Nuclearia Cienkowski, 1865 (ref. ID; 4224) reported year? (ref. ID; 1618, 2431) or Cienkowsky, 1865 (ref. ID; 3541, 4670) reported year? (ref. ID; 1923, 2240)

Phylum Sarcomastigophora Honigberg & Balamuth, 1963: Subphylum Sarcodina Hertwig & Lesser, 1874: Superclass Rhizopoda von Siebold, 1845: Class Filosea Leidy, 1879: Order Aconchulinida De Saedeleer, 1934: Family Nucleariidae nov. fam. (ref. ID; 4670 original paper)
Rhizopodea: Filosia: Order Aconchulinida (ref. ID; 7528)

[ref. ID; 1618]
Subspherical, with sharply pointed fine radiating pseudopodia; actively moving forms vary in shape; with or without a mucous envelop; with one or many nuclei; fresh water. (ref. ID; 1618)

[ref. ID; 1923]
Endoplasm colorless. Body amoeboid, normally spherical. (ref. ID; 1923)

[ref. ID; 4224]
Feeding by either ingestion of food particles or penetration of old/damaged eukaryotic algal filaments. Cells readily adopt a flattened form without severe compression being applied. Branching of pseudopodia occurs. Characteristic behavior of contractile vacuole. (ref. ID; 4224)

[ref. ID; 7586]
Contractile vacuole: This organism typically has one, but occasionaly more, contractile vacuoles. These may expel their contents at any point on the non-pseudopodial surface of the cell. During diastole, the contratile vacuole develops by the fusion of smaller vesicles and usually has an irregular outline. The onset of systole, shortly before the expulsion of the vacuolar contents, the vacuole takes on an apparently perfectly symmetrical appearance. During systole, some or all of the contents of the vacuole are expelled to the outside of the cell, but at the same time a halo of smaller vesicles appears around the periphery of the contractile vacuole. Although no accurate measurements have been made, it appears as if some of the fluid which fills these smaller vesicles is derived by backflow from the contractile vacuole. During the early stages of diastole, these peripheral vesicles, which persist after vacuolar systole, enlarge and fuse to form the new contractile vacuole. (ref. ID; 7586)

  1. Nuclearia caulescens Penard, 1903 (ref. ID; 3541, 3691)
  2. Nuclearia delicatula Cienkowski, 1865 (ref. ID; 4224, 4670) reported year? (ref. ID; 1618) or Cienkowsky (ref. ID; 2240)
    See; Heterophrys myriopoda (ref. ID; 2240)
  3. Nuclearia moebiusi Frenzel, 1897 (ref. ID; 4079) reported year? (ref. ID; 4224)
  4. Nuclearia radians Greeff
    See; Nucleosphaerium radians comb. nov. (ref. ID; 4224)
  5. Nuclearia simplex Cienkowski, 1865 (ref. ID; 2431, 4224, 4670) reported year? (ref. ID; 1618, 7528) or Cienkowsky (ref. ID; 1923)

Nuclearia delicatula Cienkowski, 1865 (ref. ID; 4224, 4670) reported year? (ref. ID; 1618) or Cienkowsky (ref. ID; 2240)


Heterophrys myriopoda (ref. ID; 2240)


Form changes, variable; 4-10 nuclei; bacteria often adhering to the gelatinous envelope. (ref. ID; 1618)

[ref. ID; 4224]


One of the most important features of N. delicatula is the easy transformation from the spherical to trophic form. Two place emphasis on the fact that "the shape of the body usually changes" (Artari 1889) and "the amoebae all appear to be endowed with an extreme plasticity" (Blanc-Brude et al. 1955). As this is the type species of the genus, and the trophic form is so prevalent and naturally occurring, adoption of a trophic forms should be a major consideration when packing naked filose amoebae in this group. A similar amoeba, but without motile form Nucleosphaerium tuckeri Cann & Page, is considered by Patterson (1984) to be same as Nuclearia radians Greeff. If this is so, Nucleosphaerium tuckeri should be reassigned as Nucleosphaerium radians comb. nov. No branching of pseudopodia is observed in Nucleosphaerium; there is no discernable trophic movement, except only occasionally under very severe compression from drying wet-mounts, and feeding is by ingestion only. Even centrohelid heliozoa will adopt a flattened form under such compression. Ultrastructural studies confirm previous observations of Nuclearia (Patterson 1983) that the pattern of nuclear division is mesomitotic (Page 1976), the nuclear membrane remaining intact. Mitochondia contain flattened cristae with do not branch or anastomose, unlike most other amoebae. They may be tubular or appear discoid as in Nuclearia moebiusi (Patterson 1983). The unique pattern of contractile vacuole behavior as described by Patterson (1981) is confirmed in the present study and is a potentially useful diagnostic character. (ref. ID; 4224)
N. delicatula Cienkowski, 1865, is very similar to Nucleosphaerium in that Cienkowski recorded the body as being usually spherical, and having a mucilaginous envelope. However the spherical shape is not a constant feature and the cell readily adopts a typical amoeboid form (Cienkowski 1865; Calkins 1901). When the cells of N. delicatula have a spherical form, the pseudopodia are typically filose and correspond the definition given above. However the motile forms have pointed pseudopodia produced from a flattened base. The pseudopodia in the genus Nuclearia are also observed to branch sometimes (Cienkowski 1865; Penard 1903; Sandon 1927; West 1903; Nikolyuk 1972), unlike the filopodia in Nucleosphaerium. N. delicatula is also an algal feeder (Calkins 1901), engulfing food particles of various kinds, usually smaller, however, than the Phormidum filaments that Nucleosphaerium engulfs. Because of this it is proposed to include Nuclearia in the new family Nucleariidae, which will be for filose amoebae which feed only by ingestion. Early observers described Nulearia as having a single nucleus (West 1903) or scattered nuclear material (multiple nucleoli) (Cienkowski 1865). However, they may well have taken the nucleolus for the entire nucleus. (ref. ID; 4670)


