancing forms, particularly in posterior region; sometimes an extensive hyaline web between branches; cytoplasm highly alveolar; length of monopodial forms approximately 60-275 um (mean 174 um), of polypodial forms approximately 95-280 um (mean 171 um); length:breadth ratio of monopodial forms 1.4-10.5 (mean 4.0); nucleus more or less oblong, with numerous endosomal granules of fairly uniform size beneath nuclear membrane; nuclear diameter 12x8.5 um to 24x17 um; one to three contractile vacuoles. (ref. ID; 2713)

Locomotive morphology: Because of their length and frequent branching these bore a superficial resemblance to Amoeba proteus. However, differences were soon recognized. Actively advancing forms were monopodial more often that not, with a hemispherical anterior end with hyaline cap and a narrowed, usually shriveled-looking posterior end. Longitudinal surface folds were usually found along the posterior region, sometimes also farther forward, and there were sometimes occasional broad places along the length of the amoeba. Although a majority of the more actively advancing forms were monopodial, a fair number had one, occasionally two, side branches. There were sometimes flattened, hyaline webs between the bases of the branches, and surface folds were usually quite noticeable. Whether the amoebae were monopodial or polypodial, they were usually noticeably flattened, compared with A. proteus, despite their elongated, sub-cylindrical appearance. Even the slender pseudopodia of rapidly advancing amoebae might have a thickness not much more than one quarter of their breadth. Slowly moving amoebae sometimes had a broader, more obviously flattened form more easily recognizable as that of a Thecamoeba. T. proteoides moved well on a slide in fresh preparations, bacteria being sparse in these liquid cultures. The locomotive rates of ten amoebae ranged from 31 to 182 um per minute. The cytoplasm was highly alveolar, with the many vesicles rather spindle-shaped in advancing amoebae. The granuloplasm contained many yellowish refractile granules, mostly about 0.5 um, but no bodies with a recognizably crystalline shape. The contractile vacuole emptied with some outward bulging, usually on one side near the posterior end, often flattening on the proximal side as they emptied. The maximum contractile vacuole diameter measured was 14 um. When suspended in fluid, T. proteoides did not produce a flattening form with several long, slender pseudopodia radiating more or less symmetrically toward all sides as A. proteus often does. It might have various irregular shapes sometimes with two to three branches as in the polypodial locomotive form. (ref. ID; 2713)
Nuclear structure: The granular endosomal bodies were very small, 0.5 um or somewhat less. Although they were found in a peripheral layer, that layer was somewhat irregular with occasional gaps. In the interior of the nucleus one could sometimes distinguish threads, which if straightened out would be 7 um long or longer. The endosomal bodies were smaller than those of either T. terricola or T. similis. (ref. ID; 2713)

Identification and differentiation

Comparisons have already been made with A. proteus, and T. proteoides will not be miss-identified as A. proteus by anyone familiar with the latter organism and the generic characters of Thecamoeba. The one previously described species of Thecamoeba to which T. proteoides bears the more resemblance is T. vesiculata (Penard, 1902). T. vesiculata also has a rather elongated form, a highly alveolar cytoplasm, and a size in the same range as that of T. proteoides. However, Penard stated that his species never showed any 'bifurcation and development of arms'. Were it not for this statement, I should be inclined to identify the Bonn strains as belonging to Penard's species. It should be easily distinguished from T. terricola, since the nuclear structure is quite different and the latter species never becomes as T. proteoides, though it rarely shows a temporary division of the anterior end into two lobes when changing direction. (ref. ID; 2713)

Taxonomic position

The fine structure does not settle the question whether T. proteoides is placed more properly in the Thecamoebidae or the Amoebidae. Expressed briefly, the surface structure is more similar to that of the Amoebidae, the nuclear envelope more similar to that of Thecamoeba, and the other characters taxonomically unhelpful. However, upon closer examination, we find significant differences between the surface structure of T. proteoides and that of Amoeba/Chaos (e.g. depth of both amorphous and filamentous layers), while the multinucleate Chaos is more like Thecamoeba in its nuclear envelope structure than in Amoeba. There is as little uniformity within the family Amoebidae as within the genus Thecamoeba. This may suggest dismemberment of the genus Thecamoeba (Pussard 1973; Jahn, Bovee and Griffith 1974). We argue against this elsewhere (Page 1977), suggesting that it is necessary at this time to accept a degree of heterogeneity in this particular genus. The similarities between Thecamoeba and Amoeba, particularly between T. proteoides and Amoeba, may on the other hand be used to advocate incorporation of the former genus into the latter, as concluded by Faure-Fremiet and Andre (1968). But the differences are too great, and the argument for merging Amoeba and Chaos are just as strong, though there are ultrastructural reasons against doing so in addition to the multinuclearity of Chaos, which is the essential light-microscopical differences. The one positive statement which appears justified is that Thecamoeba and Amoeba are similar enough, compared with other amoebae, to guess at a relationship, perhaps a closer one than that suggested by the classification of Page (1976), certainly closer than that suggested by Jahn, Bovee and Griffith (1974). (ref. ID; 7510)

Comparison with other species

Faure-Fremiet and Andre (1968) found that T. terricola possesses a thick glycocalyx consisting of a dense inner layer (25-35 nm) and a less dense outer layer (possibly 50-70 nm). They reported microfibrillar elements in the outer layer but found no discrete filaments like those of T. proteoides. Likewise, Houssay and Prenant (1970) reported in T. sphaeronucleolus a dense, finely fibrillar layer (20 nm) bearing some filaments externally, but these filaments are, judging by their figure, sparse and irregular and do no form a continuous layer. We have found dense coatings on three other species of freshwater and soil Thecamoeba (unpublished). A fibrous lamina (internal dense lamella) seems also to be a common character of Thecamoeba, having been found by Faure-Fremiet and Andre (in Stevens and Andre 1969) in T. terricola and by Houssay and Prenant (1970) in T. sphaeronucleolus. Similar layer have also been found in four other freshwater and soil species of Thecamoeba (Page, unpublished). The only species of Thecamoeba for which descriptions of cytoplasmic organelles have been published previously is T. sphaeronucleolus (Houssay and Prenant 1970). The mitochondria of that species appear to be more of the elongated than those in our preparations of T. proteoides. As in T. proteoides, some of the cristae appear branched (plate 19, Houssay and Prenant 1970). Numerous dictyosomes were found, each consisting of approximately 12 cisternae. The endoplasmic reticulum of T. sphaeronucleolus is in the form of many small vesicles whose membranes are smooth or bear ribosomes. (ref. ID; 7510)

Measurements

60-280 um, average 171-174 um. (ref. ID; 2359)

Thecamoeba pulchra (Biernacka, 1963) (ref. ID; 2713)

Descriptions

Probably or possibly valid species. The similarity of this amoeba of T. hilla, but their identity is not established. It is a brackish-water organism, described from the Gulf of Danzig, and Biernacka stated that it has a large contractile vacuole. It is approximately 75 um long, of the smooth Thecamoeba type, and the nucleus has a central endosome. (ref. ID; 2713)

Thecamoeba quadrilineata (Carter, 1856) (ref. ID; 2359, 2713, 3687) reported author and year? (ref. ID; 7586)

Descriptions

Freshwater. Under light microscopy this species greatly resembles T. striata, except in nuclear structure. However, the cell surface has a somewhat different appearance. In all other species the glycocalyx lies closely apposed to the plasma membrane, but in T. quadrilineata three electron-dense layers, rather than the usual two dense layers of the plasma membrane, are seen beneath the compact glycocalyx. The same configuration was seen with both fixatives mentioned above. It therefore appears unlikely that the different appearance and the apparently greater thickness of the plasma membrane itself in this species are due merely to swelling during fixation. The appearance suggests that between the plasma membrane and the glycocalyx there is an electron-transparent layer approximately 6 nm thick and that the outermost of the three lines, approximately 5 nm thick where it can be distinguished at all, is the base of the glycocalyx. The glycocalyx proper (compact, dense layer) was about 24 nm thick. (ref. ID; 2359)

[ref. ID; 2713]
Stationary amoebae knobby but very little or not at all wrinkled; in locomotion flattened, oblong or elongately elliptical in outline, with broadest point usually just anterior to middle of amoeba and with posterior end usually broadly rounded; several parallel dorsal folds extending far anteriorly common in locomotive forms; hyaloplasm an antero-lateral crescent sometimes extending three-quarters of length posteriorly; length usually about 35-80 um (mean 50-55 um), but giant forms to 170 um long sometimes found; length: breadth ratio approximately 1.1-2.5 (mean 1.7-1.8); nucleus (7.7-11.0, to 15.0 um in giant forms) with a single central nucleolus (usually 4.6-7.4 um) of homogeneous texture; both nucleus and nucleolus highly deformable; a single contractile vacuole, highly deformable, with diameter to 15 um. (ref. ID; 2713)