Up to 60 um in diameter. (ref. ID; 1618)

Nuclearia moebiusi Frenzel, 1897 (ref. ID; 4079) reported year? (ref. ID; 4224)


The cell may emit thin hyaline pseudopodia from any part of the body. When the cell is actively moving, it is flattened and the pseudopodia extend preferentially from the front and from the anterior lateral margins of the cell. When moving, the pseudopodia are resorbed by a process which involves crumpling at the posterior part of the cell. The pseudopodia may occasionally be seen to extend from a narrow hyaline margin around the edge of the cell body, although this is not often seen. The pseudopodia occasionally branch and do not anastomose. They bear no particle and have no evident axial structure. The pseudopodia taper a little along their length. When the cells are feeding, there is no evident anterio-posterior polarity, and pseudopodia extend from most parts of the cell. The cell is less flattened when it is feeding but was never observed to adopt a spherical form. There was no obvious mucus layer around the cell, nor were cysts observed at any time. Nuclearia feed by phagocytosis of small particles. Most active growth was supported by baker's yeast and by dried egg-yolk, both of which were ingested directly. Bacteria were also observed in food vacuoles. Nuclearia also consumed the cytoplasm of damaged Spirogyra cells but could not penetrate healthy cells off this alga. The alga Chlorococcum multinucleatum and Chlamydomas reinhardii were not taken as food, nor were the cyanobacteria Gloeotricha echinulata, Aphanizomemon flosaquae, Anabaena flos-aquae, Oscillatoria formosa, and Phromidium sp. Occasionally cells of Microcystis aeruginosa were ingested but this organism did not support active growth of the amoeba. Food vacuoles typically dominate the cytoplasm of organisms viewed with the light-microscope. There is a single contractile vacuole, the behavior of which is unlike that of many other amoebae in that vesicles appear around the periphery of the vacuole during fluid expulsion. The organism is typically, but not invariably, uninucleate. The nucleus contains a large round nucleolus often with a central, less dense spot. During nuclear division the nucleolus disappears and the pattern of division is mesomitotic, consistent with observations previously made on other members of this genus. Electron-micrographs show that the nucleus and food vacuoles dominate the cell. Sections passing vertically through the cell reveal that it is flattened. The nucleus is usually located near the center of the cell. It has a rounded granular nucleolus, occasionally with an electron-lucent central zone. The outer membrane of the nuclear envelope is often studded with ribosomes. The Golgi apparatus is comprised of a system of dictyosomes located in the perinuclear region. Despite its unusual behavior, the contractile vacuole complex has no peculiar ultrastructural characteristic. The spongiome is vesicular with some of the vesicles bearing a dense cytoplasmic coat. Pits and vesicles with a similar dense coat were associated with plasma membrane, which bears a finely filamentous external coat. Mitochondria are present in varying numbers in different cells. The cristae take the form of flattened rounded plates, but it has not been possible to determine if they have pedicel-like bases. The pseudopodia appear homogeneous as cytoplasmic organelles, including ribosomes, are excluded from them. Some profiles show irregularly shaped pseudopodia. These are interpreted as pseudopodia being resorbed. Often they contain vesicles whose membrane closely resembles that of the plasma membrane. The homogeneous cytoplasm of a pseudopodium extends into the cell as a tract. The cytoplasm contains numerous lipid droplets, and on one occasion a crystalline inclusion was observed. No extrusomes were seen at any time nor were any structures resembling lysosomes. The pattern of nuclear division when viewed by electron-microscopy differs slightly from the pattern observed with a light-microscope. At metaphase the nucleolus appears dispersed in the nucleoplasm. Microtubules extend away from the aligned chromosomes towards the poles. The microtubules were only ever detected within the nucleus. At not time was a discrete microtubular organizing center detected. During the stages when the microtubules are present the nuclear envelope is intact. At an apparently later stage in the division process, when no microtubules are present, the nucleoplasm and fragments of the nuclear envelope are contained within a single membrane. Clearly, at some stage reorganization of the nuclear envelope takes place. (ref. ID; 4079)


Nuclearia moebiusi is a small amoeboid organism, the body of which measures 15.2(+/-0.3) x 11.7(+/-0.3) um (Discophrya stock and 15.1(+/-0.3)x12.6(+/-0.4) um (Swanpool stock). (ref. ID; 4079)

Nuclearia simplex Cienkowski, 1865 (ref. ID; 2431, 4224, 4670) reported year? (ref. ID; 1618, 7528) or Cienkowsky (ref. ID; 1923)


Uninucleate. (ref. ID; 1618)
The body is capable of changing shape. Pseudopodia arising from all parts of the body. Nucleus central; contractile vacuoles, more than one. Reported only by Conn from Connecticut, this form seems to be doubtful. (ref. ID; 1923)
The ultrastructural study. (ref. ID; 7528)


N. simplex has a spherical body with radiating filose pseudopodia and appears very similar to Nucleospharium. However it was said by Cienkowski (1865) to encyst followed by the liberation of young amoebae. The amoeboid form of N. simplex was described by Pernin (1976). However the observations made were mainly on the behaviour of the organism under a cover slip. As in the case of Nucleospharium, N. simplex under a cover slip rapidly adopts a typical amoeboid form. However Pernin states that all forms of cell morphology are possible in N. simplex, from round to elongated and fusiform, which is unlike Nucleospharium. (ref. ID; 4670)


30 um in diameter. (ref. ID; 1618)
Diameter 20-50 um. (ref. ID; 1923)