Locomotive morphology: These smooth amoebae did not have the peripheral folds characteristic of rugose amoebae such as T. sphaeronucleolus, and their outline was on the whole smoother. Posteriorly they were seldom narrowed to a knob-like end. Generally in locomotion two to four dorsal striae were present. In a wet mount beneath a coverslip, they soon began locomotion, which, however, often ceased in a few minutes in preparations from an agar culture with numerous bacteria. Locomotion proceeded steadily and more rapidly, relative to the length of the amoebae, than in the rugose species, the measured rate ranging from 67 to 129 um per minute. The contractile vacuole, usually at or near the posterior end, was not only deformable (as are those of many amoebae) but subject to a temporary incision-like deformation of the membrane which might divide it into two or more lobes. It emptied with bulging, reaching a maximum diameter of about 15 um. The cytoplasm contained from a few to a fair number of refractile bodies, about 1.0-1.5 um, which were not discernibly crystalline. The floating form might be very irregularly rounded with hyaline bulges or might bear several pseudopodia with a length equal to or greater than the diameter of the central mass. (ref. ID; 2713)
Nuclear structure: This was the only non-marine Thecamoeba included in this investigation with a single, central nucleolus of visibly homogeneous structure, though almost certainly not the only existing species with such a nucleolus. Nucleus and nucleolus together were subject to marked deformation, so that they might be spherical, ovoid, or more or less reniform or triangular. The nucleolus was ever partly to wholly fragmented as in T. sphaeronucleolus. The diameters of measured nucleoli ranged from 4.6 um in a nucleus of 8.4 um to 7.5 um in a nucleus of 11 um. (ref. ID; 2713)

[ref. ID; 7586]

Contractile vacuole: The behavior of the contractile vacuole complex of this species closely resembles that of Amoeba proteus. There is typically a single contractile vacuole which circulates freely in the cytoplasm during diastole. It comes to lie in the uroidal region of the cell shortly before systole. At this time, the outline of the vacuole may be somewhat irregular. Shortly before the expulsion of its contents, the contractile vacuole becomes symmetrically rounded. During the expulsion of its contents, the contractile vacuole becomes flattened. No components of the contractile vacuole complex are visible once expulsion has been completed. The region of cytoplasm in which the emptying vacuole lay has a stiffened, gelated consistency. Diastole involves the enlargement and fusion of many small contributory vesicles which arise in or near this stiffened region of cytoplasm. Ultimately the contributory vesicles coalesce to form a single vacuole, arbitrarily called the contractile vacuole. Occasionally a few contributory vesicles may continue to circulate in the cytoplasm while the larger contractile vacuole enters systole. The contractile vacuole in this species may sometimes be sharply indented. This phenomenon is associated with one of the surface folds which characterise most species in this genus. (ref. ID; 7586)

Identification and differentiation

Undoubtedly T. quadrilineata has been regularly confused with T. striata ever since the description of the latter species. The only immediately noticeable difference is in nuclear structure. Penard (1890) in his original description of T. straita said: 'Noyau clair, oval-allonge, a nucleole divise en deux croissants etroits qui vont plaquer contre la membrane nucleaire tres fine.' However, in 1902 he suggested a variety of nuclear structures: 'En principe, il renferme un nucleole central, assez gros, en general perce de quelques vacuoles on lacunes; parfois on n'y trouve plus qu'une grosse vacuole centrale..., et la matiere chromatique est visible comme un anneau (en realite c'est une sphere creuse); puis cet anneau se voit dans d'autres exemplaires, remplace par des fragments plus ou moins ronds ou allonges, mais toujours arrondis a leurs extremites. Enfin on ne voit plus que qulques spherules pourvues souvent de vacuoles..., nageant dans le suc cellulaire, qui lui-meme est toujours finement granule. D'autres fois il reste un nucleole central assez grand encore, et d'autres spherules tres petites tout autour.' Cash (1905) did not describe the nucleus of the 'Amoeba striata' which he found other than as 'round', but his figures show nuclei resembling those of T. quadrilineata. Although Cash (1856) gave no adequate textual description of his Amoeba quadrilineata, his drawing shows very clearly the general form, division of hyaloplasm and granuloplasm, dorsal striae, contractile vacuole and nucleus what structure as described here. This must be recognized as a valid species, while maintaining also the separate existence of a species T. striata. The separation of the two distinct species is based on constancy of nuclear structure in four clonal strains of T. striata and two of T. quadrilineata, as well as other suggestive differences such as growth rate and adhesiveness to a glass substratum. It must be noted that Penard's varied description of T. striata were based on mixed material collected from the field at different times. Form the above it will be clear that T. quadrilineata can be distinguished from T. sphaeronucleolus by attention to the rugose versus smooth character and the structure of the nucleolus, which is coarsely granular and sometimes fragmented in T. sphaeronucleolus, and can easily be distinguished from T. striata by nuclear structure. Another similar amoeba, T. corrugata. (ref. ID; 2713)

Examined material

Thecamoeba quadrilineata was obtained from the Culture Centre for Algae and Protozoa, Cambridge, England, as stock number 1583/7. (ref. ID; 7586)

Measurements

35-80 um, average 50-55 um. (ref. ID; 2359)

Thecamoeba quadripartita Fromental, 1874 (ref. ID; 2713)

See

Amoeba terricola (Ehrenberg) Penard, 1902 (ref. ID; 3693)

Descriptions

Probably or possibly valid species. Despite the fact that 'The ... type-species of this genus is usually considered to be Amoeba verrucosa Ehrenberg, 1883' (Page, 1971), the type-species must be that to which Fromental (1874) gave the name Thecamoeba quadripartita, since in his generic diagnosis Fromental stated that he had established the genus for that amoeba. Fromental thought that the 'pellicle' of the Thecamoeba represented a kind of armour and that the parallel pellicular folds were lines dividing the oval cuirass into four parts. Both the description and the figure make it apparent that his Thecamoeba was of the smooth type. According to the scale, his amoeba was 100 um long, somewhat larger than any known Thecamoeba of the smooth type, but the apparent inaccuracy of some measurements of that period makes it possible that the amoeba actually might have been somewhat shorter. It was obviously a well-extended form. No nucleus is mentioned, and nothing in the figure can be safely interpreted as a nucleus. This seems to make it unlikely that it was T. quadrilineata, though that possibility remains, and it would be more likely to be T. striata, whose nucleus might not have been apparent as such. However, no positive identification can be made, and it is unlikely that the amoeba intended as the type-species will ever be unambiguously identified, unless a larger smooth Thecamoeba with an obscure nucleus is discovered. (ref. ID; 2713)

Thecamoeba rugosa Schaeffer, 1926 (ref. ID; 2713, 3687)

Descriptions

Probably or possibly valid species. This marine amoeba appears to be of the rugose type. Its length in locomotion is 60-80 um. The nucleus (10 um) has a homogeneous central nucleolus. One or more large vacuoles are usually present. Schaeffer described it as a 'voracious feeder' on blue-green algae and occasionally other algae. It was found in Florida, U.S.A. (ref. ID; 2713)

Thecamoeba simlis (Greeff, 1891) (ref. ID; 2359, 2431, 2713, 3687)

Descriptions

This species had a glycocalyx usually slightly more than 30 nm thick, consisting of a single compact layer closely apposed to the plasma membrane. With the Thiery silver proteinate procedure for glycoproteins, this layer was strongly positive and hence apparently identical with the alcian blue-positive acid mucopolysaccharide layer seen by light microscopy. (ref. ID; 2359)

[ref. ID; 2713]
Surface moderately wrinkled in stationary amoebae, becoming smoother in locomotion, usually with a few peripheral wrinkles, sometimes with a few dorsal folds converging somewhat posteriorly; outline in locomotion usually oval, broad or somewhat elongate, sometimes narrowing toward pyramidally hump-like posterior end; hyaloplasm a rather broad antero-lateral cresent; length approximately 30-80 um (mean 46-57 um), length: breadth ratio 0.8-1.8 (mean 1.2-1.4); nucleus (7.7-13.9 um) usually ovoidal or ellipsoidal with numerous small endosomal pieces in peripheral zone beneath nuclear membrane; a single contractile vacuole, with diameter to 13 um. (ref. ID; 2713)

Locomotive morphology: These amoebae approached the smooth type more than did any other rugose species investigated. They were less wrinkled than T. terricola and T. sphaeronucleolus. They quickly took the flattened form in some preparations, but in most preparations few showed locomotive activity, though such activity was occasionally seen in the vicinity of air bubbles. In fresh preparations containing few bacteria, locomotive activity was more common. These amoebae were typically broader than most other species of Thecamoeba, and sometimes the broad form was nearly fan-shaped. Neither a morulate nor a plicate uroid was seen, though the posterior end was often distinctly narrowed, contrasting with the usual forms of the smooth T. quadrilineata and T. striata. In actively advancing forms, three to five regular dorsal folds, more or less parallel or converging somewhat posteriorly were sometimes seen, and such amoebae approached T. quadrilineata and T. striata in appearance, though with a somewhat less regular outline and often a few peripheral wrinkles. T. similis was usually sluggish even when advancing steadily, rates of only 11-30 um per minute were measured, though in preparations from mixed cultures with few bacteria rates up to 72 um per minute were measured, still slower than the higher rates of the smooth species. Locomotion seldom continued for more than a minute, often less. The floating form was more or less irregularly rounded and knobby, never with distinct pseudopodia. (ref. ID; 2713)
Nuclear structure: The endosomal pieces were not only more numerous and smaller than in T. terricola but also, as Greeff described them, more clearly discrete pieces. The nucleus was never as elongated as it often was in T. terricola. (ref. ID; 2713)

Identification and differentiation

Greeff did not publish any illustrations of his Amoeba simils. The identification of these strains as his species is based on size relative to T. terricola, Greeff's comparison of the nuclei, and his comparison of the general appearance of the cytoplasm. (The assumption that Greeff's published measurements of T. terricola were incorrect is helpful again in this case, though it cannot be used in interpreting his descriptions of two other species, T. sphaeronucleolus and T. granifera). Penard's (1905) figure of a nucleus of 'A. similis (?)' is also taken into consideration. It is not really possible to be certain of the identity of Greeff's A. similis, but the present organism seems reasonably close to it. Care must be taken not to confuse T. similis with T. terricola, if one has not previously seen either. The most active locomotive forms with regular dorsal folds might also be taken for T. striata with a larger number of endosomal look more like a smooth than a rugose Thecamoeba. T. vesiculata has a nucleus with many endosomal pieces but is larger and much more elongated that T. similis. (ref. ID; 2713)

Measurements

30-80 um, average 46-57 um. (ref. ID; 2359)

Thecamoeba sphaeronucleolus (Bovee) (ref. ID; 1308, 2120) or (Greeff, 1891) Bovee, 1960 (ref. ID; 2099, 2197)

Descriptions

Cultivation strain: This species had a high wrinkled, stiff appearance in the usual stationary extended form on a slide; even ordinary cytoplasmic flow often could not be perceived. The average length of such stationary forms was 30 um. Locomotion was observed in amoebae in hanging drops, attached to the under side of cover glasses. These forms appeared much less wrinkled than the stationary ones. Fine wrinkles occurred along the sides, and there were four, five, or more fine folds on the dorsal (free) surface. Anteriorly the hyaline zone extended 1/12 to 1/7 the over-all length of the cell, continuing back along the sides more than 3/4 of the way to the posterior end. Its anterior extent was relatively greater in stationary extended forms. The nuclear membrane was very distinct even in living cells and appeared thicker than that of most amoebae. The nucleus itself was seldom if even spherical, usually ovoid, while the central nucleolus was more likely to be spherical. The nucleolus showed surface irregularities; occasionally it was fragmented into two or three pieces. The thick but diffuse chromatin layer between nucleolus and nuclear membrane was sometimes weakly Feulgen-positive. The nucleus and the food vacuoles were grouped toward the posterior end in locomotion. In moving amoebae the contractile vacuole, which seldom showed any identification, emptied at or near the posterior end. The floating form of T. sphaeronucleolus was irregularly rounded up with many short, blunt projections. (ref. ID; 2197)

Measurements

Length 80-130 (average 101); nucleus 11.0-15.5; nucleolus 5.0-8.0; contractile vacuole diameter 12.5-21.2 um. Length:Breadth 1.0-2.0 (average 1.5). (ref. ID; 2197)

Thecamoeba sphaeronucleolus (Greeff, 1891) (ref. ID; 2359, 2713, 3687)

Descriptions

Freshwater. The glycocalyx of this species had a maximum thickness of approximately 50 nm and, as in T. terricola, a compact inner and a less dense outer layer could be distinguished, though in this case the compact layer usually made up slightly less than one half of the total thickness. (ref. ID; 2359)
Surface strongly wrinkled in stationary amoebae, becoming somewhat smoother in locomotion, occasionally with several longitudinal dorsal folds in rapidly advancing amoebae; outline in locomotion often oblong or oval, sometimes broad with expanded anterior hyaline region, sometimes with knob-like uroid; hyaloplasm usually an antero-lateral crescent, in broader active forms sometimes spreading and flattening into a rather extensive sheet; length approximately 65-140 um (mean 98 um), length:breadth ratio 1.0-2.0 (mean 1.4); nucleus (11.0-15.5 um) usually with a single central nucleolus of coarsely granular, non-homogenerous texture, sometimes partly or completely fragmented into two or three lobes, which are never peripherally arranged; a single contractile vacuole, with diameter to 21 um. (ref. ID; 2713)

Identification and differentiation

Greeff did not publish any illustrations of this species, and his statement that this scarcely reaches half the size of his Amoeba similis leaves open to serious doubt that the species ordinarily identified as T. sphaeronucleolus is the one which Greeff had in mind. His description, including its attempt to 'unite' two previously named species under this name, is very unsatisfactory. Nevertheless, there seems to have been among workers who have used the name in this century good agreement on the amoeba intended, namely the one described by Penard (1902) under that name, and that is the species here considered to be T. sphaeronucleolus. Greeff (1891) spelled the specific epithet 'sphaeronucleosus', but most subsequent workers have followed Penard, using 'sphaeronucleolus'. Others (e.g., Horstmann 1968) have used the adjectival form "sphaeronucleolosus' which appears in meaning more correct than Greeff's name and in form more correct than Penard's, but the present usage is well-established. It should not be difficult to distinguish T. sphaeronuleolus from the two most similar rugose species, T. verrucosa and T. terricola, on the basis of nuclear structure alone, without considering size. It should likewise not be difficult to distinguish from T. quadrilineata, a distinctly smooth Thecamoeba with a nucleolus of homogeneous texture. Probably some of the 'verrucosa-like' amoebae in the literature belonged to this common species. (ref. ID; 2713)

Measurements

65-140 um, average 98 um. (ref. ID; 2359)

Thecamoeba striata (Penard, 1890) (ref. ID; 2713, 3687) reported year? (ref. ID; 3496, 5624)

Descriptions

Stationary amoebae knobby but very little or not at all wrinkled; in locomotion flattened, oblong or elongately elliptical in outline, with broadest point usually just anterior to middle of amoeba and with posterior end usually broadly rounded; several parallel dorsal folds extending far anteriorly common in locomotive form; hyaloplasm an antero-lateral crescent sometimes extending three-quarters of length posteriorly; length approximately 28-78 um (mean 48-52 um), with length:breadth ratio approximately 1.1-3.4 (mean 1.4-2.0); nucleus (6.5-10.0 um) with two, three, occasionally more nucleolar pieces arranged peripherally; a single contractile vacuole, highly deformable, with diameter to about 12.5 um. (ref. ID; 2713)

Identification and differentiation

This is most likely to be confused with T. quadrilineata. It might also be confused with T. similis, since cells of the latter species in a preparation with few bacteria may take an elongated, rather smooth locomotive form with a few dorsal striae. However, T. similis is likely in a short time to pass into a more characteristic form. I have discounted some of my own few noted observations of possible T. striata from terrestrial habitats on the ground that it would have been possible to take a T. similis for a T. striata with an exceptionally large number of nucleolar pieces. As a matter of fact, T. striata in clonal culture never had nuclei resembling those of T. similis. (ref. ID; 2713)

Thecamoeba striata (Penard, 1890) Schaeffer, 1926 (ref. ID; 1923, 2197, 2359, 2445)

Synonym

Amoeba striata (ref. ID; 1923); Amoeba verrucosa Leidy, 1879 (ref. ID; 1923)

Descriptions

Somewhat similar to A. verrucosa, but small; body flattened; ovoid narrowed and rounded posteriorly; nucleus vesicular; contractile vacuole comparatively large and often not spherical; extremely delicate pellicle shows three or four fine longitudinal lines which appear and disappear with the movement of the body; fresh water among vegetation. (ref. ID; 1923)

Cultivation strain: This species had a much smoother surface and more regular outline than the larger T. sphaeronucleolus. It moved more rapidly and occasionally became considerably more elongated than the latter. On a flat slide under a cover glass, the stationary extended forms had a rigid but not wrinkled appearance. The hyaline zone, which extended posteriorly along the sides, measured in its anterior region from 1/8 to 1/4 the total length of the cell. In locomotion the free (dorsal) surface bore three to five (usually three or four) prominent longitudinal ridges or folds. The amoebae were usually broadest near the middle of their length. The nucleus, bounded y a distinct but highly deformable membrane, was usually irregularly ovoid in outline. No living or fixed nucleus of these strains had a central nucleolus, and observations of these strains were in keeping with Penard's (1890) original description of the species as having the nucleolus divided into two narrow crescents against the inner surface f the nuclear membrane. The nucleolar or endosomal material usually appeared to be in two or three pieces apposed to the nuclear membrane, although as many as six apparent pieces. Some probably lobes of the same piece, were seen occasion. Rarely there appeared to be only one long, peripheral endosomal piece. The usually fragmented, peripheral arrangement of the Feulgen-negative nucleolar material is an important diagnostic characteristic of T. striata. The rest of the nuclear space was occupied by filamentous and granular material which was rarely Feulgen-positive. In fixed preparations, the nucleus was often surrounded by a halo-like clear space. Another characteristic structure of the species is the highly deformable contractile vacuole, often sharply indented. On one occasion such a vacuole was cut in two by cytoplasmic flow, the smaller vacuoles traveling independently for a few seconds and the rejoining. Large clumps of bacteria were ingested by a food cup at the anterior end and by means of broad lateral invaginations. Occasionally floating forms were more often irregularly rounded up. (ref. ID; 2197)

The glycocalyx of this species had the same appearance as that of T. similis but was slightly thinner approximately 26 nm thick. (ref. ID; 2359)

Measurements

25-45 by 20-35 um. (ref. ID; 1923)

Strain 75: Length 28-78 (average 48); nucleus 7.0-10.0; contractile vacuole diameter 10.0-12.2 um. Length:Breadth 1.1-2.2 (average 1.5). (ref. ID; 2197)
Strain 76: Length 30-62 (average 49); nucleus 6.0-9.0; contractile vacuole diameter 6.0-12.5 um. Length:Breadth 1.2-2.3 (average 1.7). (ref. ID; 2197)
Strain 77: Length 32-78 (average 52); nucleus 6.5-9.0; contractile vacuole diameter 8.8-11.2 um. Length:Breadth 1.4-3.4 (average 2.0). (ref. ID; 2197)

28-78, average 48-52 um. (ref. ID; 2359)

Thecamoeba terricola Greeff, 1866 (ref. ID; 2099, 2120, 2359, 2713, 3687)

Descriptions

Surface highly wrinkled in stationary amoebae, becoming somewhat smoother in locomotion but still usually wrinkled along edges and sometimes with fine surface wrinkles; outline in locomotion more or less oblong, sometimes triangular with broad end in advance; a more or less wrinkled posterior end, sometimes a plicate uroid; hyaloplasm ordinarily an antero-lateral crescent, sometimes with small hyaline knobs or scallops anteriorly; length ranging approximately from 60 to 170 um, with mean 110-120 um and length:breadth ratio 1.1 to 2.4 (mean 1.6-1.7); nucleus (15-31 um or larger) usually an elongate ellipsoid, with rather large endosomal pieces of various sizes arranged in layer beneath the nuclear membrane; a single contractile vacuole, with diameter to about 18 um. (ref. ID; 2713)

Locomotive morphology: This amoeba was not as rigid or as highly wrinkled as T. sphaeronucleolus under a coverslip and often did in fact go through normal locomotive activity for a short time. Greeff's drawings of its various forms are very accurate, including the occasional temporary short branching (more of a shallow cleaving) while changing direction, which is rare among species of Thecamoeba. I have never seen a villous uroid on this species, as depicted in some individual cells by Greeff, and such a cluster of fine projections seems very unlikely in a Thecamoeba, but it is difficult to know what other interpretation to put on Greeff's illustrations. On the other hand, the plicate uroid, also shown by Greeff, was occasionally seen in amoebae with a greatly narrowed posterior end. The locomotive rate of ten amoebae on an agar plate ranged from 48 to 144 um per minute. The floating form of this species when just suspended in fluid was irregularly rounded and bumpy, without pseudopodia. (ref. ID; 2713)
Nuclear structure: This corresponded well with that shown by Greeff. The endosomal pieces varied greatly in size, with larger ones around the narrow ends of the nuclei observed and smaller ones between them. Occasionally there appeared to be endosomal material in the centre of the nucleus, but these may have been pecies from either of the horizontal sides of the nucleus. When the amoebae were stationary, the nuclei were often somewhat more rounded than those figured. (ref. ID; 2713)

Identification and differentiation

One would have no problem at all in identifying our isolates with Greeff's amoebae were it not for the size difference. According to Greeff, fully grown amoebae reach 350-400 um. However, other authors have reported much lower figures. Penard (1902) said that they may reach 300 um but that large size was rare; in 1905 he gave the diameter when rounded up as 77-121 um, and a little less than double that figure for the elongated state. Grosse-Allermann (1909) gave a range of 90-200 um, rarely larger. Mattes (1924) found a mean of 110 um. Faure-Fremiet & Andre (1968) reported a diameter of 70-100 um when approximately spheroid. If we assume that Greeff made an error in his 1866 calculations, there is no difficulty at all in identifying our isolates as his species, since they are in the range given by other authors. Another possible explanation is gigantism, as described below for T. quadrilineata, but that was not observed in out cultures of T. terricola. Some authors (e.g., Cash 1905; Grosse-Allermann 1909; Bovee 1960) have considered T. terricola and T. verrucosa to be synonymous. This question will be examined in connection with the latter species. T. terricola is easily distinguishable from the rugose T. sphaeronucleolus on the basis of nuclear structure. It differs from T. similis not only in size and details of locomotive morphology but also in nuclear structure. The nucleus of T. similis is less elongated, and the endosomal pieces are more numerous, smaller, and to light microscope of more nearly the same size than those in T. terricola. It differs from T. proteoides in locomotive form, the latter species being longer and often truly branched, and in structure of the nucleus, which in the latter species has more and smaller endosomal bodies. (ref. ID; 2713)

Measurements

60-170 um, average 110-120 um. (ref. ID; 2359)

Thecamoeba verrucosa (Ehrenberg, 1838) (ref. ID; 1923, 2713, 3687) reported year? (ref. ID; 3496)

Synonym

Amoeba verrucosa Ehrenberg, 1838 (ref. ID; 1923); Thecamoeba quadripartita Fromentel, 1874 (ref. ID; 1923); Thecamoeba terricola Greeff, 1866 (ref. ID; 1923)

Descriptions

Ovoid in general outline with wart-like expansions body surface usually wrinkled, with a definite pellicle; pseudopodia short, broad and blunt, very slowly formed; nucleus ovoid, vesicular, with a large endosome; contractile vacuole; fresh water among algae. Pseudopods very short, broad lobes. Moves very slowly. Surface of the membrane marked by lines giving a wrinkled appearance. (ref. ID; 1923)
Probably or possibly valid species. Ehrenberg's Amoeba verrucosa is even more identifiable than T. quadripartita, since neither the description nor the figures permit any certainty even about the genus represented, though it could be a Thecamoeba. Even Leidy's (1879) A. verrucosa cannot be identified to species, taking the larger individuals rather than the ones which Leidy considered to be 'the young of A. verrucosa'. The alleged synonymy of T. terricola (the junior name) and A. verrucosa has been mentioned previously. Since the original Amoeba verrucosa can never be identified, a synonymy cannot be proved or disproved. The first clear description of an amoeba under this name with which I am acquainted is that of Glaser, 1912, and the name is therefore used here in the sense of Glaser. This usage has been followed by Grell (1967, 1968), who presented a cinematographic record of an amoeba which seems unquestionably to belong to the same species as that of Glaser. This is a rugose amoeba with a nuclear structure apparently corresponding exactly with that of T. granifera, which has a quite different locomotive morphology. Grell described an unusual mitotic process and the participation of the two intranuclear bodies in that process, an account agreeing in detail with that of Glaser. It is interesting that Granata (1914) described a very similar mitotic process for Haplosporidium limnodrili, parasitic in the gut epithelium of an oligochaete and a very different kind of organism from T. verrucosa. The interphase nuclear structure of the parasite was also very similar to those of T. verrucosa and T. granifera. Unfortunately, I have not yet been able to isolate T. verrucosa from fresh water, soil, or moss. Possibly it is less common that T. terricola, which seems to have been seen more often. (ref. ID; 2713)

Measurements

250-300 um. (ref. ID; 1923)
Up to 200 um in diameter. (ref. ID; 2713)

Thecamoeba vesiculata (Penard, 1902) (ref. ID; 1307, 2713, 3687)

Descriptions

Probably or possibly valid species. Statement of Penard was that 'there is never any bifurcation or development of arms'. Penard described it as taking a limax form in rapid advance, typically three or four times as long as broad, reaching easily a length of 200 um. The description of the 'pellicle' and the uroid also recall T. proteoides. The intranuclear material Penard showed as clumps of fine granules, and the endoplasm may be highly vacuolated. It has two or three contractile vacuoles. However, the lack of branching and the rounded, knobby stationary form make it almost certain that this is a species distinct from T. proteoides. Penard described it from Switzerland. (ref. ID; 2713)